1

North American North American Pollutant ExportPollutant Export due to due to

Anthropogenic Emissions and LightningAnthropogenic Emissions and Lightning

Dale Allen, Ken Pickering, Georgiy Stenchikov, Ed Hyer

Student SeminarNovember 12, 2008

MM aa tt uu ss M M aa rr tt ii nn ii

2

What am I going to talk about?

• Motivation for our study: radiative forcing

• Air quality and long-range transport

• Impact of anthro emissions, and lightning

• Challenges to calculate the upper tropospheric NOx so important for long-range transport

3

4

Tropospheric ozoneis the third most important

greenhouse gas.

Our calculation: UMDCTM, Ming-Dah Chou’s RTMRadiative Forcing due to O3 resulted from anthropogenic emissions 2002

5

For comparison, IPCC 2007:

“Global present-day RFdue to tropospheric ozone

is 0.35 Wm-2.”

Our calculation: UMDCTM, Ming-Dah Chou’s RTMRadiative Forcing due to O3 resulted from anthropogenic emissions 2004

6

What is new in this study?

• What is the impact of NOx emissions (from power plants and lightning) on tropospheric ozone and the associated radiative forcing as a convenient measure of pollutant long-range export?

• Are meteorology effects (lightning, convection) more influential than emission effects to long-range export? Important in changing climate.

• Testing new lightning parameterization scheme with constraints to observations: space-based OTD/LIS, ground-based lightning detection network: NLDN

• We would like to avoid using the lightning climatology – LNOx not being injected into the model at the same times and locations as where model convection occurs

• This study is not complete.

7

Methodology• NOx (NO + NO2) major O3 precursors <- fossil fuel combustion, lightning,

soils, biomass burn, aircraft

Anthropogenic NOx sources

• NOx SIP Call: NOx emissions reduced by 50% (Frost et al. 2006)

• EPA issued Clean Air Interstate Rule March 2005 - 60% 2003/2015 reductions - reduce the impact on surface AQ (Kim et al. 2006)

• Emission Database for Global Atmospheric Research (EDGAR):U.S. power generation accounted for one quarter (4.8 Tg NO2) of national NOx emissions (19.4 Tg NO2) which are dominated by mobile sources (road transport 6.3 Tg, international shipping 1.9 Tg and air transport 0.9 Tg of NO2).

In our study we use: state of the art CEMS (Continuous Emission Monitoring) monthly emission inventory (very accurate) over the US for NOx power plants

8

• Lightning NOx

• Abundance of water vapor and surface heating

• Warmer climate may lead to increases in lightning activity

• Simulating lightning NOx with satellite and in-situ obs is difficult:

esp. spatial distribution of flashes (Allen, Pickering 2002).• We use new LP (based on upward cloud mass flux) with constraints to

obs

• Models used

• The UMD chemistry transport model - tropospheric chemical mechanism (Park et al. 2004) and is driven by fields from the GEOS-4 DAS.- We use event-specific biomass burning emissions (Kasischke et al.2005, van der Werf et al. 2006)

• Radiative transfer model (Chou et al. 1995)

Methodology

9

Meteorological Effects(temperature and moisture parameters)

In Godowitch et al. (2007),meteorology has greater impact than emission changeson Air Qualityover the north part ofOhio River Valley!

(20-80 % NOx reduction)(3-5°C colder temp)

10

Ozone difference

Improved Air Quality (summer 2004 vs 2002)

11

Improved Air Quality (summer 2004 vs. 2002)

Day of year

12

Note:

• N American anthropogenic emissions contributed ~40 ppbV to 8-hr max O3 in UMD-CTM during 2004. Data show improved AQ between 2002 and 2004.

• Emission reductions and a cooler, wetter summer contributed to lower 8-hr max. O3 in 2004 than 2002

• Upper troposphere has much stronger lightning signal than the surface

• Main lightning regions are North of Gulf of Mexico, AZ, AL, etc. not Ohio River Valley

13

SCIAMACHY space-based observation

14

Reminder

• Lightning NOx signal from SCIAMACHY is weak, comparable to the measurement uncertainty for tropospheric NO2 (0.5e15 molec NO2 cm-2)

• Large uncertainty for cloudy scenes – little consequence, since long upper tropospheric NOx lifetime 5-10 days (clouds <-> lightning)

• Higher measurement sensitivity to NO2 in the lower troposphere

• Definition of tropopause

• Major challenge in interpreting satellite obs of tropospheric column is ambiguity in the altitude of gas, dependent on a priori NO2 profile (from a model)

• More accurate retrieval is needed: Martin et al. 2007

15

• Surface O3 – air quality – importance of anthropogenic emissions

• Upper troposphere O3 – climate forcing – importance of lightning

• In 2004 better air quality (at the sfc)!

