Emission influences on air pollutant concentrations in New York State: I. ozone

Abstract

Abstract Relationships between regional air pollutant emissions and ambient concentration trends in New York State are studied. Large (∼50–85%) reductions in anthropogenic emissions occurred in the northeastern U.S. and eastern Canada between 1995 and 2015. Spatially and temporally aggregated ambient concentrations of O3 precursors declined steadily along with emission reductions: multi-site mean annual nitrogen dioxide (NO2), carbon monoxide (CO), and toluene concentrations tracked state and regional emissions of oxides of nitrogen (NOx, NO + NO2), CO, and volatile organic compounds (VOC), respectively (r2 = 0.97, 0.88, and 0.73), showing linear responses of average O3 precursor concentrations to both state and regional emission reductions. O3 exhibited complex spatial and temporal variations, indicating that O3 was influenced not only by the steady decline of regional emissions but also by subregional emission changes, chemical and physical processes, and day-specific variations in emissions and weather. The statewide multi-site mean annual 4th-highest daily 8-h O3 peak declined at the rate of 0.86 ± 0.14 ppbv y−1 (1.1% y−1). Influences on peak daily 8-h O3 were studied using a long-term data record from a research site at Pinnacle State Park (PSP), located near Addison, New York. A generalized additive model (GAM) was applied to separate the influences of local and regional emission changes, weather, and other factors. GAM results indicate that the reduction of summer O3 peak values and the overall trends in O3 at PSP were due to changes in ambient pollutant levels, rather than to trends in temperature or other meteorological factors. Whereas PSP summer O3 was NOx-sensitive, O3 was often VOC-sensitive during winter and spring days. The frequency of VOC-sensitive days decreased between 2001 – 2005 and 2012–2016, consistent with an expectation of increasing NOx sensitivity as ambient NOx concentrations decline.