An Assessment of Ground Level and Free Tropospheric Ozone Over California and Nevada

Abstract

Increasing free tropospheric ozone (O3), combined with the high elevation and often deep boundary layers at western U.S. surface stations, poses challenges in attaining the more stringent 70 ppb O3 National Ambient Air Quality Standard. As such, use of observational data to identify sources and mechanisms that contribute to surface O3 is increasingly important. This work analyzes surface and vertical O3 observations over California and Nevada from 1995 to 2015. Over this period, the number of high O3 events (95th percentile) at the U.S. Environmental Protection Agency Clean Air Status and Trends Network (CASTNET) sites has decreased during summer, as a result of decreasing U.S. emissions. In contrast, an increase in springtime 5th percentile O3 indicates a general increase of baseline O3. During 2012 there was a peak in exceedances and in the average spring‐summer O3 mixing ratios at CASTNET sites. Goddard Earth Observing System‐Chem results show that the surface O3 attributable to transport from the upper troposphere and stratosphere was increased in 2013 compared to 2012, highlighting the importance of measurements aloft. Vertical O3 measurements from aircraft, ozonesondes, and lidar show distinct seasonal trends, with a high percentage of elevated O3 laminae (O3 > 70 ppb, 3–8 km) during spring and summer. Analysis of the timing of high O3 surface events and correlation between surface and vertical O3 data is used to discuss varying sources of western U.S. surface O3.

Cabin air quality on non‐smoking commercial flights: A review of published data on airborne pollutants

“…Commercial aircraft typically cruise at an altitude of 18,000–41,000 feet (5490–12,500 meters) 63,120,121 . At these cruising altitudes, they are in the troposphere in higher latitudes 75 , where O 3 is at concentrations ranging from 25 ppb to ~900 ppb 75,122,123 . After entering the cabin, O 3 will decompose on surfaces and may also undergo reactions with other pollutants on surfaces and in the air; the resulting concentration will therefore be lower than in the supply air.…”

“…Commercial aircraft typically cruise at an altitude of 18,000-41,000 feet (5490-12,500 meters) 63,121,122 . At these cruising altitudes, they are in the troposphere in higher latitudes 75 , where O 3 is at concentrations ranging from 25 ppb to ~900 ppb 75,123,124 .…”

The California Baseline Ozone Transport Study (CABOTS)

“…Numerous modeling (Jacob et al 1999;Lin et al 2012b;Pfister et al 2011) and measurement (Cooper et al 2011;Jaffe et al 1999;Parrish et al 2014;Yates et al 2017) studies have examined the impact of baseline ozone on surface concentrations across California, but there remains a great deal of uncertainty about the contributions of stratospheric and other transported ozone to surface concentrations in the San Joaquin Valley (SJV), the southern part of the California Central Valley and one of only two "extreme" ozone nonattainment areas remaining in the United States (U.S. EPA Green Book, www.epa.gov/green-book). Much of this uncertainty is thought to result from a lack of detailed information about the vertical distribution of ozone.…”

Diverging Ozone Trends Above Western North America: Boundary Layer Decreases Versus Free Tropospheric Increases

“…The data sets are as follows: (a) ozonesondes launched at Boulder (Colorado, 1967–2021), Trinidad Head (THD, California, 1997–2021), Edmonton (Canada, 1970–2021), Kelowna (Canada, 2003–2017) and Port Hardy (Canada, 2018–2021), with a sampling frequency of approximately once per week (Sterling et al., 2018; Tarasick et al., 2016); (b) The lidar operated at the Jet Propulsion Laboratory Table Mountain Facility (TMF, California) has typically measured 2–5 profiles per week since 1999 (McDermid et al., 2002), with an increased frequency in the most recent years (Chouza et al., 2019); (c) The IAGOS program has measured ozone from multiple commercial aircraft since 1994 (Blot et al., 2021; Nédélec et al., 2015; Petzold et al., 2015). Ozone profiles above WNA mainly occurred above the international airports at Vancouver, San Francisco, Portland, and Los Angeles; a limitation of the IAGOS data set is the occurrence of many intermittent data gaps over this region (see Figure 1 for the annual sample size); and (d) the NASA AJAX field campaign data set includes 199 flights during 2011–2018 (Iraci et al., 2021; Yates et al., 2016, 2017), and the SNAAX (Scientific Aviation NASA Ames Airborne eXperiment) data set includes 10 flights during 2018–2019. While most of these data sets were previously used in the recent study by Chang et al.…”