The California Baseline Ozone Transport Study (CABOTS)

Abstract

Ozone is one of the six “criteria” pollutants identified by the U.S. Clean Air Act Amendment of 1970 as particularly harmful to human health. Concentrations have decreased markedly across the United States over the past 50 years in response to regulatory efforts, but continuing research on its deleterious effects have spurred further reductions in the legal threshold. The South Coast and San Joaquin Valley Air Basins of California remain the only two “extreme” ozone nonattainment areas in the United States. Further reductions of ozone in the West are complicated by significant background concentrations whose relative importance increases as domestic anthropogenic contributions decline and the national standards continue to be lowered. These background concentrations derive largely from uncontrollable sources including stratospheric intrusions, wildfires, and intercontinental transport. Taken together the exogenous sources complicate regulatory strategies and necessitate a much more precise understanding of the timing and magnitude of their contributions to regional air pollution. The California Baseline Ozone Transport Study was a field campaign coordinated across Northern and Central California during spring and summer 2016 aimed at observing daily variations in the ozone columns crossing the North American coastline, as well as the modification of the ozone layering downwind across the mountainous topography of California to better understand the impacts of background ozone on surface air quality in complex terrain.

The Status of Air Quality in the United States During the COVID-19 Pandemic: A Remote Sensing Perspective

“…Also, no reduction could be seen in the 1 • IAV time series plots over San Francisco and Los Angeles (Figure 5). The US west coast frequently experiences long-range trans-pacific transport events from Asia and Europe that result in increased pollutants' levels in this region [55,72], which also peaks in late spring, coinciding with the pandemic lockdown incidence. The increase or no change in NO 2 levels in San Francisco despite reduced NO 2 emissions from their large traffic volume demonstrates that other sources dominate, e.g., meteorology and pollution events [14,73].…”

The Fires, Asian, and Stratospheric Transport-Las Vegas Ozone Study (FAST-LVOS)

“…Planning for the FAST-LVOS day-to-day activities and IOPs relied primarily on long range weather forecasts from the (Stein et al, 2015), and stratospheric, Asian pollution, and biomass burning tracers calculated using the FLEXPART particle dispersion model (Brioude et al, 2009;Brioude et al, 2007). The RAP-Chem and FLEXPART models were also used to support the 2016 CABOTS field campaign and are described elsewhere (Faloona et al, 2020). The FAST-LVOS measurements were also simulated by the GEOS-Chem and NOAA Geophysical Fluid Dynamics Laboratory (NOAA GFDL) AM4 chemistry-climate models; these efforts are described in the companion paper by Zhang et al ((Zhang et al, 2020).…”

“…Previous airborne and ground-based lidar measurements have shown that elevated O3 layers are common features of the lower free troposphere between ~3 and 6 km a.s.l. above California (Langford et al, 2012;Ryerson et al, 2013;Faloona et al, 2020) and southern Nevada (Langford et al, 2015b;Langford et al, 2017) in late spring and early summer, and it is well established that the U.S. West Coast is one of the global hotspots for deep stratosphere-to-troposphere transport (STT) of O3 in springtime (Wernli and Bourqui, 2002;Sprenger and Wernli, 2003;James et al, 2003;Skerlak et al, 2014;Skerlak et al, 2015;Breeden et al, 2021). Deep STT refers to those intrusions that descend from the tropopause to 700 hPa in 5 days or less (Wernli and Bourqui, 2002;Sprenger and Wernli, 2003), and occurs primarily through the formation of tropopause folds, tongues of lower stratospheric air that descend isentropically beneath the jet stream circulating around upper-level lows.…”

Ozone Production in the Soberanes Smoke Haze: Implications for Air Quality in the San Joaquin Valley During the California Baseline Ozone Transport Study

“…The CABOTS field campaign (Faloona et al, 2020) was organized by the California Air Resources Board to investigate the contributions of background O 3 originating from Asian pollution (Lin, Fiore, Horowitz et al, 2012) and stratospheric intrusions (Lin, Fiore, Cooper et al, 2012) on surface concentrations in the SJVAB (Figure 1). The study was conducted between late May and mid‐August of 2016 with two intensive operating periods (IOP1: 27 May to 18 June and IOP2: 18 July to 7 August).…”

“…In this paper, we use airborne, surface, and remote sensing measurements made during the 2016 California Baseline Ozone Transport Study (CABOTS) (Faloona et al, 2020) to examine the production of O 3 in the Soberanes Fire plume and estimate the impact on surface O 3 concentrations in the SJVAB during the summer of 2016. This fire, which burned more than 52,600 ha (130,000 acres) along the central California coast between 22 July and 12 October 2016, created an elevated smoke haze that covered the southern and central SJVAB in late July and early August.…”