Modeling dry and wet deposition of sulfate, nitrate, and ammonium ions in Jiuzhaigou National Nature Reserve, China using a source-oriented CMAQ model: Part I. Base case model results

Abstract

A source-oriented Community Multiscale Air Quality (CMAQ) model driven by the meteorological fields generated by the Weather Research and Forecasting (WRF) model was used to study the dry and wet deposition of nitrate (NO3−), sulfate (SO42−), and ammonium (NH4+) ions in the Jiuzhaigou National Nature Reserve (JNNR), China from June to August 2010 and to identify the contributions of different emission sectors and source regions that were responsible for the deposition fluxes. The model performance is evaluated in this paper and the source contribution analyses are presented in a companion paper. The results show that WRF is capable of reproducing the observed precipitation rates with a Mean Normalized Gross Error (MNGE) of 8.1%. Predicted wet deposition fluxes of SO42− and NO3− at the Long Lake (LL) site (3100m a.s.l.) during the three-month episode are 2.75 and 0.34kgS(N) ha−1, which agree well with the observed wet deposition fluxes of 2.42 and 0.39kgS(N)ha−1, respectively. Temporal variations in the weekly deposition fluxes at LL are also well predicted. Wet deposition flux of NH4+ at LL is over-predicted by approximately a factor of 3 (1.60kgNha−1vs. 0.56kgNha−1), likely due to missing alkaline earth cations such as Ca2+ in the current CMAQ simulations. Predicted wet deposition fluxes are also in general agreement with observations at four Acid Deposition Monitoring Network in East Asia (EANET) sites in western China. Predicted dry deposition fluxes of SO42− (including gas deposition of SO2) and NO3− (including gas deposition of HNO3) are 0.12 and 0.12kgS(N)ha−1 at LL and 0.07 and 0.08kgS(N)ha−1 at Jiuzhaigou Bureau (JB) in JNNR, respectively, which are much lower than the corresponding wet deposition fluxes. Dry deposition flux of NH4+ (including gas deposition of NH3) is 0.21kgNha−1 at LL, and is also much lower than the predicted wet deposition flux. For both dry and wet deposition fluxes, predictions from the 12-km resolution nested domain are similar to those from the 36-km resolution parent domain.