Impacts of irrigation on ozone and fine particulate matter (PM_2.5) 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 in especially 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 (PM_2.5) in China. Results show that irrigation increases the concentrations of primary air pollutants, but reduces O₃ concentration by 3–4 ppb. PM_2.5, nitrate and ammonium rise by 28 %, 70 % and 40 %, respectively, upon introducing irrigation, with secondary formation contributing to 5–10 %, ~60 %, and 10–30 %, respectively. High humidity and low temperature are the top two factors promoting the formation of ammonium nitrate aerosols. To mitigate these adverse effects on PM_2.5 air quality, we found that a 20 % combined reduction in NH₃ and NO_x emissions is more effective compared with individual emission reductions, while the enhancement in O₃ due to the NO_x reduction can be completely offset by irrigation itself. Our study highlights the potential benefits of irrigation regarding O₃ pollution but possible problems regarding PM_2.5 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.