Nitrous acid emission from soil bacteria and related environmental effect over the North China Plain

Soil bacteria could be one of the important sources for ambient HONO. However, the HONO emission from soil bacteria over North China Plain (NCP) with vast croplands has not yet been evaluated. In this study, high-resolution simulations are created to explore the HONO emission from soil bacteria over NCP and related in-fluences on atmospheric chemistry. Ground measurements of critical air pollutants including O-3, HONO, and PM2.5 compositions are incorporated to constrain the model simulations. Results show that abundant HONO is emitted from soil bacteria over NCP during summertime and the emission rate varies dramatically for different areas (about 0.2 kg km(-2) d(-1) - 2.0 kg km(-2) d(-1)). The HONO emission rate presents clear diurnal cycles with peaks of 1.5 kg km(-2) d(-1) in the afternoon and valleys of 0.4 kg km(-2) d(-1) during the early morning hours. The resulting HONO concentration ranges from 0.2 mu g m(-3) to 1.4 mu gm(-3), which predominates the total HONO concentration in ambient air, particularly in western NCP. The soil bacteria source can significantly alter the diurnal cycles of ambient HONO and OH concentrations over NCP, but only slightly change O-3 and PM2.5 concentrations via participating photochemistry and secondary aerosol formations. These results highlight the pressing need for the involvement of HONO emission from soil bacteria in modeling studies regarding atmo-spheric chemistry, particularly in rural areas.

Automated summary

The study shows that soil bacteria in the North China Plain emit abundant HONO during the summer, with varying emission rates across different areas and clear diurnal cycles. HONO emissions from soil bacteria significantly affect atmospheric chemistry in the region, particularly in altering diurnal cycles of HONO and OH concentrations.