Examining the competing effects of contemporary land management vs. land cover changes on global air quality

Wong, Anthony Y. H.; Geddes, Jeffrey A.

Our work explores the impact of two important dimensions of land system changes, land use and land cover change (LULCC) as well as direct agricultural reactive nitrogen (Ninline-formular) emissions from soils, on ozone (Oinline-formula3) and fine particulate matter (PMinline-formula2.5) in terms of air quality over contemporary (1992 to 2014) timescales. We account for LULCC and agricultural Ninline-formular emissions changes with consistent remote sensing products and new global emission inventories respectively estimating their impacts on global surface Oinline-formula3 and PMinline-formula2.5 concentrations as well as Ninline-formular deposition using the GEOS-Chem global chemical transport model. Over this time period, our model results show that agricultural Ninline-formular emission changes cause a reduction of annual mean PMinline-formula2.5 levels over Europe and northern Asia (up to inline-formula−2.1 inline-formulaµg minline-formula−3) while increasing PMinline-formula2.5 levels in India, China and the eastern US (up to inline-formula+3.5 inline-formulaµg minline-formula−3). Land cover changes induce small reductions in PMinline-formula2.5 (up to inline-formula−0.7 inline-formulaµg minline-formula−3) over Amazonia, China and India due to reduced biogenic volatile organic compound (BVOC) emissions and enhanced deposition of aerosol precursor gases (e.g., NOinline-formula2, SOinline-formula2). Agricultural Ninline-formular emission changes only lead to minor changes (up to inline-formula±0.6 ppbv) in annual mean surface Oinline-formula3 levels, mainly over China, India and Myanmar. Meanwhile, our model result suggests a stronger impact of LULCC on surface Oinline-formula3 over the time period across South America; the combination of changes in dry deposition and isoprene emissions results in inline-formula−0.8 to inline-formula+1.2 ppbv surface ozone changes. The enhancement of dry deposition reduces the surface ozone level (up to inline-formula−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 inline-formula+0.6 ppbv) over sub-Saharan Africa. In certain regions, the combined effects of LULCC and agricultural Ninline-formular emission changes on Oinline-formula3 and PMinline-formula2.5 air quality can be comparable (inline-formula>20 %) to anthropogenic emission changes over the same time period. Finally, we calculate that the increase in global agricultural Ninline-formular emissions leads to a net increase in global land area (inline-formula M36inlinescrollmathml + normal 3.67 × normal 10 normal 6 0.125emnobreak normal km normal 2 80pt14ptsvg-formulamathimg09bdf3dd009e61d7f0320d163dde59c0 acp-21-16479-2021-ie00001.svg80pt14ptacp-21-16479-2021-ie00001.png ) that potentially faces exceedance of the critical Ninline-formular load (inline-formula>5 kg N hainline-formula−1 yrinline-formula−1). Our result demonstrates the impacts of contemporary LULCC and agricultural Ninline-formular emission changes on PMinline-formula2.5 and Oinline-formula3 in terms of air quality, as well as the importance of land system changes for air quality over multidecadal timescales.

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Wong, Anthony Y. H. / Geddes, Jeffrey A.: Examining the competing effects of contemporary land management vs. land cover changes on global air quality. 2021. Copernicus Publications.

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