Impact of Transported Background Ozone on Western U.S. Air Quality David Parrish CIRES University of Colorado NOAA/ESRL Chemical Sciences Division Boulder, Colorado USA Consultant with David.D.Parrish, LLC (Background Ozone = that transported into U.S. = Baseline Ozone)

Impact of Transported Background Ozone on Western U.S. Air Quality Today: Overview of trends in U.S. O 3 concentrations Historical trends of O 3 in California’s air basins Results from Las Vegas Ozone Study

Impact of Transported Background Ozone on Western U.S. Air Quality Acknowledgements: Many people have provided O 3 data sets (CARB) 2 modeling studies: Meiyun Lin – Princeton/ NOAA/GFDL Jerome Brioude - CIRES/ NOAA ESRL CSD

Overview of trends in U.S. O 3 concentrations Owen R. Cooper CIRES/NOAA ESRL CSD Trends ( ) in ozone design values*. Emission reductions have been remarkably effective throughout most of U.S. Mean eastern US trend: -1.3 ± 0.6 ppb yr-1 (1 standard deviation). significant increase insignificant increase significant decrease insignificant decrease ppb/yr Mean trend: -1.3 ppb/yr (Taken from * Ozone design value = 3 year running mean of annual 4 th highest maximum 8 hr average ozone.

Overview of trends in U.S. O 3 concentrations Owen R. Cooper CIRES/NOAA ESRL CSD Trends ( ) in ozone design values. Emission reductions have been remarkably effective throughout most of U.S. Mean eastern US trend: -1.3 ± 0.6 ppb yr-1 (1 standard deviation). Mean western US trends: -1.0 ± 0.6 ppb yr-1all -0.6 ± 0.7 ppb yr-1 > 1km -0.4 ± 0.7 ppb yr-1 rural & > 1km significant increase insignificant increase significant decrease insignificant decrease Mean trend: -1.3 ppb/yr (Taken from

Overview of trends in U.S. O 3 concentrations Owen R. Cooper CIRES/NOAA ESRL CSD Compare 5 high altitude rural sites Whiteface Mtn m Big Meadows 1073 m Cove Mtn m Mt. Bachelor 2763 m Lassen NP 1756 m April - May

Overview of trends in U.S. O 3 concentrations Owen R. Cooper CIRES/NOAA ESRL CSD Compare 5 high altitude rural sites Ozone (ppb) Small symbols, dashed lines = 95%ile Large symbols, solid lines = median Whiteface Mtn. Big Meadows Cove Mtn. April - May

Overview of trends in U.S. O 3 concentrations Owen R. Cooper CIRES/NOAA ESRL CSD Compare 5 high altitude rural sites Ozone (ppb) Small symbols, dashed lines = 95%ile Large symbols, solid lines = median Whiteface Mtn. Big Meadows Cove Mtn. Lassen NP April - May

Overview of trends in U.S. O 3 concentrations Owen R. Cooper CIRES/NOAA ESRL CSD Compare 5 high altitude rural sites Ozone (ppb) Small symbols, dashed lines = 95%ile Large symbols, solid lines = median Mt. Bachelor Whiteface Mtn. Big Meadows Cove Mtn. Lassen NP April - May

Overview of trends in U.S. O 3 concentrations Owen R. Cooper CIRES/NOAA ESRL CSD Compare 5 high altitude rural sites Ozone (ppb) Small symbols, dashed lines = 95%ile Large symbols, solid lines = median Mt. Bachelor Whiteface Mtn. Big Meadows Cove Mtn. Lassen NP Aircraft – Western North America free troposphere U.S. median trends (April - May): East: ppb/yr West: ppb/yr April - May

Overview of trends in U.S. O 3 concentrations Owen R. Cooper CIRES/NOAA ESRL CSD Sites: Glacier, Yellowstone, Pinedale, Centennial, RMNP, Gothic, G. Canyon, Chiricahua, Sequoia, Lassen, Great Basin, Yosemite, Mesa Verde, Canyonlands, Walden, Petrified Forest, Escalante, Zion, Dinosaur, Joshua Tree- Black Rock, Joshua Tree-Cottonwood Canyon, Meeker, Craters of the Moon, Grand Teton Ozone design values - high altitude rural sites ≥ 76 ppb ppb ppb ppb ≤ 60 ppb 8 of 24 sites currently exceed 70 ppb NAAQS

Historical trends of O 3 in California’s air basins * How has O 3 evolved in response to emission controls in these different air basins? O 3 has been measured in nearly all 15 since coastal, 2 in Central Valley, deserts, mountains, etc. South Coast has one of the most populous urban areas in the U.S. Geology and land-use spectrum gives a wide spectrum of ozone precursor emission sources.

