Precursor reductions and ground-level ozone in the Continental United States

Abstract

Numerous papers analyze ground-level ozone (O 3 ) trends since the 1980s, but few have linked O 3 trends with observed changes in nitrogen oxide (NO x ) and volatile organic compound (VOC) emissions and ambient concentrations. This analysis of emissions and ambient measurements examines this linkage across the United States on multiple spatial scales from continental to urban. O 3 concentrations follow the general decreases in both NO x and VOC emissions and ambient concentrations of precursors (nitrogen dioxide, NO 2 ; nonmethane organic compounds, NMOCs). Annual fourth-highest daily peak 8-hr average ozone and annual average or 98th percentile daily maximum hourly NO 2 concentrations show a statistically significant (p < 0.05) linear fit whose slope is less than 1:1 and intercept is in the 30 to >50 ppbv range. This empirical relationship is consistent with current understanding of O 3 photochemistry. The linear O 3 -NO 2 relationships found from our multispatial scale analysis can be used to extrapolate the rate of change of O 3 with projected NO x emission reductions, which suggests that future declines in annual fourth-highest daily average 8-hr maximum O 3 concentrations are unlikely to reach 65 ppbv or lower everywhere in the next decade. Measurements do not indicate increased annual reduction rates in (high) O 3 concentrations beyond the multidecadal precursor proportionality, since aggressive measures for NO x and VOC reduction are in place and have not produced an accelerated O 3 reduction rate beyond that prior to the mid-2000s. Empirically estimated changes in O 3 with emissions suggest that O 3 is less sensitive to precursor reductions than is found by the CAMx (v. 6.1) photochemical model. Options for increasing the rate of O 3 change are limited by photochemical factors, including the increase in NO x sensitivity with time (NMOC/NO x ratio increase), increase in O 3 production efficiency at lower NO x concentrations (higher O 3 /NO y ratio), and the presence of natural NO x and NMOC precursors and background O 3 .Implications: This analysis demonstrates empirical relations between O 3 and precursors based on long term trends in U.S. locations. The results indicate that ground-level O 3 concentrations have responded predictably to reductions in VOC and NO x since the 1980s. The analysis reveals linear relations between the highest O 3 and NO 2 concentrations. Extrapolation of the historic trends to the future with expected continued precursor reductions suggest that achieving the 2014 proposed reduction in the U.S. National Ambient Air Quality Standard to a level between 65 and 70 ppbv is unlikely within the next decade. Comparison of measurements with national results from a regulatory photochemical model, CAMx, v. 6.1, suggests that model predictions are more sensitive to emissions changes than the observations would support.

Ozone Response to Emission Reductions in the Southeastern United States

“…In one case, OPE has not changed over time in southern California, but changes in the relative proportions of NOx-oxidation products have occurred and are thought to be instrumental in driving the rapid rates of O3 decline in that area (Pollack et al, 2013 (Hidy and Blanchard, 2015). Proportionalities between O3 and NO2 that are less than 1:1 are expected, and the observed intercept terms are approximately consistent with typical O3 mixing ratios of ~20 -50 ppbv observed at remote monitoring sites (Oltmans et al, 2008;2013;U.S.…”

“…John et al, 1998;Sillman et al, 1998;Zaveri et al, 2003;Griffin et al, 2004;Travis et al, 2016). Long-term, post1990s data are widely available for O3 and NO2 but detailed observations of total oxidized nitrogen (NOy) and VOC, and 30 especially their component species, are typically lacking (e.g., Hidy and Blanchard, 2015). One of the longest records of urban and suburban data, comprising a series of short-term campaigns as well as continuous measurements, is from southern California.…”

“…The nature and magnitude of background O3 remain an active area of research in the U.S. and Europe (Naja et al, 2003;Solberg et al, 2005;Ordóñez et al, 2007;Cristofanelli and Bonasoni, 2009;Arif and Abdullah, 2011;Zhang et al, 2011;Wilson et al, 2012). Hidy and Blanchard (2015) discuss definitions of continental and regional background O3. For this study, we adopt a definition of "background" that includes both the non-anthropogenic component and the eastern 25 regional component.…”

Decadal changes in summertime reactive oxidized nitrogen and surface ozone over the Southeast United States

“…Satellite-and ground-based observations imply significant declines in US NO x emissions, with a decreasing rate of roughly −4 % yr −1 after 2005 (Krotkov et al, 2016;Russell et al, 2012;Tong et al, 2015;Miyazaki et al, 2017;Lu et al, 2015;Lamsal et al, 2015). This has proven effective at lowering near-surface ozone (O 3 ) in the past few decades (Cooper et al, 2012;Simon et al, 2015;Hidy and Blanchard, 2015;Stoeckenius et al, 2015;Xing et al, 2015;Yahya et al, 2016;Astitha et al, 2017). The average of the annual fourth highest daily maximum 8 h average (MDA8) ozone over 206 sites has decreased by 31 % from 101 ppb in 1980 to 70 ppb in 2016 across the continental US, with more significant reductions in rural areas of the eastern US in summer (Simon et al, 2015;Cooper et al, 2012).…”

Ozone troposphérique en France : distribution spatiale et tendances sur la période 1999-2012

“…Le transport transcontinental peut élever les concentrations en O 3 mesurées dans les stations françaises (Derwent et al, 2010) ) sur la période 1990-2010 (Hidy et Blanchard, 2015 ;Xing et al, 2015). (Godowitch et al, 2008).…”