mark green and dave dubois desert research institute
DESCRIPTION
Estimating local versus regional contributions to tropospheric ozone: An example case study for Las Vegas. Mark Green and Dave DuBois Desert Research Institute. The Problem. - PowerPoint PPT PresentationTRANSCRIPT
Estimating local versus Estimating local versus regional contributions to regional contributions to tropospheric ozone: An tropospheric ozone: An
example case study for Las example case study for Las VegasVegas
Mark Green and Dave DuBoisMark Green and Dave DuBois
Desert Research InstituteDesert Research Institute
The ProblemThe Problem With new 8-hour ozone standard of 75 ppb With new 8-hour ozone standard of 75 ppb
and tendency of polluted air to affect and tendency of polluted air to affect downwind areas, local versus transported downwind areas, local versus transported pollutant contributions to ozone is importantpollutant contributions to ozone is important
Monitoring concentrated in urban areas and Monitoring concentrated in urban areas and large geographic areas of the southwestern large geographic areas of the southwestern US may exceed the new standards but US may exceed the new standards but sufficient data does not exist to define the sufficient data does not exist to define the areas exceeding standardsareas exceeding standards
How do we even know where to monitor with How do we even know where to monitor with limited resources to define the areas of high limited resources to define the areas of high concentrations?concentrations?
Use existing monitoring data, EI’s, and Use existing monitoring data, EI’s, and Chemical Transport Models to help design Chemical Transport Models to help design expanded monitoring network neededexpanded monitoring network needed
This presentationThis presentation We present some results of analysis of local We present some results of analysis of local
versus regional contributions to ground-level versus regional contributions to ground-level ozone in Las Vegas done in support of the Clark ozone in Las Vegas done in support of the Clark County Regional Ozone and Precursors Study County Regional Ozone and Precursors Study (CCROPS)(CCROPS)
We demonstrate some methodologies that We demonstrate some methodologies that might be useful elsewheremight be useful elsewhere
Disclaimer/Excuse- we were paid by Clark Disclaimer/Excuse- we were paid by Clark County, Nevada only to collect upper air data County, Nevada only to collect upper air data (SODARS, a radar wind profiler, and (SODARS, a radar wind profiler, and radiosondes). They paid someone else for radiosondes). They paid someone else for analysis of ozone patterns, but we did some analysis of ozone patterns, but we did some analysis anyway because we were interested. analysis anyway because we were interested. So we were not as thorough as we would have So we were not as thorough as we would have been had we gotten paid to do the data analysis.been had we gotten paid to do the data analysis.
2005
Danger if you are downwind of California! (or Vegas or Phoenix)
Annual number of exceedances
Annual number of exceedances
4th highest O3
Typical summer California wind flow pattern- combination of sea-breeze and mountain-valley wind circulations
Frequency of Tehachapi Pass tracer Frequency of Tehachapi Pass tracer above background (July 12- Aug 31 above background (July 12- Aug 31
1992)1992)
High frequency of flow from O3 rich San Joaquin Valley to the SE, then NE
Frequency of El Centro tracer above Frequency of El Centro tracer above background (July 12 – Aug 31 1992)background (July 12 – Aug 31 1992)
Convergence zone transports emissions from Mexicali through LA Basin and San Joaquin Valley to the north and east
8 days (all in June and July) with one or more 8 days (all in June and July) with one or more long-term Clark County sites greater than 8 long-term Clark County sites greater than 8
hour standard of 85 ppb Ohour standard of 85 ppb O33 (May and June had (May and June had high frequency of troughs passing through)high frequency of troughs passing through)
40
60
80
100
120
140
160
4/30 5/10 5/20 5/30 6/9 6/19 6/29 7/9 7/19 7/29 8/8 8/18 8/28
Da
ily m
ax
8 h
r O
3 (
pp
b)
SJV max
SC max
CC max
Nearly every day South Coast maximum > San Joaquin Valley maximum > Clark County maximum
High regional ozone 500 mb chartHigh regional ozone 500 mb chart
Low regional ozone 500 mb chartLow regional ozone 500 mb chart
Summer 2005Summer 2005 daily 8-hour maximums- daily 8-hour maximums- Clark County, Jean, California Mohave Clark County, Jean, California Mohave
Desert Desert
40
50
60
70
80
90
100
110
120
130
4/30 5/10 5/20 5/30 6/9 6/19 6/29 7/9 7/19 7/29 8/8 8/18 8/28
Da
ily m
ax
8 h
r O
3 (
pp
b)
CC max
Jean
Mojave max
California Mojave Desert maximum typically considerably higher than Clark County maximum- provides high background
Summer 2005Summer 2005 daily 8-hour maximums- daily 8-hour maximums- Jean and Clark County maximumsJean and Clark County maximums
40
50
60
70
80
90
100
110
4/30 5/10 5/20 5/30 6/9 6/19 6/29 7/9 7/19 7/29 8/8 8/18 8/28
Da
ily m
ax
8 h
r O
3 (
pp
b)
CC max
Jean
Clark County maximum and Jean track well- bigger offset in July to early August than May-June; more local impact?