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0  = response time of emission controls South Coast Historical trends of O 3 in California’s air basins

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : South Coast Historical trends of O 3 in California’s air basins y 0 = 56 ppb A = 180 ppb  = 22 years y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0  = response time of emission controls

South Coast Historical trends of O 3 in California’s air basins y 0 = 56 ppb 39 ppb A = 180 ppb  = 22 years During the highest 10% of O 3 episodes: In 1980 local contribution (180 ppb) > 3X baseline contribution In 2014 local contribution (39 ppb) only ~70% of baseline contribution Large O 3 reductions have been accomplished, but not much more is possible (90 th percentile approximates design value)

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls South Coast Historical trends of O 3 in California’s air basins Each curve has its own y 0 value: maximum = 68 ± 14 ppb 90th percentile = 56 ± 6 ppb median = 50 ± 6 ppb 25th percentile = 49 ± 7 ppb  = 22 years Each curve also has its own A value, but a common response time: 22 years  = 22 years is 15 year half-life y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0

San Diego:  = 22 years Examine Baseline O 3 in other air basins y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0  = response time of emission controls 90th percentile, South Coast: A = 180 ppb y 0 = 56 ± 6 ppb 90th percentile, San Diego: A = 68 ppb y 0 = 58 ± 4 ppb Historical trends of O 3 in California’s air basins

y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0  = response time of emission controls North Coast: linear fit 90th percentile, South Coast: A = 180 ppb y 0 = 56 ± 6 ppb 90th percentile, San Diego: A = 68 ppb y 0 = 58 ± 4 ppb 90th percentile, North Coast: y 2000 = 51 ± 3 ppb O 3 coming ashore at sea level along the coast of California is 50 – 60 ppb or higher on 10% of days during ozone season. Historical trends of O 3 in California’s air basins Examine Baseline O 3 in other air basins

South Coast Historical trends of O 3 in California’s air basins  = 22 years 90th %ile, South Coast: A = 180 ppb y 0 = 56 ± 6 ppb y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 Examine Baseline O 3 in other air basins

Mojave Desert Historical trends of O 3 in California’s air basins  = 22 years 90th %ile, South Coast: A = 180 ppb y 0 = 56 ± 6 ppb 90th %ile, Mojave Desert: A = 80 ppb y 0 = 74 ± 11 ppb y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 O 3 transported into Mojave Desert from outside the U.S. is > 74 ± 11 ppb on 10% of days during ozone season. Examine Baseline O 3 in other air basins

South Coast AB median and 25 th %ile are now lower than in the Mojave Desert On most days of ozone season, max 8hr O 3 higher in Mojave Desert AB than SoCAB Historical trends of O 3 in California’s air basins Compare two basins

Historical trends of O 3 in California’s air basins Project into future If same trends continue, Mojave Desert AB will soon have higher 90 th %ile than SoCAB. More difficult for Mojave Desert AB to reach new NAAQS than SoCAB. South Coast AB median and 25 th %ile are now lower than in the Mojave Desert On most days of ozone season, max 8hr O 3 higher in Mojave Desert AB than SoCAB

Sponsored by the Clark County Department of Air Quality Andrew O. Langford CIRES/NOAA ESRL CSD Goal: Study Impact of stratospheric intrusions and long-range transport on surface air quality

* Clark County exceedance days ** * Ozone (ppb) Powerhouse Fire

* Clark County exceedance days Powerhouse Fire Las Vegas CO (ppb) ** * Exceedance day with low CO

* Clark County exceedance days ** * Ozone (ppb) Powerhouse Fire Low CO means O 3 not from urban areas or wild fires

High O 3 layers (STT) ppb ** Altitude (m AGL) Altitude (m ASL) * Clark County exceedance days

First measurements following a stratospheric intrusion down to the surface! Ozone (ppb) CO (ppb) High O 3 = low CO, dry air

Surface O 3 anticorrelated with H 2 O and CO : O 3 of stratospheric origin O3- Ozone (ppb) CO (ppb)

May 21 May 25 Ozone (ppb) Angel Peak (NOAA) Jean NV (Clark Co.) Great Basin NP (NPS) Stratospheric air observed at Angel Peak had region-wide influence. Las Vegas Jean NV Great Basin NP

Stratospheric air at start of each exceedance day. Asian pollution also contributed to first exceedance. No significant wildfire contributions to 3 exceedance days. Jerome Brioude (NOAA/CIRES)

Meiyun Lin (NOAA/GFDL/Princeton) Stratospheric contribution to MDA8: ppbv in May-June 2013 Observed AM3 total AM3 stratosphere Las Vegas Jean NV nnn Asian contribution to MDA8: 5-15 ppb Total background: typically ppb U.S. contribution usually quite small! ?

