characterization of biogenic volatile organic compounds and meteorology at azusa during the...

Atmospheric Environment 37 Supplement No. 2 (2003) S181–S196

Characterization of biogenic volatile organic compounds andmeteorology at Azusa during the SCOS97-NARSTO

Anni Reissella,1, Clinton MacDonaldb, Paul Robertsb, Janet Areya,*,2

aAir Pollution Research Center, University of California, Riverside, CA 92521, USAbSonoma Technology, Inc., 1360 Redwood Way, Suite C, Petaluma, CA 94954, USA

Received 4 March 2002; accepted 10 March 2003

Abstract

Meteorological modeling and analyses were performed for the 4–6 August and 4–6 September 1997 intensive

sampling episodes of the 1997 Southern California Ozone Study (SCOS97-NARSTO). This investigation was

conducted to study the connection of measured and modeled meteorological phenomenon with measured biogenic

volatile organic compound (BVOC) concentrations. Trajectory and surface wind analysis for five out of the six intensive

sampling days indicated that drainage flow from the mountains at nighttime and early morning affected the BVOCs

measured at the Azusa, CA monitoring site. Nitric oxide emissions from vehicles precluded nighttime chemical

reactions of the BVOCs at Azusa, allowing overnight accumulation of local monoterpene emissions in addition to

monoterpenes transported by drainage flows. The monoterpene mixing ratios maximized in the early morning hours

and the monoterpene/CO ratios showed sharp maxima at 0300–0600 h PDT on all days. In contrast, normalization of

benzene to CO diminished its diurnal variation, consistent with vehicle traffic as the source for these two long-lived

anthropogenic compounds. Substantial early morning methacrolein (MACR) and methyl vinyl ketone (MVK) mixing

ratios (and high (MACR + MVK)/isoprene ratios) measured at Azusa on all episode days were consistent with

drainage flow from elevated sites which had received NOx emissions and ozone transported from the urban basin by

daytime upslope flows. Isolation of these elevated sites from the basin NO emissions as the nocturnal boundary layer

was established would allow rapid nighttime nitrate radical reaction with isoprene, or slower isoprene reaction with

ozone, to produce high (MACR + MVK)/isoprene ratios in drainage flows into Azusa.

r 2003 Elsevier Ltd. All rights reserved.

Keywords: Biogenic volatile organic compounds; Meteorological modeling; Monoterpenes; Isoprene

1. Introduction

On a global scale, biogenic volatile organic com-

pounds (BVOCs), non-methane organic compounds

emitted from vegetation, are estimated to exceed

anthropogenic non-methane VOC emissions (M .uller,

1992; Piccot et al., 1992; Guenther et al., 1995, 2000;

World Meteorological Organization, 1995), and hence

have a considerable effect on tropospheric chemistry

(Trainer et al., 1987a; Fehsenfeld et al., 1992;

Fuentes et al., 2000). Measurements and modeling

studies have shown that BVOCs contribute to ozone

formation in rural and urban areas (Trainer et al.,

1987b; Chameides et al., 1988, 1992; Biesenthal

et al., 1997; Starn et al., 1998), and also play a

significant role in particle formation (Went, 1960;

Hoffmann et al., 1997; Kavouras et al., 1999; Griffin

et al., 1999).

ARTICLE IN PRESS

AE International – North America

*Corresponding author. Tel.: +1-909-787-3502; fax: +1-

909-787-5004.

E-mail addresses: [email protected] (A. Reissell),

[email protected] (C. MacDonald), paul@sonomatech.

com (P. Roberts), [email protected] (J. Arey).1Present address: Division of Atmospheric Sciences, Depart-

ment of Physical Sciences, P.O. Box 64, 00014 University of

Helsinki, Finland.2Also at Department of Environmental Sciences, University

of California, Riverside.

1352-2310/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S1352-2310(03)00390-X

The Southern California Ozone Study (SCOS97-

NARSTO) measurement program was carried out in

summer 1997 in order to investigate the formation and

transport of ozone, and to improve and expand

databases to support photochemical modeling in the

Los Angeles Basin and Southern California. The severe

photochemical air pollution experienced in the Los

Angeles Basin is attributed to emissions from contin-

uous urban traffic and a persistent eastern Pacific high-

pressure system especially during summertime, with

complex meteorological conditions influenced by sur-

rounding mountains on three sides and the Pacific

Ocean on the southwest. To examine the potential role

of biogenic volatile organic compounds in ozone

formation, BVOCs were measured at several sites in

the basin, including elevated locations, during SCOS97-

NARSTO intensive sampling episodes. Measurements

of isoprene, its atmospheric transformation products

methacrolein (MACR) and methyl vinyl ketone

(MVK), and monoterpenes at elevated locations near

Azusa have previously been reported (Reissell and Arey,

2001).

Based on archived SCOS97-NARSTO surface and

aloft wind, temperature, and mixing height data,

meteorological modeling and analysis were performed

to aid in interpreting BVOC measurements at Azusa and

contrasting these with aromatic VOCs and CO, routi-

nely monitored measures of traffic emissions. In

particular, back trajectories of air parcels arriving at

Azusa in early morning were calculated for two

SCOS97-NARSTO intensive sampling periods, 4–6

August and 4–6 September, in order to examine possible

source areas for the BVOCs measured at Azusa.

An attempt is made to reconcile the predicted BVOC

sources, the known chemistry of the BVOCs and the

measured meteorological parameters with the observed

ambient BVOC mixing ratios.

2. Experimental procedures

2.1. Site

Azusa is located midbasin in California’s densely

populated and heavily vehicle traffic-impacted South

Coast Air Basin and is about 4–5 km from the base of

the San Gabriel Mountains. The front range of the San

Gabriel Mountains, which trends roughly WNW-ESE,

lies to the north of Azusa and reaches heights of about

900–2100m above sea level (m asl). This front range

rises sharply from the basin, with steep slopes and

rugged canyons. The mouth of the San Gabriel Canyon,

a prominent NE-SW trending canyon that extends down

to the basin from the San Gabriel Reservoir, lies

approximately 3–4 km NNE of Azusa. The highest

mountains in the area, with elevations above 2100m asl,

are located approximately 13–16 km north and north-

west of Azusa.

The predominant natural plant communities of the

San Gabriel Mountains include Chamise series and

Chamise-hoaryleaf ceanothus series. Live oak chaparral

series and mixed chaparral shrublands also occur. At

higher elevations, Ponderosa pine series with some

Bigcone Douglas-fir series and Bigcone Douglas-fir-

canyon live oak series occurs on north-facing slopes.

(Information summarized from http://www.fs.fed.us/r5/

projects/ecoregions/m262bd.htm, an Ecological Subre-

gions of California website operated by the Pacific

Southwest region of the US Forest Service).

2.2. Meteorological analyses

2.2.1. Surface wind data, mixing heights and ventilation

For each episode day hourly surface wind data at

Azusa and Glendora (see Fig. 1) were reviewed and the

direction, scalar wind speed for each persistent flow

direction (typically onshore during the day and offshore

at night), and duration of flow types were noted.

Morning and afternoon mixing heights were deter-

mined from a variety of sources to produce the best

estimate of mixing heights at Azusa. At Azusa, sodar

(sound detection and ranging) wind data were available

to estimate morning mixing heights for the August

episode only. Therefore, for the August and September

episodes, the 0800 to 0900 h PDT mixing heights at El

Monte (see emt in Fig. 1) were estimated using RASS

(radio acoustic sounding system) virtual temperature

(Tv) data coupled with surface Tv data, radar profiler

reflectivity data, and lidar (light detection and ranging)

ozone data. The morning mixing heights at El Monte for

the August episode were compared to the depth of the

drainage flow as shown by the available sodar data

collected at Azusa. In this way it was verified that the

morning mixing heights at El Monte were similar to the

morning mixing heights at Azusa. Due to the limited

altitude range, it was not possible to determine after-

noon mixing heights from the sodar data. Therefore,

afternoon mixing heights were estimated at El Monte

using the radar profiler reflectivity data and the lidar

ozone data, and at Pomona using ozonesonde data.

Since El Monte is located about 15 km southwest of

Azusa and Pomona is located about 15 km to the

southeast of Azusa, the mixing heights from these

locations give a reasonable range of likely afternoon

mixing heights at Azusa.