• In spite of NOx reductions and colder sfc temperatures, radiative forcing due to tropospheric ozone was greater in summer 2004 than in 2002!

• Tropo O3 is a GHG. UT has much stronger influence on sfc radiative fluxes (than polluted boundary layer).

Air Quality -> Long-range transport

16

Total flashrateIC (intracloud) + CG (cloud to ground)

Day of year

National Lightning Detection Network (NLDN) observes Cloud-to-Ground (CG)

flashes which are then multiplied by climatological IC:CG (Z) ratio

17

Total flash rateIC (intracloud) + CG (cloud to ground)

Day of year

Summer US lightning flashrate isone half ofone half of

what’s over the global flashrate:44 flashes / second

NLDN*Z

18

Adjusted IC:CG ratios for June

IC:CG ratios for June, Boccippio et al. 2001

Our adjustment:1.exclude offshore high-values2. smooth some more3. interpolate

Note:1. dependence on altitude (anti-correlated)2. high anomaly CO3.CA and New England anomaly

We are not confident about anomaly 3

19

• needs to be consistent with parameterized convection

1) Flash rate parameterization

2) Average NO production per flash

3) Vertical distribution (Pickering et al. 1998)

cloud top height, convective precipitation rate, upward cloud mass flux

Lightning parameterization

20

Our lightning parameterization

• Combining NLDN (Cummins et al., 1998) flash rates with climatological IC/CG ratios (Boccippio et al., 2001), it is possible to estimate total U.S. flash rates.

total flash rate is proportional to (zmmu – threshold)**2

• The lightning flashes are further scaled for each month to match:

1. OTD/LIS (climatology),

2. NLDN CG (year specific) * Z (IC:CG climatology)

and 44 flashes/second globally – consistent with OTD/LIS climatology (Christian et al. 2003)- 240 moles NO/flash everywhere (close to Huntrieser et al 2007)

- 480 moles NO/flash in midlatitudes (close to Ott et al. 2008 – constraint by anvil aircraft obs)

• 500 used in Hudman et al. 2007 showed better agreement with aircraft obs – however it was still low!

21

Constraining total flashrates to OTD/LIS, NLDN*Z

OTD / LISclimatology

NLDN * Z(Z = IC / CG)

Total flashrate per 2x2.5 grid box per minuteUpdraft mass flux

[Pa s-1] Input forUMDCTM

22

Constraining total flashrates to OTD/LIS, NLDN*Z

OTD / LISclimatology

NLDN * Z(Z = IC / CG)

Updraft mass flux

[Pa s-1]intermediate

step

Input forUMDCTM

23

Constraining total flash rates to OTD/LIS, NLDN*Z

OTD / LISclimatology

NLDN * Z(Z = IC / CG)

Updraft mass flux

[Pa s-1]intermediate

step

Input forUMDCTM

Note a large difference between

LIS/OTD and NLDN*Z field

24

OBS

25

OBS

26

Concluding remarks: NA pollutant export

• To investigate NA pollutant export, emission inventory has to be as accurate as possible, we are doing the difference (with anthro CTM run – w/o anthro run)

• Important role plays also the lightning NOx (longer chemical lifetimes aloft and greater wind speeds can then lead to significant large-scale transport)

• First look showed that the RF (as convenient measure of pollutant export) was interestingly larger in summer 2004 than in summer 2002.

- stronger convection in 2004 ?? (zmmu+hketa significantly larger only in May – not shown), pollutant transport to UT- enhanced lightning NOx production ?? (due to deep convection, instability)

?? both lightning and convection is parameterized, we only tune LP since we have observations available (NLDN, OTD/LIS)

- enhanced forest fires over Canada and Alaska 2004, more UT O3 (Pfister et al. 2005)

• What’s next?

27

What’s next?• Is the use of Z ratio climatology reasonable (gives high total flash rates)??

• Z ratios are based on OTD/LIS – years 1995-1999. How large is the interannual variability in OTD/LIS data??

• Should be Z ratio climatology updated – should we spend the money for the new instrument (currently LIS observes lightning only in 35 degrees South and 35 degrees North latitude)?? Recall that based on the current Z ratio climatology: in the summer half of the lightning occurs over the US!!

• Decide what to use in order to constrain the model calculated total flash rates (model uses cloud mass flux from reanalyzed metfields)

• Look directly at NO, NOx INTEX aircraft profiles rather than at ozone-sondes profiles

• Separate the individual signals: meteorology (lightning), anthro emissions (‘cross’ simulations’)

• Recalculate the RF fields