Abstract. We investigated the ozone pollution trend and its sensitivity to keyprecursors from 1990 to 2015 in the United States using long-term EPA Air Quality System (AQS)observations and mesoscale simulations. The modeling system, a coupledregional climate–air quality model (CWRF-CMAQ; Climate-Weather Research Forecast andthe Community Multiscale Air Quality), captured well the summersurface ozone pollution during the past decades, having a mean slope oflinear regression with AQS observations of ∼0.75. While theAQS network has limited spatial coverage and measures only a few keychemical species, CWRF-CMAQ provides comprehensive simulations to enablea more rigorous study of the change in ozone pollution and chemicalsensitivity. Analysis of seasonal variations and diurnal cycle of ozoneobservations showed that peak ozone concentrations in the summer afternoondecreased ubiquitously across the United States, up to 0.5 ppbv yr−1 in majornon-attainment areas such as Los Angeles, while concentrations at certainhours such as the early morning and late afternoon increased slightly.Consistent with the AQS observations, CMAQ simulated a similar decreasingtrend of peak ozone concentrations in the afternoon, up to 0.4 ppbv yr−1, andincreasing ozone trends in the early morning and late afternoon. A monotonicallydecreasing trend (up to 0.5 ppbv yr−1) in the odd oxygen (Ox=O3+NO2) concentrations are simulated by CMAQ at all daytime hours.This result suggests that the increased ozone in the early morning and lateafternoon was likely caused by reduced NO–O3 titration, driven bycontinuous anthropogenic NOx emission reductions in the past decades.Furthermore, the CMAQ simulations revealed a shift in chemical regimes ofozone photochemical production. From 1990 to 2015, surface ozone productionin some metropolitan areas, such as Baltimore, has transited from aVOC-sensitive environment (>50 % probability) to aNOx-sensitive regime. Our results demonstrated that the long-termCWRF-CMAQ simulations can provide detailed information of the ozonechemistry evolution under a changing climate and may partially explain theUS ozone pollution responses to regional and national regulations.
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Conservation cobenefits from air pollution regulation: Evidence from birds
Massive wildlife losses over the past 50 y have brought new urgency to identifying both the drivers of population decline and potential solutions. We provide large-scale evidence that air pollution, specifically ozone, is associated with declines in bird abundance in the United States. We show that an air pollution regulation limiting ozone precursors emissions has delivered substantial benefits to bird conservation. Our estimates imply that air quality improvements over the past 4 decades have stemmed the decline in bird populations, averting the loss of 1.5 billion birds, ∼20% of current totals. Our results highlight that in addition to protecting human health, air pollution regulations have previously unrecognized and unquantified conservation cobenefits.
more » « less- NSF-PAR ID:
- 10202939
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 117
- Issue:
- 49
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 30900-30906
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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