Impacts of irrigation on ozone and fine particulate matter (PM2.5) air quality: Implications for emission control strategies for intensively irrigated regions in China

Abstract

Intensive irrigation is known to alleviate crop water stress and alter regional climate, which can in turn influence air quality, with ramifications for human health and food security. However, the interplay between irrigation, climate and air pollution especially in the simultaneously intensively irrigated and heavily polluted regions in China has rarely been studied. Here we incorporated a dynamic irrigation scheme into a regional climate-air quality coupled model to examine the potential impacts of irrigation on ozone (O3) and fine particulate matter (PM2.5) in China. Results show that irrigation increases PM2.5 by 12 μg m-3 (28 %) but reduces O3 concentration by 3-4 ppb (6 %-8 %). Among PM2.5, nitrate and ammonium aerosols rise by 70 % and 40 %, respectively, upon introducing irrigation, with secondary formation contributing to ~ 60 % and 10 %-30 %, respectively. High humidity and low temperature promote the formation of ammonium nitrate aerosols. To mitigate these adverse effects on PM2.5 air quality, we found that a 20 % reduction in NH3 and NOx emissions is more effective compared with individual emission reductions, while the enhancement in O3 due to the NOx reduction can be completely offset by irrigation itself. Our study highlights the potential benefits of irrigation regarding O3 pollution but potential problems regarding PM2.5 pollution under currently prevalent irrigation modes and anthropogenic emission scenarios, emphasizing the need for an integrated approach to balance water conservation, air pollution, climate change mitigation and food security in the face of development needs.