Abstract. Dry deposition is a major sink of tropospheric ozone.Increasing evidence has shown that ozone dry deposition actively linksmeteorology and hydrology with ozone air quality. However, there is littlesystematic investigation on the performance of different ozone drydeposition parameterizations at the global scale and how parameterizationchoice can impact surface ozone simulations. Here, we present the results ofthe first global, multidecadal modelling and evaluation of ozone drydeposition velocity (vd) using multiple ozone dry depositionparameterizations. We model ozone dry deposition velocities over 1982–2011using four ozone dry deposition parameterizations that are representative ofcurrent approaches in global ozone dry deposition modelling. We useconsistent assimilated meteorology, land cover, and satellite-derived leafarea index (LAI) across all four, such that the differences in simulatedvd are entirely due to differences in deposition model structures orassumptions about how land types are treated in each. In addition, we usethe surface ozone sensitivity to vd predicted by a chemical transportmodel to estimate the impact of mean and variability of ozone dry depositionvelocity on surface ozone. Our estimated vd values from four differentparameterizations are evaluated against field observations, and whileperformance varies considerably by land cover types, our results suggestthat none of the parameterizations are universally better than the others.Discrepancy in simulated mean vd among the parameterizations isestimated to cause 2 to 5 ppbv of discrepancy in surface ozone in theNorthern Hemisphere (NH) and up to 8 ppbv in tropical rainforests in July,and up to 8 ppbv in tropical rainforests and seasonally dry tropical forestsin Indochina in December. Parameterization-specific biases based onindividual land cover type and hydroclimate are found to be the two maindrivers of such discrepancies. We find statistically significant trends inthe multiannual time series of simulated July daytime vd in allparameterizations, driven by warming and drying (southern Amazonia, southernAfrican savannah, and Mongolia) or greening (high latitudes). The trend inJuly daytime vd is estimated to be 1 % yr−1 and leadsto up to 3 ppbv of surface ozone changes over 1982–2011. The interannual coefficient ofvariation (CV) of July daytime mean vd in NH is found to be5 %–15 %, with spatial distribution that varies with the dry depositionparameterization. Our sensitivity simulations suggest this can contributebetween 0.5 to 2 ppbv to interannual variability (IAV) in surface ozone, butall models tend to underestimate interannual CV when compared to long-termozone flux observations. We also find that IAV in some dry depositionparameterizations is more sensitive to LAI, while in others it is more sensitiveto climate. Comparisons with other published estimates of the IAV ofbackground ozone confirm that ozone dry deposition can be an important partof natural surface ozone variability. Our results demonstrate the importanceof ozone dry deposition parameterization choice on surface ozone modellingand the impact of IAV of vd on surface ozone, thus making a strong casefor further measurement, evaluation, and model–data integration of ozone drydeposition on different spatiotemporal scales.
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The long-term trend and production sensitivity change in the US ozone pollution from observations and model simulations
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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- Award ID(s):
- 1639327
- NSF-PAR ID:
- 10157798
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 20
- Issue:
- 5
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 3191 to 3208
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-20-3191-2020
