Impacts of the heterogeneous ammonia uptake on air quality in the North China Plain

Previous studies have revealed that the heterogeneous uptake of ammonia (NH ₃ ) on secondary organic aerosols (SOA) may influence the NH ₃  budget, nitrate aerosol chemistry, and the regional PM _2.5  burden, also constituting an important source of nitrogen-containing organic compounds (NOCs). However, regional modeling remains hindered by large uncertainties in the uptake coefficient ( γ ) and limited field-based constraints. In this study, we incorporate a first-order NOCs-forming NH ₃ –SOA reactive-uptake pathway into WRF-Chem and adopt a literature-based sensitivity range of γ=10-5-10-3 to evaluate its impacts on air quality and particulate organic nitrogen over the North China Plain during November 2017. Laboratory evidence of declining reaction efficiency and comparison with the measured NOCs burden support considering γ=10-5 as a conservative upper limit for sustained operation of this pathway under the conditions examined. With γ=10-5, the uptake reaction decreases NH ₃ concentrations by 0.62 % and inorganic aerosol and PM _2.5 concentrations by less than 0.06 %, while producing 1.2 µg m ⁻³ of NOCs in the NCP. These results indicate that the pathway has only a minor influence on NH ₃ and PM _2.5 under the present conditions, but may provide an additional source of particulate organic nitrogen.