As noted, the 0800 to 0900 h PDT morning mixing

heights at El Monte were taken as representative of the

mixing heights at Azusa. Furthermore, the mixing height

data indicated that the 0800–0900 h PDT mixing heights

were representative of the overnight boundary layer

depth and not the morning convective boundary layer

depth. Therefore, to estimate overnight and early

ARTICLE IN PRESSA. Reissell et al. / Atmospheric Environment 37 Supplement No. 2 (2003) S181–S196S182

http://www.fs.fed.us/r5/projects/ecoregions/m262bd.htm

http://www.fs.fed.us/r5/projects/ecoregions/m262bd.htm

morning ventilation, the daily 0800–0900 h PDT mixing

heights from El Monte were multiplied by the average

overnight scalar wind speeds at Azusa to give a

‘‘ventilation index’’.

2.2.2. Calmet wind model

Hourly three-dimensional wind fields and back-

trajectories were produced using the CALMET diag-

nostic wind model to characterize the flow patterns

during the episodes. The CALMET meteorological

model (Scire et al., 1999) is a software tool that

combines objective and diagnostic analysis methods to

create three-dimensional meteorological wind fields for

use in modeling and analysis.

The inputs to the CALMET meteorological model

consisted of surface terrain heights, surface wind data,

mixing heights, and upper-air wind data. US Geological

Survey fine resolution topography was spatially aver-

aged and gridded to prepare the terrain height inputs for

the SCOS97-NARSTO study region. The aloft wind

data were quality-controlled radar profiler wind data

collected at 26 sites (MacDonald et al., 2002). The

locations of the radar wind profilers (RWPs) in the

modeling domain and additional sites of interest are

shown in Fig. 1 and the site details are given in Table 1.

The surface wind data were obtained from the SCOS97-

NARSTO data archive and comprised data collected at

244 sites, including the Azusa study site and nearby

Glendora. The wind fields were developed with 4-km

horizontal resolution. The vertical structure of the wind

fields was tailored to the RWP range gates to ensure that

the 22 wind field layers corresponded as closely as

possible to the observed wind levels of the RWPs.

A number of sources of uncertainty are associated

with the CALMET wind fields and trajectories. As a

diagnostic wind model, CALMET is an interpolator

with parameterizations that account for the effects of

terrain and stability on the wind fields in areas of limited

observations. In this regard, as the density and

representativeness of input data improves, the results

from these types of models become more robust. Since

the SCOS97-NARSTO had a high density network of

both upper-air and surface sites, the CALMET wind

fields should give a reasonable estimate of the wind flow

in the modeling domain and the trajectories should give

a reasonable estimate of the air parcel paths.

For each episode day, plots of the CALMET wind

fields and 24-h 158m above ground level (m agl) back

trajectories arriving at Azusa at times that correspond to

the 0300–0600 h PDT and 0600–0900 h PDT VOC

sampling periods were prepared. Each trajectory plot

was reviewed and the general parcel paths were recorded

and the probable emission source areas were noted.

2.3. VOC sampling and analyses

2.3.1. Biogenic VOCs

Sampling was conducted on the roof of the South

Coast Air Quality Management District (SCAQMD)

monitoring station at Azusa. Samples were collected on

adsorbent tubes at the sampling site, transported to the

laboratory, spiked with gaseous internal standards,

subsequently thermally desorbed and analyzed by gas

ARTICLE IN PRESS

Fig. 1. Modeling domain in Southern California showing location of 26 radar wind profiler sites during the SCOS97-NARSTO field

study (see Table 1 for site identifications) and the locations of Azusa, Pine Mountain, Glendora and Pomona monitoring sites.

A. Reissell et al. / Atmospheric Environment 37 Supplement No. 2 (2003) S181–S196 S183

chromatography with a mass selective detector (MSD).

Ozone scrubbers (Cu–MnO2 plies in PFTE compression

fitting, Calogirou et al., 1996), were placed in front of

the sampling tubes and sampling was conducted at a

flow rate of 50ml min�1 using diaphragm pumps

(Thomas) and mass flow controllers (Tylan General).

A detailed description of the analysis procedures is

presented elsewhere (Reissell and Arey, 2001).

For the 4–6 August sampling period the sampling

intervals were 3 h during the daytime and 7 h during

nighttime. The sampling periods were 0300–0600,

0600–0900, 0900–1200, 1300–1600, 1700–2000, and

2000–0300 h local Pacific daylight time (PDT). During

the 4–6 September sampling period, more frequent

nighttime sampling was conducted and the nighttime

sampling periods were 1700–2000, 2000–2400, 2400–

0300 and 0300–0600 h PDT. Duplicate samples were

collected for BVOC quantification and based on all the

samples collected at Azusa during SCOS97-NARSTO

the precision for the BVOCs was: isoprene711%,

MACR 731%, MVK733%, a-pinene726%, limo-

nene722%, and 1,8-cineole718% (Reissell and Arey,

2001).

2.3.2. Anthropogenic VOCs

The anthropogenic VOCs discussed in this study are

the aromatic compounds benzene, toluene, ethylben-

zene, m-xylene, p-xylene, and o-xylene. The methods

used for sampling and analysis were those specified by

the US Environmental Protection Agency for the

enhanced O3 monitoring Photochemical Assessment

Monitoring Stations (PAMS).

At Azusa VOC samples were collected through a glass

inlet probe on the roof of the SCAQMD monitoring

station on a routine basis with an automatic multiple-

event canister collection system designed for around-the-

clock collection frequency. Eight three-hour integrated

samples were collected every day starting at midnight

(PDT) each day. After collection the canisters were

analyzed by gas chromatography with flame ionization

detection on an auto-GC at Pico Rivera operated by the

SCAQMD. A Nafion dryer was used to control

moisture in the samples. The SCOS97-NARSTO data

set was obtained from the California Air Resources

Board (CARB, 2000), supplemented by recent updates

to the m-xylene and p-xylene data (SCAQMD, 2001).

3. Results and discussion

3.1. VOCs and meteorology at Azusa

The VOCs measured at Azusa can be examined most

conveniently in three groups: (1) anthropogenic aro-

matic compounds emitted from vehicle traffic (benzene,

toluene, ethylbenzene, m-xylene, p-xylene, and o-xylene);

(2) monoterpene BVOCs (a-pinene, sabinene, b-pinene,limonene, and the oxygenated monoterpene derivative

1,8-cineole) which are emitted from vegetation as a

positive function of temperature; and (3) isoprene (a

BVOC whose emission requires light and increases with

temperature) and its major carbonyl reaction products

methacrolein (MACR) and methyl vinyl ketone (MVK).

Times series for the sum of the mixing ratios of the six

aromatic compounds, the sum of the mixing ratios of the

four monoterpenes, and the mixing ratios of isoprene,

MACR, and MVK from Azusa are shown in the top

panels of Figs. 2 and 3 for the 4–6 August and 4–6

ARTICLE IN PRESS

Table 1

Location and elevation of SCOS97-NARSTO radar wind

profiler (upper-air wind data) and RASS (virtual temperature)

sites and the Azusa, Pine Mountain, Glendora and Pomona

monitoring sites

Site name Site ID Latitude Longitude Elevation

(m asl)

El Montea emt 34.09 118.03 95

Norton ntn 34.09 117.26 318

Alpine ape 32.86 116.81 463

Brown Field bfd 32.57 116.99 158

Carlsbad cbd 33.14 117.27 110

El Centro eco 32.83 115.57 �18

Goleta gla 34.43 119.85 4

Los Alamitos las 33.79 118.05 7

Palmdale pde 34.61 118.09 777

Port Hueneme phe 34.17 119.22 2

San Clemente Island sce 33.02 118.59 53

Santa Catalina Island scl 33.45 118.48 37

Tustin ttn 33.71 117.84 16

Central Los Angeles usc 34.02 118.28 67

Van Nuys vns 34.22 118.49 241

Los Angeles Int. lax 33.94 118.44 47

Ontario ont 34.06 117.58 280

Point Loma plm 32.70 117.25 23

Valley Center vlc 33.26 117.04 415

Barstow btw 34.92 117.31 694

Hesperia hpa 34.39 117.40 975

Riverside rsd 33.92 117.31 488

Temecula tcl 33.50 117.16 335

Thermal tml 33.64 116.16 �36

Vandenberg AFB vaf 34.77 120.53 149

Simi Valley smi 34.29 118.80 279

Azusab,c 34.14 117.92 183

Pine Mountaind 34.22 117.90 B1350

Glendorab 34.15 117.84 237

Pomonae 34.06 117.76 259

aAlso lidar O3 data site.bSurface winds available.cSite of BVOC measurements (this work) and PAMS VOC

measurement site.dSite of BVOC measurements; 1383m on 4–6 August 1997

and 1311m on 4–7 September 1997 (Reissell and Arey, 2001).eOzonesonde data available (CARB, 2000).

