Evaluation of the control effectiveness in mitigation acid deposition in a valley city in China

Abstract

In valley cities, gaseous precursors emitted from near-source can rapidly deposit and give rise to localized acid rain. The presence of local slope changes and convective meteorology facilitates the convergence of pollutants, thereby reducing the likelihood of atmospheric SO${}_2$ and NO${}_x$ being transported to other regions through atmospheric movement, while increasing their susceptibility to exacerbating the acid deposition process. In our study, a decade-long dataset of precipitation samples was collected and analyzed. Subsequently, emission scenarios were simulated using high-resolution nested domains in the meteorological field-driven source-directed CMAQ model generated by the WRF model. Our findings demonstrate that effective management of regional SO${}_2$ emissions plays a pivotal role in regulating precipitation pH. Two control scenarios (reduction and relocation) conducted an evaluation and comparison of these approaches. The source reduction scenario effectively ensures that annual average SO${}_2$ levels remain below the threshold of 24 $\mu g/m^3$ by maintaining total industrial emissions below 2,561.62 tonnes. However, it is important to note that there are significant seasonal variations in industrial emission limits due to climate and precipitation. In the migration scenario (ignoring terrain), the environmental SO${}_2$ in the study area was significantly reduced by an average of 16 $\mu g/m^3$. Compared with source abatement, the relocation of energy-intensive industries to regions characterized by lower relative humidity mitigates pollution impacts on mountainous cities and ensures long-term economic benefits. Under complex terrain and small range of special meteorological conditions, the influencing factors of air pollution process and how to implement effective control strategies deserve continuous attention.