Mark Green and Dave DuBois Desert Research Institute

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)

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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

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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

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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

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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

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ax

8 h

r O

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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