A. Reissell et al. / Atmospheric Environment 37 Supplement No. 2 (2003) S181–S196S184

ARTIC

LEIN

PRES

S

Fig. 2. Diurnal profiles and ratios for VOCs and BVOCs at Azusa, 4–6 August 1997. Top panels, diurnal profiles of ambient concentrations (ppbv) of: the sum of aromatic VOCs

(includes benzene, toluene, ethylbenzene, m-xylene, p-xylene, and o-xylene); the sum of the monoterpenes (includes a-pinene, limonene, sabinene, and b-pinene); and isoprene,

methacrolein (MACR) and methyl vinyl ketone (MVK). Middle panels, ambient concentrations normalized to 0.001 x carbon monoxide: the sum of benzene/CO; the monoterpenes/

CO; and isoprene/CO. Bottom panels: selected ambient concentrations and ratios indicative of atmospheric chemistry: m-xylene/benzene ratio; reactive monoterpenes and cineole;

and ratio of the sum of isoprene atmospheric reaction products to isoprene. (Note all times are local, PDT and a vertical line marks 0600–0900 h each morning.)

A.

Reissell

eta

l./

Atm

osp

heric

En

viron

men

t3

7S

up

plem

ent

No

.2

(2

00

3)

S1

81

–S

19

6S185

ARTIC

LEIN

PRES

S

Fig. 3. Diurnal profiles and ratios for VOCs and BVOCs at Azusa, 4–6 September, 1997. Top panels, diurnal profiles of ambient concentrations (ppbv) of: the sum of aromatic

VOCs (includes benzene, toluene, ethylbenzene, m-xylene, p-xylene, and o-xylene); the sum of the monoterpenes (includes a-pinene, limonene, sabinene, and b-pinene); and isoprene,

methacrolein (MACR) and methyl vinyl ketone (MVK). Middle panels, ambient concentrations normalized to 0.001 x carbon monoxide: the sum of benzene/CO; the monoterpenes/

CO; and isoprene/CO. Bottom panels: selected ambient concentrations and ratios indicative of atmospheric chemistry: m-xylene/benzene ratio; reactive monoterpenes and cineole;

and ratio of the sum of isoprene atmospheric reaction products to isoprene. (Note all times are local, PDT and a vertical line marks 0600–0900 h each morning.)

A.

Reissell

eta

l./

Atm

osp

heric

En

viron

men

t3

7S

up

plem

ent

No

.2

(2

00

3)

S1

81

–S

19

6S186

September intensive sampling periods, respectively. The

diurnal profiles of these organic compounds are strongly

influenced by mixing heights, but important differences

among the compounds are obvious when their concen-

trations are normalized to CO, a non-reactive tracer for

vehicle traffic (middle panels in Figs. 2 and 3).

Alkene BVOCs react rapidly in the troposphere with

hydroxyl (OH) radicals, nitrate (NO3) radicals, and

ozone (O3) (Atkinson, 1997, 2000). Calculated lifetimes

(time for decay of the VOC to 1/e of its initial

concentration) of representative VOC and BVOC

compounds are given in Table 2. It should be noted

that the lifetimes given are inversely proportional to the

OH radical, NO3 radical and O3 concentrations

assumed. The complex interplay of the spatial and

temporal variations in OH radicals, NO3 radicals and O3

with the local meteorology and topography and the

resulting influence on the BVOC and VOC concentra-

tions at Azusa are discussed below in conjunction with

the bottom panels in Figs. 2 and 3.

3.1.1. Anthropogenic aromatic compounds

Azusa is considered as a midbasin receptor site for

anthropogenic VOCs, being located east of the main

source area of downtown Los Angeles. The monitoring

site in Azusa was close to the 10 and 210 freeways. As

seen from Table 3, during these intensive sampling

periods generally southwesterly winds prevailed at

Azusa during daytime and easterly winds during night-

time. The 0800–0900 h PDT mixing heights ranged from

250m agl on 4 August and 4 September to 600m agl on

6 September. In August, the sum of the aromatic

compound mixing ratios (see Fig. 2) clearly shows

morning maxima at 0600–0900 h PDT and minima in

the late afternoon (1500–1800 h PDT). The trend is

similar in September (see Fig. 3), but the maxima and

minima are less pronounced. The aromatic compounds

are emitted from traffic, which is continuous on the

nearby freeways and, therefore, these compounds

accumulate within the shallow mixed layer at nighttime

and peak during the early morning rush hour. The sharp

decrease in the mixing ratio of the sum of the aromatic

compounds for the 0900–1200 h PDT samples is

consistent with the mixing height data from El Monte

which showed that the morning convective boundary

layer did not exceed the height of the nocturnal

boundary layer until after 1000 h PDT each day. The

afternoon minima can be explained mainly by continu-

ing increases in mixing height with resulting dilution (see

peak afternoon mixing heights in Table 3).

Ignoring any spatial or day of the week variations in

emission sources, the ventilation index would suggest

that the highest morning anthropogenic VOC mixing

ratios would be expected on 4 August and 4 September

ARTICLE IN PRESS

Table 2

Calculated lifetimes for selected BVOCs and aromatic VOCs with respect to reaction with the OH radical, reaction with the NO3

radical, reaction with O3, and yields of methacrolein and methyl vinyl ketone from the isoprene reactions

Lifetime due to Yield from isoprene reaction with

Hydrocarbon OHa NO3b O3

c OHd NO3e O3

f

Isopreneg 1.4 h 49min 10 h

Methacrolein 4.9 hh 14 dayi 5 dayj 0.23 0.035 0.39

Methyl vinyl ketone 6.9 hh >1.1 yrk 1.1 dayj 0.33 0.035 0.16

a-Pineneg 2.6 h 5min 1.5 h

Limoneneg 49min 3min 38min

1,8-Cineole 12.5 hl 0.7 yrl >35daym

Benzenen 9.6 day >4.2 yr >14yr

m-Xylenen 6.0 h 0.5 yr >5yr

aFor a 12-h daytime average OH radical concentration of 2.0� 106 molecule/cm3.bFor a 12-h nighttime average NO3 radical concentration of 5� 108 molecule/cm3.cFor a 24-h average O3 concentration of 2.2� 1012 molecule/cm3 (B90 ppbv).dAverage of yields by Tuazon and Atkinson (1990), Paulson et al. (1992), Miyoshi et al. (1994).eKwok et al. (1996).fAschmann and Atkinson (1994).gRate constants from Calvert et al. (2000).hRate constants from Atkinson et al. (1983), Gierczak et al. (1997).iRate constant from Chew et al. (1998).jRate constants from Atkinson (1994).kRate constant from Rudich et al. (1996).lRate constants from Corchnoy and Atkinson (1990).mUpper limit to rate constant from Atkinson et al. (1990).nRate constants from Calvert et al. (2002).


when the ventilation indices (see Table 3) are at a

minimum, and the lowest morning VOC mixing ratios

on 5 August and 6 September when the ventilation

indices were maximized. Although the lowest morning

mixing ratio for the aromatic compounds was indeed

measured on 6 September when the ventilation index

was high, for the limited data set available here, the

ventilation index alone was generally not a good

predictor of morning VOC mixing ratios at Azusa.

As noted, CO can serve as a non-reactive tracer of

vehicle emissions. CO maximized in the early morning at

Azusa due to overnight and early morning traffic

emissions into a low overnight boundary layer and

decreased in the afternoon due to convective mixing and

an increased mixing depth. Thus, normalizing to CO

should attenuate diurnal variations due solely to mixing

height depth and a non-reactive species with a similar

traffic source will have a near constant ambient

concentration ratio to CO. Considering benzene because

it is the most long-lived of the aromatics (see Table 2), it

can be seen that the time profile of benzene/CO does in

fact show significantly less diurnal variation than the

sum of the aromatics (see Figs. 2 and 3).

