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Abstract. Our work explores the impact of two important dimensions of landsystem changes, land use and land cover change (LULCC) as well as directagricultural reactive nitrogen (Nr) emissions from soils, on ozone(O3) and fine particulate matter (PM2.5) in terms of air quality overcontemporary (1992 to 2014) timescales. We account for LULCC andagricultural Nr emissions changes with consistent remote sensingproducts and new global emission inventories respectively estimating theirimpacts on global surface O3 and PM2.5 concentrations as well as Nrdeposition using the GEOS-Chem global chemical transport model. Over thistime period, our model results show that agricultural Nr emissionchanges cause a reduction of annual mean PM2.5 levels over Europe andnorthern Asia (up to −2.1 µg m−3) while increasing PM2.5 levels in India, China and the eastern US (up to +3.5 µg m−3). Land cover changes induce small reductions in PM2.5 (up to −0.7 µg m−3) over Amazonia, China and India due to reduced biogenic volatile organic compound (BVOC) emissions and enhanced deposition of aerosol precursor gases (e.g., NO2, SO2). Agricultural Nr emissionchanges only lead to minor changes (up to ±0.6 ppbv) in annual meansurface O3 levels, mainly over China, India and Myanmar. Meanwhile, ourmodel result suggests a stronger impact of LULCC on surface O3 over the time period across South America; the combination of changes in drydeposition and isoprene emissions results in −0.8 to +1.2 ppbv surfaceozone changes. The enhancement of dry deposition reduces the surface ozone level (up to −1 ppbv) over southern China, the eastern US and central Africa. The enhancement of soil NO emission due to crop expansion also contributes to surface ozone changes (up to +0.6 ppbv) over sub-Saharan Africa. Incertain regions, the combined effects of LULCC and agricultural Nr emission changes on O3 and PM2.5 air quality can be comparable (>20 %) to anthropogenic emission changes over the same time period. Finally, we calculate that the increase in global agricultural Nr emissions leads to a net increase in global land area (+3.67×106km2) that potentially faces exceedance of the critical Nr load (>5 kg N ha−1 yr−1). Our result demonstrates the impacts of contemporary LULCC and agricultural Nr emission changes on PM2.5 and O3 in terms of air quality, as well as the importanceof land system changes for air quality over multidecadal timescales.
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Effects of urbanization on regional meteorology and air quality in Southern California
Abstract. Urbanization has a profound influence on regional meteorology and air qualityin megapolitan Southern California. The influence of urbanization onmeteorology is driven by changes in land surface physical properties and landsurface processes. These changes in meteorology in turn influence air qualityby changing temperature-dependent chemical reactions and emissions,gas–particle phase partitioning, and ventilation of pollutants. In this studywe characterize the influence of land surface changes via historicalurbanization from before human settlement to the present day on meteorology andair quality in Southern California using the Weather Research and ForecastingModel coupled to chemistry and the single-layer urban canopy model(WRF–UCM–Chem). We assume identical anthropogenic emissions for thesimulations carried out and thus focus on the effect of changes in landsurface physical properties and land surface processes on air quality.Historical urbanization has led to daytime air temperature decreases of up to1.4 K and evening temperature increases of up to 1.7 K. Ventilation of airin the LA basin has decreased up to 36.6 % during daytime and increasedup to 27.0 % during nighttime. These changes in meteorology are mainlyattributable to higher evaporative fluxes and thermal inertia of soil fromirrigation and increased surface roughness and thermal inertia frombuildings. Changes in ventilation drive changes in hourlyNOx concentrations with increases of up to 2.7 ppb duringdaytime and decreases of up to 4.7 ppb at night. Hourly O3concentrations decrease by up to 0.94 ppb in the morning and increase by upto 5.6 ppb at other times of day. Changes in O3 concentrations aredriven by the competing effects of changes in ventilation and precursorNOx concentrations. PM2.5 concentrations show slightincreases during the day and decreases of up to 2.5 µg m−3at night. Process drivers for changes in PM2.5 include modificationsto atmospheric ventilation and temperature, which impact gas–particle phasepartitioning for semi-volatile compounds and chemical reactions.Understanding process drivers related to how land surface changes effectregional meteorology and air quality is crucial for decision-making on urbanplanning in megapolitan Southern California to achieve regional climateadaptation and air quality improvements.
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- PAR ID:
- 10129212
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 19
- Issue:
- 7
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 4439 to 4457
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.5194/acp-19-4439-2019
