On the observed response of ozone to NO<sub>x</sub> and VOC reactivity reductions in San Joaquin Valley California 1995–present

Abstract

Abstract. We describe the effects of nitrogen oxide (NO x ) and organic reactivity reductions on the frequency of high ozone days in California's San Joaquin Valley. We use sixteen years of observations of ozone, nitrogen oxides, and temperature at sites upwind, within, and downwind of three cities to assess the probability of exceeding the California 8-h average ozone standard of 70.4 ppb at each location. The comprehensive data records in the region and the steep decreases in emissions over the last decade are sufficient to constrain the relative import of NO x and organic reactivity reductions on the frequency of violations. We show that high ozone has a large component that is due to local production, as the probability of exceeding the state standard is lowest for each city at the upwind site, increases in the city center, is highest at downwind locations, and then decreases at the receptor city to the south. We see that reductions in organic reactivity have been very effective in the central and northern regions of the San Joaquin but less so in the southern portion of the Valley. We find evidence for two distinct categories of reactivity sources: one source that has decreased and dominates at moderate temperatures, and a second source that dominates at high temperatures, particularly in the southern San Joaquin, and has not changed over the last twelve years. We show that NO x reductions are already effective or are poised to become so in the southern and central Valley, where violations are most frequent, as conditions in these regions have or are transitioning to NO x -limited chemistry when temperatures are hottest and high ozone most probable.

On the temperature dependence of organic reactivity, nitrogen oxides, ozone production, and the impact of emission controls in San Joaquin Valley, California

“…We note that it has been previously speculated that a missing source of VOCR is important when O 3 is high in the SJV (Steiner et al, 2008;Hu et al, 2012;Pusede and Cohen, 2012). Organic sources with this temperature dependence include molecules with emission rates controlled by their vapor pressures, biogenic VOCs from forests The temperature-dependent VOCR is equal to the measured OH reactivity minus the temperature-independent i VOCR i and minus the OH reactivities of NO 2 , NO, HONO, HNO 3 , NH 3 , and SO 2 .…”

“…Skies were mostly cloudless during CalNex-SJV with the measured daily average photosynthetically active radiation (PAR) independent of temperature at daily maximum temperatures greater than 22 • C. Throughout this manuscript we define low, moderate, and high temperature regimes as follows: low -daily maximum temperatures of 17-27 • C (days between 1 May-31 October), moderate -daily maximum temperatures of 28-33 • C, and high -daily maximum temperatures of 34-45 • C. In 2010 there were 38 low temperature days, 54 moderate temperature days, and 80 high temperature days. These temperature cutoffs were selected in order to be consistent with Pusede and Cohen (2012). We also refer to the 2010 average low, moderate, and high temperatures, 24.7 • C, 30.8 • C, and 36.4 • C, which are averages of the 2010 1 h daily maximum temperature record and not of the 1 h daily maximum temperatures observed during the cooler, springtime CalNex-SJV study period.…”

“…In Pusede and Cohen (2012), we examined relationships between nitrogen oxides, the frequency of O 3 exceedances, and temperature, which we used as a proxy for VOCR, over the period 1996-2010, inferring from the observed nonlinear nitrogen oxide dependence that chemical production rather than meteorology dominated the statistics of violations in the San Joaquin Valley (SJV). We showed that in the northern SJV (Stockton plume) and central SJV (Fresno plume) P O 3 has largely been sensitive to VOCR and that organic emission reductions led to decreases in the frequency of O 3 violations.…”

Mechanism of the hydroxyl radical oxidation of methacryloyl peroxynitrate (MPAN) and its pathway toward secondary organic aerosol formation in the atmosphere

“…This NO x sensitivity translates to regional environmental impacts. For example, the high-NO x oxidation of isoprene controls the production of tropospheric ozone in regions rich with biogenic hydrocarbons [1][2][3] by accelerating the cycling of NO x and producing NO x reservoir species (e.g., organic nitrates and peroxynitrates). Isoprene chemistry also affects global climate primarily through the formation of secondary organic aerosol (SOA).…”

Observed trends in ground-level O<sub>3</sub> in Monterrey, Mexico, during 1993–2014: comparison with Mexico City and Guadalajara

“…Since the 1990s, reductions in O 3 precursor emissions in economically developed countries have resulted in decreases in tropospheric O 3 levels (Schultz and Rast, 2007;Butler et al, 2012;Pusede et al, 2012); however, in some regions, increases in O 3 have also been reported. For instance, from an analysis of O 3 data from 179 urban sites over France during 1999, Sicard et al (2016 reported an increasing trend in the annual averages of 0.14 ± 0.19 ppb yr −1 , and in the medians of 0.13 ± 0.22 ppb yr −1 , attributed to long-range transport and reduced O 3 titration by NO due to reductions in local NO x emissions.…”