Atmospheric Deposition HNO3 Dry Deposition Fluxes in 1998

The role of urban vegetation on NOx-derived dry deposition fluxes was investigated for the arid Phoenix (Arizona, USA) metropolitan area using the Community Multiscale Air Quality Model (CMAQ) (9-13 June 1998). A new land cover classification and updated land cover data were introduced in the model to account for spatial extent and heterogeneity of urban land cover. Adjustments were made in the deposition velocity calculations to consider the adaptation of local plants to the environmental conditions of Central Arizona. According to the simulations 25 percent of the NOx derived dry deposition fluxes in the urban area were deposited on vegetation. When urban vegetation was excluded from the simulations NO2 deposition was reduced by 57 percent because of the significantly lower deposition velocities of impervious compared to vegetated surfaces; nitric acid deposition was relatively unchanged. Using a diagnostic model with input data from urban air quality monitoring sites, hourly NO and NO2 dry N deposition fluxes were simulated for the entire year 1998 to ~6 kg ha-1 yr-1. Dry deposition declined during the summer months, due to lower pollutant concentrations and temperature-induced closure of the plant stomata during afternoon hours.

本研究以美国亚利桑那州干旱城市凤凰城都会区为研究对象，采用多尺度空气质量模型（Community Multiscale Air Quality Model, CMAQ），于1998年6月9日至13日期间，探究了城市植被对氮氧化物（NOₓ）源性干沉降通量的调控作用。本研究在模型中引入全新的土地覆盖分类方案与更新后的土地覆盖数据，以表征城市土地覆盖的空间范围与异质性特征。同时对沉降速度的计算方法进行了调整，以适配亚利桑那州中部本土植物对当地环境条件的适应性。模拟结果表明，该都会区氮氧化物源性干沉降通量中有25%沉降于植被表面。若在模拟中移除城市植被因子，二氧化氮（NO₂）的沉降量将降低57%，这是由于不透水表面的沉降速度显著低于植被覆盖表面；而硝酸沉降量则基本保持不变。本研究基于城市空气质量监测站点的输入数据，采用诊断模型对1998年全年的逐小时一氧化氮（NO）与二氧化氮（NO₂）的氮干沉降通量进行模拟，结果显示其通量约为6千克每公顷每年（6 kg·ha⁻¹·yr⁻¹）。夏季干沉降通量有所下降，这是由于夏季污染物浓度降低，且午后气温升高会导致植物气孔关闭。