Summer 2005Summer 2005 daily 8-hour maximums- daily 8-hour maximums- San Joaquin Valley, Mojave Desert, San Joaquin Valley, Mojave Desert,
Palm SpringsPalm Springs
40
50
60
70
80
90
100
110
120
130
4/30 5/10 5/20 5/30 6/9 6/19 6/29 7/9 7/19 7/29 8/8 8/18 8/28
Da
ily m
ax
8 h
r O
3 (
pp
b)
SJV max
Mojave max
Palm Springs
Climatology of California ozone patterns- August SJV max> Mohave max>Palm Springs, max shifts northward?
Used cluster analysis of wind field patterns to form groups of days with similar surface winds
For each cluster of days, used cluster analysis to group hours with similar wind patterns
Generated resultant winds and average ozone concentrations for each site for each daily cluster for each group of hours
Used difference in ozone concentration from upwind to downwind of Las Vegas to estimate local versus regional transport contributions
Generated and plotted HYSPLIT backtrajectories for each cluster
Monitoring sites used in cluster analysis
Percentage of days in each cluster, by month; total number of days per cluster
Dates
Strong SW flow
Light northerly
flowSJV+LV
increment
Local terrain forced flow others
May 15-31 29 6 6 47 12
June 43 3 0 37 17
July 13 6 35 35 3
Aug 16 3 13 55 13
Total days per cluster 27 5 16 47 14
Climatology of transport patterns helps build conceptual model- Local terrain forced flow common all summer; strong SW early summer, SJV+LV increment July peak
Nighttime downslope flow for terrain forced cluster
By 7-10 am heating of east facing Spring Mtns causes upslope flows
Late morning to afternoon, valley flow develops, transporting urban precursors to the northwest and O3 is high there.
About 9 ppb local enhancement
Synoptic flows weak, HYSPLIT backtrajectories from all over, not real helpful
San Joaquin Valley + Las Vegas has light SW transport overnight, elevated O3 at high elevation sites
SJV + LV high O3 most of monitoring area, high background at Jean + local enhancement of about 9 ppb
Backtrajectories for SJV + LV show flow from SF Bay area through San Joaquin Valley, over Tehachapi pass and then into Las Vegas in convergence zone
Strong SW flow shows high background O3
Afternoon shows highest ozone at background site – 1 exceedance day at Jean
Backtrajectories for strong SW flow show about equal frequency from SJV and South Coast
ClusterRegional
Winds
Midday surface winds
Trajectory pathways Ozone levels
Las Vegas ozone
increment
Strong SW SW SW SJV, South Coast
Highest at background
sites – 1 exceedance
None apparent
Light N N N N Highest at Boulder City –
No exceedances
11 ppb
SJV + LV WSW SE SJV Highest NW LV Valley –
3 exceedances
8 ppb
Local Terrain Forced
Varied SE Varied Highest in NW LV Valley
– 4 exceedances
(2 fire days)
9ppb
Pattern summary table
178-544 m AGL
590-1047 m AGL
1183-3711 m AGL
9-11 am 3-6 pm 7-10 pm
Much vertical change in wind direction in morning, becomes SW all levels afternoon
SummarySummary Consideration of regional and local (and global?) Consideration of regional and local (and global?)
transport important in understanding causes of transport important in understanding causes of high ozonehigh ozone
Spatial pattern analysis, Cluster analysis and Spatial pattern analysis, Cluster analysis and backtrajectory analysis among the methods helpful backtrajectory analysis among the methods helpful in developing conceptual modelsin developing conceptual models
Far too few rural monitoring sites of OFar too few rural monitoring sites of O33 and and precursors in the western US to understand extent precursors in the western US to understand extent and cause of high ozone in the WRAP regionand cause of high ozone in the WRAP region
Need coordinated monitoring, modeling, and data Need coordinated monitoring, modeling, and data analysis effort over a large regionanalysis effort over a large region
Use modeling, EI’s, and analysis of existing data to Use modeling, EI’s, and analysis of existing data to design monitoring networksdesign monitoring networks