3.1.2. Monoterpenes

Tree species have been reported to dominate mono-

terpene emissions (Geron et al., 2000), but monoter-

penes from shrubs such as sagebrush and chaparrel may

be important in some locales (Guenther et al., 1995;

Fall, 1999; Kesselmeier and Staudt, 1999). Although

conifers have monoterpenes stored in resin ducts and

shrubs may have external stores in glandular trichomes,

for both vegetation types the monoterpene emissions are

expected to occur throughout 24-h periods and to

increase with ambient temperature (Fall, 1999). The

rapid atmospheric reactions of alkene BVOCs noted

above will have an important influence on their mixing

ratios.

The monoterpene mixing ratios, expressed as the sum

of the four dominant monoterpene compounds, max-

imized in the early morning hours (see Figs. 2 and 3). In

contrast with the benzene/CO ratios, normalizing the

sum of monoterpenes to CO gave monoterpene/CO

ratios which consistently stayed at a higher level at

nighttime and showed sharp maxima at 0300–0600 h

PDT on all days. This suggests different sources and

possibly different source areas for the monoterpenes and

anthropogenic compounds such as CO and aromatic

hydrocarbons.

The results of the 158m agl back trajectories

calculated for Azusa are summarized in Table 4. The

air parcels arriving at 0600 and 0900 h PDT were taken

as representative of the 0300–0600 h PDT and 0600–

0900 h PDT sampling periods, respectively. It should be

noted that on each day the 158m agl trajectory level was

within the mixed layer, assuming that the air parcel was

over the mostly flat portion of the basin. Thus, the air

parcel paths at this level were probably representative of

the air throughout the mixed layer. If the back trajectory

for an air parcel arriving at Azusa had a path for the

prior 6 h that remained in the mostly flat portion of the

basin, the source of VOCs arriving at Azusa was

considered an ‘‘urban’’ source. Air parcel paths that

passed over ground within the foothills or mountains,

where the ground level was below about 1000m during

the prior 6h were considered to bring BVOCs from ‘‘low

mountain’’ source areas. Air parcel paths that passed

over ground above about 1000m in elevation were

considered to carry BVOCs from ‘‘high mountain’’

source areas. ‘‘Drainage’’ flow is used to describe back

trajectories with air parcel paths descending from the

elevated areas to the north of Azusa. The low mountain

ARTICLE IN PRESS

Table 3

Surface winds at Azusa, mixing heights at El Monte/Pomona, and calculated morning ventilation indices

Date Time of flow

(PDT)

Wind

direction

Average wind

speed (m/s)

Duration (h) Mixing height

at El Monte

0800–0900h

(magl)

Ventilation

index (m2/s)

Peak afternoon

mixing heights at

El Monte/Pomona

(magl)

4 August 1997 21–07 E 2.5 11 250 625

4 August 1997 08–21 SW 3.3 12 650/750

5 August 1997 22–08 E 3.5 11 275 962

5 August 1997 09–21 SW 2.9 13 600/750

6 August 1997 22–07 E-NE 1.9 10 400 760

6 August 1997 08–21 SW 3.2 14 600/650

4 September 1997 22–09 E 2.5 12 250 625

4 September 1997 10–22 SW 2.8 13 1200/1900

5 September 1997 23–08 E 1.7 10 375 638

5 September 1997 09–20 SW 3.0 12 1000/1300

6 September 1997 21–08 Variable 1.6 12 600 960

6 September 1997 09–22 SW 2.8 14 700/1000


area BVOC emissions are from mainly shrub vegetation,

and the high mountain emissions will reflect the presence

of coniferous forested areas rich in monoterpenes.

Although the low mountain terrain emissions will likely

be dominated during the daytime by isoprene emissions,

the BVOCs in the nighttime drainage flow may be

influenced by nighttime NO3 radical chemistry (dis-

cussed in detail below) and will lack fresh light-

dependent isoprene emissions (Reissell and Arey, 2001).

As shown in Table 4, trajectories for four out of the

six days showed that the air parcels arriving at Azusa at

0600 h PDT and 0900 h PDT were in the San Gabriel

Mountains six hours prior to arrival and the parcel

paths were associated with drainage flow. On 4 and 5

August and 4 and 5 September, the drainage flow was

strong and emissions from trees in the San Gabriel

forest, as well as from the shrub vegetation common to

the local hills would be transported to Azusa.

An example trajectory for these days is shown in

Fig. 4, which is the 158m agl back trajectory arriving at

Azusa at 0600 h PDT on 5 August. The trajectory shows

that the parcel was near Malibu on the morning of 4

ARTICLE IN PRESS

Fig. 4. Twenty-four hour 158m agl back trajectory beginning at Azusa, CA at 0600h PDT on 5 August 1997. UTM E and UTMN are

Universal Transverse Mercator East and North coordinates, respectively.

Table 4

Summary of air parcel paths, probable source areas and selected VOC ratios for Azusa

Date Parcel

arrival time

(PDT)

Parcel path 6 h

preceding

Probable source area

(6 h preceding)

Sampling Time

(PDT)

SMonoterpenes

benzene

MVK

MACR

4 August 1997 0600 Drainage Low and high mountain 0300–0600

4 August 1997 0900 Drainage Low and high mountain 0600–0900 0.5

5 August 1997 0600 Drainage Low and high mountain 0300–0600 0.5 0.6

5 August 1997 0900 Drainage Low and high mountain 0600–0900 0.2 2.1

6 August 1997 0600 From the East Urban and low mountain 0300–0600 0.8 1.4

6 August 1997 0900 From the East Urban and low mountain 0600–0900 0.4 2.1

4 September 1997 0600 Drainage Low and high mountain 0300–0600 0.9 1.5




6 September 1997 0600 From the West Urban 0300–0600 0.6 1.2

6 September 1997 0900 From the West Urban 0600–0900 0.6 0.8


August, eventually traveling east along the San Gabriel

Mountains before descending to Azusa in the morning

drainage flow. Although the 6–24 h parcel paths differ

on 4 and 5 August and on 4 and 5 September, the

existence and strength of the drainage flow is quite

similar. That is, from midnight to 0600 h PDT on these

four days, air was flowing into Azusa from the

mountains to the north.

On 6 August and 6 September, the parcel paths 6 h

prior to arrival at Azusa were different. On 6 August the

parcel path was from the east along the base of the San

Gabriel Mountains (parcel path not shown for this day);

therefore, the VOC source area for Azusa on 6 August is

classified as urban/low mountain. Fig. 5 shows the 158-

m agl back trajectory arriving at Azusa at 0600 h PDT

on 6 September. The parcel originated on the morning of 5

September in the Pacific Ocean, north of Santa Barbara

Island, and arrived at Azusa at 0600h PDT after traveling

east along the base of the San Gabriel Mountains. Since

the parcel path did not traverse the mountains, the VOC

source area on this day is classified as urban.

As may be seen from Table 3, all dates except 6

September had average overnight winds from the east at

Azusa. Although the trajectories generally show north-

erly drainage flow overnight, it is probable that this

drainage flow turned easterly as the air flowed into the

basin. At Glendora (see Fig. 1), which is closer to the

San Gabriel Mountains and as a result of being near

the mouth of a major canyon has more pronounced

drainage flow, all days, except 5 and 6 September, had

overnight drainage flow with winds from the north.

Consistent with the trajectory analysis, only for 6

September was there a complete lack of apparent

drainage flow as evidenced by no winds at Glendora

and variable, light winds at Azusa. Therefore, on all

days except 6 September, BVOCs emitted in the San

Gabriel Mountains are expected to have been trans-

ported during the night to Azusa.

