Person:

Jhun, Iny

Air quality is heavily influenced by weather conditions. In this study, we assessed the impact of long-term weather changes on air quality and health in the US during 1994–2012. We quantified past weather-related increases, or ‘weather penalty’, in ozone (O3) and fine particulate matter (PM2.5), and thereafter estimated the associated excess deaths. Using statistical regression methods, we derived the weather penalty as the additional increases in air pollution relative to trends assuming constant weather conditions (i.e., weather-adjusted trends). During our study period, temperature increased and wind speed decreased in most US regions. Nationally, weather-related 8 h max O3 increases were 0.18 ppb per year (95% CI: 0.06, 0.31) in the warm season (May–October) and 0.07 ppb per year (95% CI: 0.02, 0.13) in the cold season (November–April). The weather penalties on O3 were relatively larger than PM2.5 weather penalties, which were 0.056 µg m−3 per year (95% CI: 0.016, 0.096) in warm months and 0.027 µg m−3 per year (95% CI: 0.010, 0.043) in cold months. Weather penalties on O3 and PM2.5 were associated with 290 (95% CI: 80, 510) and 770 (95% CI: 190, 1350) excess annual deaths, respectively. Over a 19-year period, this amounts to 20 300 excess deaths (5600 from O3, 14 700 from PM2.5) attributable to the weather penalty on air quality

Ozone (O-3) has harmful effects on human health and ecosystems. In the USA, significant reductions of O-3 precursors-nitrogen oxides (NOx) and volatile organic compounds (VOCs)-have not yielded proportionate decreases in O-3. NOx is a major precursor of O-3 as well as a quencher of O-3 through NOx titration, which is especially important during the night and wintertime. In this study, we investigated the potential dual impact of NOx concentration decreases on recent O-3 trends by season and time of day. We analyzed hourly O-3 and NOx measurement data between 1994 and 2010 in the continental USA. Nationally, hourly O-3 concentrations decreased by as much as -0.38 ppb/year with a standard error of 0.05 ppb/year during the warm season midday, but increased by as much as +0.30 +/- 0.04 ppb/year during the cold season. High O-3 concentrations (>= 75th percentile) during the warm season decreased significantly, however, there were notable increases in the cold season as well as warm season nighttime; we found that these increases were largely attributable to NOx decreases as less O-3 is quenched. These O-3 increases, or "penalties", related to NOx reductions remained robust at a wide range of O-3 concentrations (5th to 99th percentile), and even after accounting for VOC reductions and meteorological parameters, including temperature, wind speed, and water vapor pressure. In addition, we observed O-3 penalties across rural, suburban, and urban areas. Nonetheless, peak O-3 concentrations (99.9th percentile) were mitigated by NOx reductions. In addition, there was some suggestive evidence that VOC reductions have been more effective in reducing O-3.