> 30% exceedance rate for 70 ppb NAAQS in this period Baseline O 3 is increasing during this season Maximum Average Angel Peak

70 ppb May-June Jean NV Crestline SoCAB Day of year Max Daily 8-hr O 3 At higher elevations in the western U.S., O 3 from the stratosphere is very important – maximizes in spring As anthropogenic O 3 is further reduced, maximum O 3 concentrations will occur earlier in year. High O 3 in the rural west is not primarily due to transport from Los Angeles.

Impact of Transported Background Ozone on Western U.S. Air Quality Summary and Conclusions

Mean trend: -1.3 ppb/yr Mean trend/yr Mean trend: -1.3 ppb/yr Me an tren d: -1.3 pr Me an tren d: -1.3 Over the decades, emission reductions have been remarkably effective in reducing U.S. surface O 3 Processes controlling O 3 are now very different in eastern and western U.S.

In the western U.S., baseline ozone is a very large fraction of the total, and is increasing Finding T1: Transport of baseline O 3 can enhance surface O 3 concentrations to such an extent that the margin for local and regional O 3 production before exceeding the NAAQS is greatly reduced or potentially eliminated, even in California's urban areas. Finding T2: Transport of baseline ozone accounts for a majority of surface ozone concentrations in California at urban as well as rural locations, both on average and during many exceedance events. Only in the most intense exceedance events does local and regional photochemical production contribute the majority.

In California, high O 3 has become a rural, even more than an urban, issue (even more so in the San Joaquin Valley).

Impact of Transported Background Ozone on Western U.S. Air Quality Thank you for your attention!

Mojave Desert Historical trends of O 3 in California’s air basins  = 22 years Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls Each curve has its own y 0 value: maximum = 75 ± 20 ppb 90th percentile = 74 ± 11 ppb median = 67 ± 6 ppb 25th percentile = 64 ± 4 ppb Each curve also has its own A value, but a common response time: 22 years

Mojave Desert Historical trends of O 3 in California’s air basins  = 22 years Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls Each curve has its own y 0 value: maximum = 75 ± 20 ppb 90th percentile = 74 ± 11 ppb median = 67 ± 6 ppb 25th percentile = 64 ± 4 ppb Each curve also has its own A value, but a common response time: 22 years National Design Value

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls San Joaquin Valley Historical trends of O 3 in California’s air basins Each curve has its own y 0 value: maximum = 108 ± 7 ppb 90th percentile = 95 ± 5 ppb median = 82 ± 4 ppb 25th percentile = 73 ± 5 ppb  = 22 years Each curve also has its own A value, but a common response time: 22 years

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls Salton Sea Historical trends of O 3 in California’s air basins Each curve has its own y 0 value: maximum = 83 ± 13 ppb 90th percentile = 74 ± 3 ppb median = 66 ± 2 ppb 25th percentile = 61 ± 3 ppb  = 22 years Each curve also has its own A value, but a common response time: 22 years

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls South Central Coast Historical trends of O 3 in California’s air basins Each curve has its own y 0 value: maximum = 71 ± 8 ppb 90th percentile = 60 ± 5 ppb median = 53 ± 3 ppb 25th percentile = 50 ± 3 ppb  = 22 years Each curve also has its own A value, but a common response time: 22 years

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls San Francisco Bay Historical trends of O 3 in California’s air basins Each curve has its own y 0 value: maximum = 81 ± 10 ppb 90th percentile = 59 ± 5 ppb median = 44 ± 3 ppb 25th percentile = 39 ± 2 ppb  = 22 years Each curve also has its own A value, but a common response time: 22 years

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls Sacramento Valley Historical trends of O 3 in California’s air basins Each curve has its own y 0 value: maximum = 96 ± 9 ppb 90th percentile = 81 ± 5 ppb median = 66 ± 3 ppb 25th percentile = 57 ± 3 ppb  = 22 years Each curve also has its own A value, but a common response time: 22 years

Daily Maximum 8-hour average O 3 anywhere in basin May – September O 3 season Calculate maximum, 90 th %, 50 th and 25 th percentiles Plot time evolution Least-squares regression fit to : y 0 = baseline O 3 contribution A = 1980 O 3 enhancement above y 0 t = year; t 0 = 1980  = response time of emission controls Mountain Counties Historical trends of O 3 in California’s air basins Each curve has its own y 0 value: maximum = 98 ± 14 ppb 90th percentile = 82 ± 7 ppb median = 70 ± 5 ppb 25th percentile = 63 ± 5 ppb  = 22 years Each curve also has its own A value, but a common response time: 22 years