Consistent with the generally low 0800–0900 h PDT

mixing heights (see Table 3) and predicted nighttime

drainage flows bringing monoterpenes to Azusa (see

Table 4), the monoterpene mixing ratios increased

during nighttime and maximized generally in the early

morning hours at 0300–0600 h PDT or 0600–0900 h

PDT. The lack of obvious drainage flow reaching Azusa

on 6 September and the higher mixing height recorded

on that morning are presumably reflected in the some-

what lower monoterpene maximum of B 0.8 ppbv,

compared with 1.2, 1.3, 1.5 and 1.1 ppbv for 5 and 6

August and 4 and 5 September, respectively. No

monoterpene data are available for 4 August from

0300–0600 h PDT, but the highest monoterpene sum was

measured on 4 September consistent with the low

calculated ventilation index on this date (see Table 3).

The presence of an early morning monoterpene max-

imum, although somewhat reduced, on 6 September

when no drainage flow was predicted to have occurred

may be attributable to local monoterpene emissions at

Azusa under light wind conditions accumulating in the

absence of nighttime chemical loss processes.

The ratio of the Smonoterpenes/benzene (see Table 4)

is higher for 0300–0600 h PDT than for 0600–0900 h

PDT on all mornings except that of 6 September, which

as noted, had a back trajectory that did not indicate

ARTICLE IN PRESS

Fig. 5. Twenty-four hour 158m agl back trajectory beginning at Azusa, CA at 0600 h PDT on 6 September 1997.


drainage flow. The fact that 6 August, with no apparent

drainage flow into Azusa, also had a higher Smono-

terpenes/benzene ratio for 0300–0600 h PDT than 0600–

0900 h PDT might suggest a possible influence of more

local low mountain/foothill monoterpene sources, con-

sistent with drainage flow being measured at Glendora

on this date.

3.1.3. Isoprene, methacrolein and methyl vinyl ketone

Isoprene mixing ratios (Figs. 2 and 3) were consis-

tently highest during daytime and lowest at nighttime.

Isoprene is mainly emitted by deciduous vegetation, and

emission rates are affected both by light [photosynthe-

tically active radiation (PAR)] and temperature, typi-

cally maximizing at B800 PAR and increasing with

temperature up to B40�C (Fall, 1999; Guenther, 1999).

Normalizing isoprene to CO at Azusa compensates for

the increased dilution in the afternoon and the peak

consistently observed at 1700–2000 h PDT suggests local

isoprene emissions, from for example Eucalyptus spp.,

maximized under full sunlight during this hot part of the

day. An alternative explanation would be entrainment

of isoprene-rich air resulting from vegetative emissions

at elevated locations.

MACR and MVK are atmospheric transformation

products of isoprene (see Table 2). The complex diurnal

profiles of isoprene, MACR and MVK at Azusa can be

contrasted with simultaneous measurements made on

Pine Mountain (at 1300–1400m), located in the San

Gabriel Mountains and 11 km north of Azusa. At Pine

Mountain, isoprene increased rapidly after sunrise

followed, after a lag time, by increases in MACR and

MVK. These profiles were consistently repeated each

day and were attributed to local isoprene emissions

controlled by light and temperature, and MACR and

MVK formed dominantly from daytime OH radical

reaction of isoprene. Rapid decreases in isoprene after

sunset were attributed to reaction with NO3 radicals

(Reissell and Arey, 2001). Nitrate radicals can form at

elevated sites to which NOx and O3 have been

transported from the basin during the daytime and

which then become isolated from basin NO emissions,

for example, by being located within a nighttime

elevated stable inversion layer (Lu and Turco, 1994,

1995, 1996). As discussed below, if the MACR and

MVK at Azusa are solely the product of isoprene

reactions, these must include both daytime OH radical

reactions and transport from areas where nighttime

isoprene chemistry has occurred.

3.2. Atmospheric chemistry

At Azusa during the daytime, atmospheric chemistry

will be very important in determining the concentrations

of BVOCs. As seen from Table 2, the OH radical-

initiated reaction is important and often the dominant

VOC atmospheric loss processes. The OH radical

concentration of 2� 106 radicals cm3 which was used

here to calculate lifetimes due to OH radical reaction is

based on a globally and annually averaged value (Prinn

et al., 1995, 2001; Hein et al., 1997) and daytime maxima

in September (1993) of 5–6� 106 radicals/cm3 have been

reported for Los Angeles (George et al., 1999). To

illustrate the reactivity of alkene BVOCs with NO3

radicals and O3, the lifetime calculations given in Table 2

were made using an NO3 radical concentration of

5� 108 molecules/cm3 [a value consistent with modeled

NO3 at an elevated site during SCOS97-NARSTO,

where 8 ppbv NO2 and 80 ppbv O3 were present at

sunset (Reissell and Arey, 2001)] and an O3 concentra-

tion of 90 ppbv (a 1-h average value reached at Azusa on

all six days discussed here).

High O3 concentrations will affect the alkene BVOC

lifetimes, and as can be seen from Table 4 the overall

lifetime of limonene due to daytime reaction with 2� 106

molecules/cm3 OH and 90 ppbv of O3 would be less than

a half hour. In contrast, during the evenings at Azusa

little or no chemistry occurred and therefore

monoterpenes brought to Azusa in drainage flows or

emitted locally during the night accumulated under the

nocturnal boundary layer. The O3 concentration routi-

nely dropped to low levels (p4 ppbv) each night at

Azusa, being titrated by vehicle traffic NO emissions

into the shallow nocturnal boundary layer (this also

eliminates O3-alkene reactions as a nighttime source of

OH radicals, Paulson et al., 1999). The presence of NO

also precluded significant NO3 radical concentrations

(note that NO3 radicals are not important during

the daytime because of their rapid photolysis) (Wayne

et al., 1991).

The influence of chemistry can be seen by comparing

the diurnal profile of reactive monoterpenes such as

limonene and a-pinene with long-lived species such as 1,8-

cineole (emitted perhaps from local Eucalyptus trees)

[refer to the bottom panels of Figs. 2 and 3 for this and

the following discussions]. At Azusa, the highest mono-

terpene mixing ratios were measured for limonene and a-pinene—in the early morning hours. There were rapid

decreases in a-pinene and limonene before noon, but less

pronounced decreases in 1,8-cineole. Cineole and another

long-lived BVOC, camphor, showed profiles very similar

to one another, with less rapid afternoon decreases and

less pronounced day-night differences than the more

reactive monoterpenes (Reissell and Arey, 2001).

The limonene and a-pinene mixing ratios generally

followed one another, although limonene stayed at a

higher level during daytime, despite its higher reactivity

(see Table 2). This was particularly apparent in

September (Fig. 3). Very high limonene mixing ratios

(up to 3.8 ppbv) were observed on two mornings during

SCOS97-NARSTO intensive sampling periods not dis-

cussed here (Reissell and Arey, 2001), and it may be that

ARTICLE IN PRESSA. Reissell et al. / Atmospheric Environment 37 Supplement No. 2 (2003) S181–S196 S191

local, and likely anthropogenic, limonene emissions

occur near Azusa.

The reaction rate of m-xylene (the most reactive of the

four C2-benzenes) with the OH radical is about twenty

times that of benzene (Table 2). Assuming that traffic is

the main source of these two anthropogenic aromatic

compounds, a decrease in the m-xylene/benzene ratio

suggests an ‘‘aged’’ air mass (see lower left panels of

Figs. 2 and 3). At Azusa this ratio was lower during

daytime and generally lowest between 1200–1500 h PDT

when the inclusion of aged air from aloft into the rising

mixed layer could account for the lower m-xylene/

benzene ratio.

This ratio would also decrease if the rate of oxidation

of m-xylene at Azusa was significant compared to the

rate of its emission. If there were no emissions at Azusa

after the morning, about 2 h reaction with an OH radical

concentration of 6� 106 molecules/cm3 [as noted pre-

viously, the reported maximum in Sept. 1993 (George

et al., 1999)] would result in the observed factor of B3

decrease in the m-xylene/benzene ratio. Fresh emissions

from the continual traffic at Azusa (with its higher m-

xylene/benzene ratio) would tend to increase the ratio.

Thus, although the higher oxidation rate at midday

plays a role in altering the m-xylene/benzene ratio, it

seems unlikely to be the sole factor.

