Photochemical Production of Ozone and Emissions of NO<sub>x</sub> and CH<sub>4</sub> in the San Joaquin Valley

Abstract

Midday summertime flight data collected in the atmospheric boundary layer (ABL) of California's San Joaquin Valley (SJV) are used to investigate the scalar budgets of NOx, O3, and CH4 in order to quantify the individual processes that control near surface concentrations yet are difficult to constrain from surface measurements alone: most importantly, 10 horizontal advection and entrainment mixing from above. The setting is a large mountain-valley system with a small aspect ratio where topography and persistent temperature inversions impose strong restraints on ABL ventilation. In conjunction with the observed time rate of change this airborne budgeting technique enables us to deduce net photochemical ozone production rates and emission fluxes of NOx and CH4. Measured NOx emissions from our principal flight domain were 216 (± 33) metric tons/ day averaged over six flights in July and August, which is nearly double the California government's 15 NOx inventory for the surrounding three county region. We consider several possibilities for this discrepancy including the influence of wildfires, the temporal bias of the airborne sampling, instrumental interferences, and the recent hypothesis presented by Almaraz et al. (2018) of localized high soil NO emissions from intensive agricultural application of nitrogen fertilizers in the region and find the latter to be the most likely explanation. The methane emission average was 438Gigagrams/ year (± 143), which exceeds an emissions inventory for the region by almost a factor of two as well. Measured 20 ABL ozone during the six afternoon flights averaged 74 ppb ( =9.8 ppb). The average mid-afternoon ozone rise of 2.8 ppb/h was found to be comprised of -0.8 ppb/h due to horizontal advection of lower O3 levels upwind, -2.2 ppb/h from dry deposition loss, -0.5 ppb/h from dilution by entrainment mixing, and 6.7 ppb/h net in-situ photochemical production. The O3 production rates exhibited a dependence on NO2 concentrations (r 2 = 0.35), and no discernible dependence on methane concentrations (r 2 ~ 0.02) which are correlated with many of the dominant VOC's in the region, suggesting that the ozone 25Atmos. Chem. Phys. Discuss., https://doi.

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

“…Visalia is located about one third of the way from Fresno to Bakersfield, the two most populous cities in the San Joaquin Valley (SJV), and the TOPAZ lidar was colocated with a radar wind profiler and Radio Acoustic Sounding System operated by the San Joaquin Valley Air Pollution Control District (Bao et al, 2008) and a vertically staring Doppler lidar operated by NOAA. Ozone, CO 2 , CH 4 , and other species were also sampled by single‐engine Mooney TLS Bravo and Ovation 2 research aircraft operated by the University of California, Davis (UC Davis) and Scientific Aviation (SciAv) (Trousdell et al, 2019) and by the NASA Alpha Jet Atmospheric eXperiment (AJAX) research aircraft (Yates et al, 2015). Details of the sampling techniques and intercomparisons between the lidar and airborne O 3 measurements are described in Leblanc et al (2018) and Langford et al (2019).…”

“…Widespread agricultural irrigation (Li et al, 2016) and subsidence created by the mountain‐valley circulations and persistent North Pacific High (Trousdell et al, 2016) typically cap the afternoon mixed layers below 1 km (Bianco et al, 2011), and some of the pollution carried into the mountains by the afternoon upslope winds (Panek et al, 2013) is recirculated back over the valley above the shallow boundary layers (De Young et al, 2005; Fast et al, 2012; Gohm et al, 2009; Rampanelli et al, 2004; Zardi & Whiteman, 2013). There, the pollution accumulates in a persistent “buffer layer” (Faloona et al, 2020; Trousdell et al, 2019) that can persist for days or even weeks until dispersed by passing cold frontal systems. During CABOTS, free tropospheric air flowing over the Coast Ranges also carried smoke from the Soberanes Fire into the buffer layer where it mingled with the anthropogenic pollution.…”

“…The TLS carried a 2B Technologies Model 205 O 3 monitor and a Picarro 2301f Cavity Ring‐Down Spectrometer to measure CO 2 , CH 4 , and H 2 O. The aircraft also carried an Eco Physics Model CLD 88 chemiluminescence detector with a photolytic converter for NO 2 , but these measurements were plagued by noise on some of the flights (Trousdell et al, 2019) and are not used here. The ad hoc EPA/Bay Area Air Quality Management District program consisted of morning (0800–1000 PDT) flights between Fresno and San José and afternoon (1200–1600 PDT) flights above the Fresno‐Visalia area.…”

Changes in the Relative Importance of Biogenic Isoprene and Soil NOx Emissions on Ozone Concentrations in Nonattainment Areas of the United States

“…With wide reductions in NOx emissions across the United States (Duncan et al., 2016; Hidy & Blanchard, 2015; Parrish et al., 2011), satellite‐ and ground‐based monitoring analyses demonstrate that O 3 production in urban areas of the country is transitioning from mostly VOC‐limited to increasingly NOx‐limited (Baidar et al., 2015; Blanchard & Hidy, 2018; He et al., 2019; Jin et al., 2017; Pusede & Cohen, 2012; Pusede et al., 2015). Recent observational evidence has subsequently supported the growing importance of soil NOx emissions on O 3 levels in some areas (Almaraz et al., 2018; Oikawa et al., 2015; Romer et al., 2018; Trousdell et al., 2019), but this work has been limited to short‐term field campaigns in specific regions (e.g., California and the Southeast United States), without attention on the potential impacts across all U.S. nonattainment areas.…”

“…. Recent observational evidence has subsequently supported the growing importance of soil NOx emissions on O 3 levels in some areas (Almaraz et al, 2018;Oikawa et al, 2015;Romer et al, 2018;Trousdell et al, 2019), but this work has been limited to short-term field campaigns in specific regions (e.g., California and the Southeast United States), without attention on the potential impacts across all U.S. nonattainment areas.…”