纱帽山不同海拔大气氮湿沉降通量差异及递变规律的数学模拟

Statistical modeling of variability of atmospheric nitrogen wet deposition fluxes along altitudinal gradients of Shamao mountain

通过对毕节市七星关区城郊纱帽山不同海拔大气沉降进行采样,检测了湿沉降中的水溶性总氮、铵态氮、亚硝态氮和硝态氮等指标.结果表明:①采样点位总氮湿沉降通量随海拔升高呈明显下降趋势,海拔每升高1 km年均垂直递减梯度为5.43 kg·hm-2·a-1.冬季山顶通量占最低海拔样点通量均值的29.23%,而夏季为87.80%.这是由季节性降水差异所导致的,夏季雨水冲并作用使得大气气溶胶浓度为全年最低(冬季最高),因此,在有限海拔高度内垂直梯度在夏季最小而冬季最大.②各路径不同程度地出现了沉降峰值带(步梯路除外),这与下垫面污染气体的垂直扩散有关.以车辆尾气为污染源,借助高斯模式推导其最大浓度出现的高度为56.11 m,而实测峰值带为理论计算高度的2~3倍,这与污染物扩散条件复杂及经验公式的非普适性有关.③铵态氮和硝态氮为无机氮的主要形式,亚硝态氮仅占9.04%,且冬季沉降量最大,这与氨氧化细菌在应对低温等不利环境方面有更强的适应性有关.④借助指数模型模拟了氮的湿沉降通量随海拔高度的递变规律,拟合公式为M=15.2534k·exp(-0.00079602x),随机检验拟合程度较高,具有实际应用价值和推广前景.

Using sampling atmospheric precipitation strategy along altitudinal gradients of Shamao Mountain,Qixingguan District,Bijie City,to assess the total dissolved nitrogen(TDN),ammonium nitrogen,nitrous nitrogen and nitrate nitrogen in wet deposition.The results showed that:①The wet deposition flux of total nitrogen was decreased with the elevation,and the annual average vertical declining gradient reached 5.43 kg·hm-2·a-1 per 1 km.The flux of the peak sampling point was accounted for 29.23%of the mean value at the lowest altitude sampling points in winter,while it was 87.80%in summer,as the results of the difference of seasonal precipitation characterized with the lowest of atmospheric aerosol concentration under the rainfall rinse effect in summer,vise verse in winter,making the lowest vertical gradient of wet deposition flux in summer and highest in winter within the limited altitude.②Different paths was presented inordinately with peaky curves of atmospheric deposition,which was related to the vertical diffusion of polluted gas on the underlying surface.With assuming the vehicle exhaust as the pollution source and using Gaussian theory of pollutants diffusion,the height of maximum pollutants concentration was 56.11 m.But then the measured peak-zone height was 2~3 times of the theoretical height,which was contributed possibly to the complexity of pollutant diffusion conditions and the non-universality of empirical formula summarized by the former.③Ammonium nitrogen and nitrate nitrogen were the main forms of inorganic nitrogen.Nitrous nitrogen was accounted for only 9.04%and its sediment amount reached peak in winter,which was related to the stronger adaptability of ammonia-oxidizing bacteria in adverse environment such as low temperature.④The model of atmospheric nitrogen wet deposition flux with altitude was constructed by exponential model.The formula was M=15.2534k·exp(-0.00079602x),and the high compliance of random test entitled the formula to be spread out in other study.