3.2.1. Isoprene and reaction product ratios

The relationship between isoprene and its atmospheric

transformation products MACR and MVK changes

with the type of chemistry occurring. Data collected

simultaneously at an elevated site on Pine Mountain,

located 11 km north of Azusa (sampling at B1350m),

where strong local isoprene sources were present

(isoprene maximum 2 ppbv), was consistent with day-

time OH radical reaction controlling the MACR and

MVK formation. As the isoprene mixing ratio increased

during the day, its major loss process was by reaction

with the OH radical producing MACR and MVK

(Table 2). Hydroxyl radical reaction was the major loss

process for MACR and MVK as well, and considering

only OH radical-initiated photooxidation the ratio of

(MACR+MVK)/isoprene will increase approaching an

upper limit steady-state value of 2.4 (see Reissell and

Arey, 2001). Near an isoprene emission source, or before

reaching steady-state, this ratio will be less than the

steady-state value. From the generally greater than

steady-state values of the (MACR+MVK)/isoprene

ratio at Azusa as seen in Figs. 2 and 3 (bottom right

panels) it is clear that local isoprene emission and

reaction could not account for the MACR and MVK at

Azusa, expect perhaps in the late afternoons. Thus, if

biogenic, i.e., arising from isoprene, the early morning

MACR and MVK at Azusa must have non-local

sources, which allowed nighttime chemistry to influence

the ratio of (MACR+MVK)/isoprene.

Nighttime NO3 radical reaction with isoprene will

rapidly deplete the isoprene present, leaving the MACR

and MVK mixing ratios largely unchanged (note the

equal but low yields of MACR and MVK from the NO3

radical reaction, see Table 2) . Consistent with nighttime

NO3 reaction with isoprene, at Pine Mountain at night

the ratio of (MACR+MVK/isoprene) increased dra-

matically (maxima B60 for August and B30 for

September) and the MVK/MACR ratios changed little

(Reissell and Arey, 2001). In contrast to the NO3 radical

reaction with isoprene, changes in the nighttime

(MACR+MVK)/isoprene ratio due to O3 reaction with

isoprene would result in changes to the MVK/MACR

ratio because the yield ratio from the O3 reaction is 0.4

(see Table 2) and the yield ratio from the OH reaction is

1.4 (approaching 2.1 at steady-state).

The (MACR+MVK)/isoprene ratio was consistently

high at Azusa during the nighttime and maximized at

0300–0600 h PDT. These high ratios indicate that the

MACR and MVK at Azusa were transported from areas

where the isoprene had been reacted with NO3 and/or

O3. The MVK/MACR ratios given in Table 4 for the

0300–0600 h PDT and 0600–0900 h PDT samples when

the ratio (MACR+MVK)/isoprene was high are con-

sistent with isoprene loss mainly by NO3 reaction

(MVK/MACR from 1.4 to 2.1, reflecting their forma-

tion from daytime OH radical reaction of isoprene) with

the MVK/MACR valueso1.4 suggesting a contribution

of O3 reaction to the nighttime isoprene losses. The fact

that the MVK/MACR ratios measured for the 0300–

0600 h PDT and 0600–0900 h PDT samples on a given

day were not the same is consistent with the wind

changing from generally east at night to southwest

sometime between 0800 and 1000 h PDT.

The occurrence of nighttime NO3 chemistry at

elevated locations during the SCOS97-NARSTO study

was supported by the BVOC reactions observed at Pine

Mountain and Mount Baldy (located 25 km NE of

Azusa; sampling at B1200 m elevation) and by

measurements of O3 at Pine Mountain and of O3 and

NO2 at sunset on Mount Baldy (Reissell and Arey,

2001). Attributing the high (MACR + MVK)/isoprene

ratio at Azusa to nighttime NO3 chemistry depleting

isoprene at elevated sites, followed by transport of

MACR and MVK to Azusa requires daytime upslope

flow (to bring NOx and O3 to the elevated sites where

isoprene is being emitted) and nighttime drainage flow

into Azusa.

As seen from Table 4, on all days except 6 September

the CALMET model trajectories predicted that BVOCs

from low mountain areas were transported to Azusa

overnight. Back trajectory analyses showed previous-

day afternoon and evening flow into the mountains for

air parcels arriving at Azusa on 4–6 August and on 5

September. Flow was up the canyons just north of

Azusa for air parcels arriving at Azusa on 4 August and


5 September and up the west side of the San Gabriel

Mountains (see, for example, Big Tujunga Canyon in

Fig. 4) for air parcels arriving on 5 and 6 August.

However, as shown in Fig. 5, the air arriving at Azusa

on 6 September is predicted not to have spent any time

in the San Gabriel Mountains and was over the Pacific

the prior day. For the afternoon of 3 September, the

trajectories indicated that winds transported air from

the high desert northeast of the mountains, into the San

Gabriel Mountains, and then downslope to Azusa on

the morning of 4 September. Thus, trajectory analyses

show mountain influence for all these mornings, except

for 6 September.

The apparent inconsistency in the meteorological

model results and the high early morning ratio of

(MACR+MVK)/isoprene on 6 September, i.e. the lack

of drainage flow in the early morning on 6 September,

may be because the CALMET model does not capture

local mountain effects under these low wind speed

conditions. Table 3 shows that afternoon mixing heights

on 4–6 August, although higher than during the early

morning hours, remained below about 600 to 750m agl

throughout the day at El Monte and Pomona. This

indicates that there was a strong inversion overhead with

very little vertical ventilation of pollutants on each of

these days at these locations, and probably at Azusa as

well. However, it has previously been shown (Lu and

Turco, 1994–1996) that in the Los Angeles basin, the

presence of low and high mountains results in upslope

mountain winds that carry air from the basin to

elevations above the mixed layer. As noted in Table 3,

on all days sustained southwesterly winds occurred

during the day at Azusa and these winds and heating of

the southern slopes of the hills and mountains north of

Azusa are expected to result in upslope flows, which

would transport NOx; ozone and anthropogenic VOCs

from the basin. Consistent with the existence of upslope

flows, ozone maxima were measured each day on Pine

Mountain (at 1300–1400m elevation) which generally

peaked about an hour later than at Azusa and afternoon

mixing ratios of anthropogenic tetrachloroethene

reached B70% of those simultaneously measured at

Azusa (Reissell and Arey, 2001). Therefore, because

most of the isoprene emissions are expected to occur

from the lower elevation shrub vegetation it seems likely

that local upslope flows and drainage flows from the

close-by foothills may be responsible for the early

morning MACR and MVK at Azusa, even on 6

September when the winds were very light and variable

and there was no demonstrated drainage flow.

4. Conclusions

At Azusa, CA during the 4–6 August and 4–6

September intensive sampling periods of SCOS97-

NARSTO, generally southwesterly winds prevailed

during daytime and easterly winds during nighttime.

The height of the mixed layer was at a minimum at night

and in the early morning and peaked during daytime.

Trajectory and surface wind analysis for the six intensive

sampling days indicated that, on all days except 6

September, drainage flow from the mountains at night-

time and early morning affected the BVOCs measured at

Azusa. During daytime, concentrations of the com-

pounds at Azusa were governed by emissions, reactions

with OH radicals and O3, transport by generally

southwesterly flows, convective mixing and dilution

within a rising mixed layer, as well as possible

entrainment of air from the residual layers aloft into

the rising mixed layer. During the night, NO emissions

at Azusa precluded nighttime chemistry and VOCs and

BVOCs accumulated under the low nighttime boundary

layer.

The monoterpene mixing ratios maximized in the

early morning hours and the monoterpene/CO ratios

showed sharp maxima at 0300–0600 h PDT on all days.

In contrast, normalization of benzene to CO diminished

its diurnal variation, consistent with vehicle traffic as

the source for these two long-lived anthropogenic

compounds.

Local sources for isoprene at Azusa were indicated by

the pronounced maxima in the isoprene/CO mixing

ratios occurring at 1700–2000 h PDT. Another possible

rationale for the high isoprene in the afternoon is

emissions from the foothills and mountain slopes mixing

into the deepening mixed layer. This is consistent with

the high daytime isoprene mixing ratios measured, for

example, at Pine Mountain. During daytime, limonene

mixing ratios at Azusa stayed at a higher level than a-pinene, although the lifetime of limonene is expected to

be shorter than that of a-pinene, suggesting probable

local anthropogenic sources for limonene.

