Does Particulate Matter reduce Crop Yields on the North China Plain?

Abstract:

The North China Plain (NCP) is a key crop growing region, accounting for 45% of China’s maize production (Yang et al. 2015). It is vital to Chinese agriculture and the economy, encompassing the Beijing-Tianjin-Hebei megacity region. Anthropogenic factors are increasingly impacting crop yields, both globally, and in the NCP (Yuan et al. 2010). Particulate matter (PM) pollution is a significant problem in this region, where an annual average concentration of 108±34μg/m³ of fine particulate matter (PM2.5) was recorded for the Beijing-Tianjin-Hebei megacity region between 2013-18 (Zhai et al., 2019) , over three times the Chinese national air quality standard. Light absorption by PM reduces total shortwave radiation (SW), limiting plant productivity. However, PM also scatters incoming SW, increasing the diffuse fraction which is believed to increase growth and biomass assimilation.

To explore these competing effects, we employ the JULES-crop model to assess the impact of variations in SW and diffuse fraction on NCP maize yields. We find that any gains to NCP maize yields from aerosol-induced increases in diffuse fraction are outweighed by reductions in SW. As total atmospheric aerosol over the NCP is strongly linked to PM concentration, we conclude that current PM pollution in the region affects crop productivity.

We find the NCP maize crop to be most sensitive to changes in light intensity and quality during the early reproductive stage of development (July-August) when the effect on maize yields is up to 6.7% more than in other periods. We estimate increases in maize yields of approximately 3% if NCP PM pollution were reduced to that of comparable city regions worldwide, resulting in gains of 8Mt if applied across the country. Our results suggest that a reduction in PM pollution in the NCP during the early reproductive phase of maize development could increase yields, improving national food security.