Variability of Aerosol Liquid Water Content in Pm2.5 and Related Influential Factors During Long-Term Observations in Beijing

Abstract Aerosol liquid water content (ALWC) has important influences on atmospheric radiation and aerosol chemical processes. However, the characteristics of ALWC based on long-term observation rarely had a systematic analysis in Beijing, China. In this work, the seasonal variation of ALWC in PM2.5 were investigated based on hourly monitoring of inorganic water-soluble ions and their gaseous precursors using thermodynamic model ISORROPIA II. The results showed that the ALWC concentrations exhibited pronounced seasonal (autumn>summer>spring>winter) and diurnal variation trends. The sensitivity tests indicated that ALWC depended strongly on ambient RH, followed by total sulfate (TSO4) and total nitrate (TNO3). With increasing of RH, the ALWC showed an exponential growth trend in all four seasons. The long-term analysis data showed that the ALWC increased from 2.92 μg·m-3 to 75.83 μg·m-3 when ambient RH spanned 30% up to 90%, associating with the sulfate, nitrate and ammonium (abbreviated as SNA) mass fraction in PM2.5 rose from 0.39 to 0.58 in the atmosphere. The ALWC facilitated the formation of SNA through gas-particle partitioning and conversion. The self-amplifying processes between ALWC and SNA could promote more aerosol formation. By modeling ALWC under different seasonal atmospheric scenarios, it was found that reductions in chemical species could reduce ALWC concentrations in different degrees. Based on the current emission condition, controlling excess NH3 emission could effectively reduce ALWC with at most of 45.71% in summer, indicated that controlling emission of excess NH3 would effectively reduce ALWC and PM2.5 concentrations under high levels of SO42- and NO3-