Substantial early morning MACR and MVK mixing

ratios (and high (MACR+MVK)/isoprene ratios)

measured at Azusa were consistent with drainage flow

from elevated mountain areas which had received NOx

emissions transported from the urban basin by upslope

flows under consistent daytime southwesterly winds.

Drainage flow from the high elevations is expected to be

depleted in a-pinene, limonene and isoprene due to

reactions with NO3 radicals. Such rapid alkene BVOC

depletions were observed at B1300–1400m elevation on

Pine Mountain in samples collected simultaneously with

those described here (Reissell and Arey, 2001). As the air

flows over the foothills at lower elevations, continuing

emissions would supply monoterpenes (but not light-

dependent isoprene) into the nighttime drainage flow

which then travels into basin areas, such as Azusa,

where further nighttime reactions are precluded by NO

emissions. The high ratio of (MACR+MVK)/isoprene

even on 6 September, the single day without apparent


drainage flow, may indicate that the CALMET meteor-

ological model did not capture local mountain effects

under the low wind speed conditions present on this day.

The presence of an early morning monoterpene max-

imum on 6 September, although reduced in comparison

with those of other mornings, suggests that in the

absence of nighttime chemical loss processes local

monoterpene emissions can accumulate to significant

levels.

Because of the high reactivity of the BVOCs, a

thorough understanding of the interplay of basin NOx

emissions reaching elevated areas and of BVOCs and

their reaction products returning in drainage flows will

require more time-resolved measurements than made

during SCOS97-NARSTO. It would be advantageous to

simultaneously conduct, with high time resolution,

measurements of BVOCs, their major reaction products,

anthropogenic VOCs, as well as meteorological para-

meters both in the Los Angeles Basin and at elevated

sites.

Acknowledgements

The SCOS97-NARSTO BVOC data collection de-

scribed in this manuscript was funded by the California

Air Resources Board through contract 95–309 and was

made possible through the logistical support of Rudy

Eden of the South Coast Air Quality Management

District and Bart Croes, Randy Pasek and Ash Lashgari

of the California Air Resources Board. A.R. gratefully

acknowledges support from the Maj and Tor Nessling

Foundation, the Helsingin Sanomat Centennial Foun-

dation, the Ella and Georg Ehrnrooth Foundation and

the Jenny and Antti Wihuri Foundation. J.A. acknowl-

edges support from US Department of Energy Grant

No. DE-FG03-01ER63095 and the University of Cali-

fornia Agricultural Experiment Station. C.M. acknowl-

edges Jason Roney of Sonoma Technology, Inc. who

assisted in performing the CALMET model runs and

production of the trajectories. C.M. also acknowledges

the numerous organizations who collected the upper-air

radar profiler wind data and the surface meteoro-

logical data, with special thanks to the National Oceanic

and Atmospheric Administration’s Environmental

Technology Laboratory for processing the upper-air

wind data.

References

Aschmann, S.M., Atkinson, R., 1994. Formation yields of

methyl vinyl ketone and methacrolein from the gas-phase

reaction of O3 with isoprene. Environmental Science and

Technology 28, 1539–1542.

Atkinson, R., 1994. Gas-phase tropospheric chemistry of

organic compounds. Journal of Physical and Chemical

Reference Data. Monograph 2, 1–216.

Atkinson, R., 1997. Gas-phase tropospheric chemistry of

volatile organic compounds: 1 alkanes and alkenes. Journal

of Physical and Chemical Reference Data 26, 215–290.

Atkinson, R., 2000. Atmospheric chemistry of VOCs and NOx.

Atmospheric Environment 34, 2063–2101.

Atkinson, R., Aschmann, S.M., Pitts Jr., J.N., 1983. Kinetics of

the gas-phase reactions of OH radicals with a series of a,b-unsaturated carbonyls at 29972K. International Journal of

Chemical Kinetics 15, 75–81.

Atkinson, R., Hasegawa, D., Aschmann, S.M., 1990. Rate

constants for the gas-phase reactions of O3 with a series of

monoterpenes and related compounds at 29972K. Inter-

national Journal of Chemical Kinetics 22, 871–887.

Biesenthal, T.A., Wu, Q., Shepson, P.B., Wiebe, H.A., Anlauf,

K.G., Mackay, G.I., 1997. A study of relationships between

isoprene, its oxidation products, and ozone, in the

Lower Fraser Valley, BC. Atmospheric Environment 31,

2049–2058.

Calogirou, A., Larsen, B.R., Brussol, C., Duane, M., Kotzias,

D., 1996. Decomposition of terpenes by ozone during

sampling on Tenax. Analytical Chemistry 68, 1499–1506.

Calvert, J.G., Atkinson, R., Kerr, J.A., Madronich, S.,

Moortgat, G.K., Wallington, T.J., Yarwood, G., 2000.

The Mechanisms of Atmospheric Oxidation of the Alkenes.

Oxford University Press, New York, NY, 552pp.

Calvert, J.G., Atkinson, R., Becker, K.H., Kamens, R.M.,

Seinfeld, J.H., Wallington, T.J., Yarwood, G., 2002. The

Mechanisms of Atmospheric Oxidation of the Aromatic

Hydrocarbons. Oxford University Press, New York, NY,

556pp.

CARB, 2000. California Air Resources Board, Research

Division, Sacramento, CA, SCOS97, NARSTO, Data Vol.

1, Ozone Study, RD-2000-001.

Chameides, W.L., Lindsay, R.W., Richardson, J., Kiang, C.S.,

1988. The role of biogenic hydrocarbons in urban

photochemical smog: Atlanta as a case study. Science 241,

1473–1475.

Chameides, W.L., Fehsenfeld, F., Rodgers, M.O., Cardelino,

C., Martinez, J., Parrish, D., Lonneman, W., Lawson, D.R.,

Rasmussen, R.A., Zimmerman, P., Greenberg, J., Mid-

dleton, P., Wang, T., 1992. Ozone precursor relationships in

ambient atmosphere. Journal of Geophysical Research 97,

6037–6055.

Chew, A.A., Atkinson, R., Aschmann, S.M., 1998. Kinetics

of the gas-phase reactions of NO3 radicals with a series of

alcohols, glycol ethers, ethers and chloroalkenes. Journal of

the Chemical Society Faraday Transactions 94, 1083–1089.

Corchnoy, S.B., Atkinson, R., 1990. Kinetics of the gas-phase

reactions of OH and NO3 radicals with 2-carene, 1,8-

cineole, p-cymene, and terpinolene. Environmental Science

and Technology 24, 1497–1502.

Fall, R., 1999. Biogenic emissions of volatile organic com-

pounds from higher plants. In: Hewitt, C.N. (Ed.), Reactive

Hydrocarbons in the Atmosphere. Academic Press, San

Diego, pp. 41–96.

Fehsenfeld, F.C., Calvert, J., Fall, R., Goldan, P., Guenther,

A.B., Hewitt, C.N., Lamb, B., Liu, S., Trainer, M.,

Westberg, H., Zimmerman, P., 1992. Emissions of volatile


organic compounds from vegetation and the implications

for atmospheric chemistry. Global Biochemical Cycles 6,

389–430.

Fuentes, J.D., Lerdau, M., Atkinson, R., Baldocchi, D.,

Bottenheim, J.W., Ciccioli, P., Lamb, B., Geron, C., Gu,

L., Guenther, A., Sharkey, T.D., Stockwell, W., 2000.

Biogenic hydrocarbons in the atmospheric boundary layer:

a review. Bulletin of the American Meteorological Society

81, 1537–1575.

George, L.A., Hard, T.M., O’Brien, R.J., 1999. Measurement

of free radicals OH and HO2 in Los Angeles smog. Journal

of Geophysical Research 104, 11643–11655.

Geron, C., Rasmussen, R., Arnts, R.R., Guenther, A., 2000. A

review and synthesis of monoterpene speciation from forests

in the United States. Atmospheric Environment 34,

1761–1781.

Gierczak, T., Burkholder, J.B., Talukdar, R.K., Mellouki, A.,

Barone, S.B., Ravishankara, A.R., 1997. Atmospheric fate

of methyl vinyl ketone and methacrolein. Journal of

Photochemistry and Photobiology A: Chemistry 110, 1–10.

Griffin, R.J., Cocker III, D.R., Seinfeld, J.H., Dabdub, D.,

1999. Estimate of global atmospheric aerosol from oxida-

tion of biogenic hydrocarbons. Geophysical Research

Letters 26, 2721–2724.

Guenther, A., 1999. Modeling biogenic volatile organic

compound emissions to the atmosphere. In: Hewitt, C.N.

(Ed.), Reactive Hydrocarbons in the Atmosphere. Academic

Press, San Diego, pp. 97–118.

Guenther, A., Hewitt, C.N., Erickson, D., Fall, R., Geron, C.,

Graedel, T., Harley, P., Klinger, L., Lerdau, M., McKay,

W.A., Pierce, T., Scholes, B., Steinbrecher, R., Tallamraju,

R., Taylor, J., Zimmerman, P., 1995. A global model of

natural volatile organic compound emissions. Journal of

Geophysical Research 100, 8873–8892.

Guenther, A., Geron, C., Pierce, T., Lamb, B., Harley, P., Fall,

R., 2000. Natural emissions of non-methane volatile organic

compounds, carbon monoxide, and oxides of nitrogen

from North America. Atmospheric Environment 34,

2205–2230.

Hein, R., Crutzen, P.J., Heimann, M., 1997. An inverse

modeling approach to investigate the global atmospheric

methane cycle. Global Biogeochemical Cycles 11, 43–76.

Hoffmann, T., Odum, J.R., Bowman, F., Collins, D., Klockow,

D., Flagan, R.C., Seinfeld, J.H., 1997. Formation of organic

aerosols from the oxidation of biogenic hydrocarbons.

Journal of Atmospheric Chemistry 26, 189–222.

Kavouras, I.G., Mihalpoulos, N., Stephanou, E.G., 1999.

Secondary organic aerosol formation vs primary organic

aerosol emission: in situ evidence for the chemical coupling

between monoterpene acidic photooxidation products and

new particle formation over forests. Environmental Science

and Technology 33, 1028–1037.

Kesselmeier, J., Staudt, M., 1999. Biogenic volatile organic

compounds (VOC): an overview on emission, physio-

logy and ecology. Journal of Atmospheric Chemistry 33,

23–88.

Kwok, E.S.C., Aschmann, S.M., Arey, J., Atkinson, R., 1996.

Product formation from the reaction of the NO3 radical

with isoprene and rate constants for the reactions of

methacrolein and methyl vinyl ketone with the NO3 radical.

International Journal of Chemical Kinetics 28, 925–934.

Lu, R., Turco, R.P., 1994. Air pollutant transport in a coastal

environment—I. Two-dimensional simulations of sea-breeze

and mountain effects. Journal of Atmospheric Sciences 51,

2285–2308.

Lu, R., Turco, R.P., 1995. Air pollutant transport in a coastal

environment—II. Three-dimensional simulations over Los

Angeles Basin. Atmospheric Environment 29, 1499–1518.

Lu, R., Turco, R.P., 1996. Ozone distribution over the Los

Angeles Basin: three-dimensional simulations with the

SMOG model. Atmospheric Environment 30, 4155–4176.

MacDonald, C.P., Barnett, A.N., Dye, T.S., Nguyen, D.T.,

Knoderer, C.A., Roberts, P.T., Baxter, R.A., Weber, B.L.,

2002. Processing and validation of data collected by radar

wind profilers, radio acoustic sounding systems, and sodars

during the 1997 Southern California Ozone Study. Prepared

for California Air Resources Board, Sacramento, CA and

South Coast Air Quality Management District, Diamond

Bar, CA by Sonoma Technology, Inc., Petaluma, CA,

Parsons Corporation, Pasadena, CA, and National Oceanic

and Atmospheric Administration, Environmental Technol-

ogy Laboratory, Boulder, CO, STI-99752A/B-2151-DFR,

February.

Miyoshi, A., Hatakeyama, S., Washida, N., 1994. OH radical-

initiated photooxidation of isoprene: an estimate of global

CO production. Journal of Geophysical Research 99,

18779–18787.

M .uller, J.-F., 1992. Geographical distribution and seasonal

variation of surface emissions and deposition velocities of

atmospheric trace gases. Journal of Geophysical Research

97, 3787–3804.

Paulson, S.E., Flagan, R.C., Seinfeld, J.H., 1992. Atmospheric

photooxidation of isoprene part I: the hydroxyl radical and

ground state atomic oxygen reactions. International Journal

of Chemical Kinetics 24, 79–101.

Paulson, S.E., Chung, M.Y., Hasson, A.S., 1999. OH radical

formation from the gas-phase reaction of ozone with

terminal alkenes and the relationship between structure

and mechansim. Journal of Physical Chemistry 103,

8125–8138.

Piccot, S.D., Watson, J.J., Jones, J.W., 1992. A global

inventory of volatile organic compound emissions from

anthropogenic sources. Journal of Geophysical Research

97, 9897–9912.

Prinn, R.G., Weiss, R.F., Miller, B.R., Huang, J., Alyea, F.N.,

Cunnold, D.M., Fraser, P.J., Hartley, D.E., Simmonds,

P.G., 1995. Atmospheric trends and lifetime of CH3CCl3and global OH concentrations. Science 269, 187–192.

Prinn, R.G., Huang, J., Weiss, R.F., Cunnold, D.M., Fraser,

P.J., Simmonds, P.G., McCulloch, A., Harth, C., Salameh,

P., O’Doherty, S., Wang, R.H.J., Porter, L., Miller, B.R.,

2001. Evidence for substantial variations of atmospheric

hydroxyl radicals in the past two decades. Science 292,

1882–1888.

Reissell, A., Arey, J., 2001. Biogenic volatile organic com-

pounds at Azusa and elevated sites during the 1997

Southern California Ozone Study. Journal of Geophysical

Research 106, 1607–1621.

Rudich, Y., Talukdar, R.K., Fox, R.W., Ravishankara, A.R.,

1996. Rate coefficients for reactions of NO3 with a few

olefins and oxygenated olefins. Journal of Physical Chem-

istry 100, 5374–5381.


SCAQMD, 2001. South Coast Air Quality Management

District, Diamond Bar, CA.

Scire, J.S., Robe, F.R., Fernau, M.E., Yamartino, R.J., 1999. A

User’s Guide for the CALMET Meteorological Model

(Version 5.0). Earth Tech Inc., Concord, MA.

Starn, T.K., Shepson, P.B., Bertman, S.B., White, J.S., Splawn,

B.G., Riemer, D.D., Zika, R.G., Olszyna, K., 1998.

Observations of isoprene chemistry and its role in ozone

production at a semirural site during the 1995 Southern

Oxidant Study. Journal of Geophysical Research 103,

22425–22435.

Trainer, M., Hsie, E.Y., McKeen, S.A., Tallamraju, R., Parrish,

D.D., Fehsenfeld, F.C., Liu, S.C., 1987a. Impact of natural

hydrocarbons on hydroxyl and peroxy radicals at a remote

site. Journal of Geophysical Research 92, 11879–11894.

Trainer, M., Williams, E.J., Parrish, D.D., Buhr, M.P., Allwine,

E.J., Westberg, H.H., Fehsenfeld, F.C., Liu, S.C., 1987b.

Models and observations of the impact of natural hydro-

carbons on rural ozone. Nature 329, 705–707.

Tuazon, E.C., Atkinson, R., 1990. A product study of the gas-

phase reaction of isoprene with the OH radical in the

presence of NOx. International Journal of Chemical

Kinetics 22, 1221–1236.

Wayne, R.P., Barnes, I., Biggs, P., Burrows, J.P., Canosa-Mas,

C.E., Hjorth, J., Le Bras, G., Moortgat, G.K., Perner, D.,

Poulet, G., Restelli, G., Sidebottom, H., 1991. The nitrate

radical: physics, chemistry, and the atmosphere. Atmo-

spheric Environment 25A, 1–203.

Went, F.W., 1960. Blue hazes in the atmosphere. Nature 187,

641–643.

World Meteorological Organization, 1995. Scientific Assess-

ment of Ozone Depletion; 1995. Global Ozone Research

and Monitoring Project, Report No. 37, Geneva, Switzer-

land (Chapter 2).


characterization of biogenic volatile organic compounds and meteorology at azusa during the...

Documents