亚热带稻区氨浓度多时间尺度变化及其干沉降

Multi-time Scale Variation of Atmospheric Ammonia Concentration and Dry Deposition in a Paddy Rice Region in Subtropical China

气象因子与人为活动显著影响大气氨浓度及其干沉降.目前,有关大气氨浓度的月尺度的时空变异特征有较多研究,而关于小时及日尺度等更精细时间尺度的大气浓度的变化特征及影响因素还不清楚.选取湖南省长沙县一个典型双季稻区,采用快速NH_(3)分析仪和小型气象站对大气NH_(3)浓度与相关气象因子进行为期1a的在线连续监测,对不同时间尺度(小时、日、月)下大气氨浓度、气象影响因子与干沉降通量进行分析.主要结果如下:稻区全年ρ(NH_(3))日平均值(以N计,下同)变化范围在0.01~58.0μg·m^(-3),年平均值为5.3μg·m^(-3).从小时尺度来看,大气NH_(3)浓度24 h动态均呈现单峰型,在不同季节峰值出现的时间存在差异,冬季较其余3个季节滞后.从日尺度来看,NH_(3)浓度主要受稻区施肥影响,在施肥后1~3d出现高峰,其后逐渐下降.从月尺度来看,ρ(NH_(3))月平均值在7月达到峰值,为12.8μg·m^(-3);10月为1.6μg·m^(-3),为谷值.从小时尺度看,NH_(3)浓度受气象因子的影响因季节发生变化,主要表现为:四季中NH_(3)浓度与空气温度、太阳辐射均表现出显著正相关,在春夏两季,与风速呈显著正相关,而除冬季外其与空气相对湿度呈显著负相关.从日尺度看,NH_(3)浓度与空气温度、降雨量和太阳辐射均呈显著正相关,而与相对湿度呈显著负相关.在月尺度上,各单个气象因子与NH_(3)浓度无显著相关性.干沉降计算结果表明,以小时平均NH_(3)浓度计算得到的干沉降通量(以N计)为8.5kg·(hm^(2)·a)^(-1),比以日平均计算的年通量高11.6%,比以月平均计算的年通量高12.4%.综上所述,亚热带稻区氨气浓度存在显著日变化和季节变化,加强氨气浓度的小时尺度观测,有助于揭示氨气浓度的多时间尺度变化特征和更准确定量氨气干沉降.

Meteorological factors and anthropogenic activities significantly affect atmospheric ammonia(NH_(3))concentration and its dry deposition.Former studies have examined the spatial and temporal variability in atmospheric NH_(3)concentrations at monthly scales.However,the characteristics of atmospheric concentrations at finer time scales such as hourly and daily scales and the influencing factors remain unclear.In this study,atmospheric NH_(3)concentration and related meteorological factors were continuously monitored online for one year in a double cropping rice region in subtropical China,and atmospheric NH_(3)concentration and its meteorological influencing factors as well as dry deposition were analyzed at different time scales(hourly,daily,and monthly).The main results were as follows:The annual average daily concentration of NH_(3)in the rice area varied from 0.01 to 58.0µg·m^(-3)(in N,same below),and the annual average concentration was 5.3µg·m^(-3).On the hourly scale,the 24-hour dynamics of atmospheric NH_(3)concentration showed a unimodal pattern,and the time of the NH_(3)peak appearance in different seasons was different;the time of the peak that appeared in winter lagged behind that in the other seasons.From the perspective of daily scale,NH_(3)concentration was mainly affected by fertilization in the paddy fields,peaking at 1-3 days after fertilization and then gradually decreasing.On the monthly scale,NH_(3)concentration peaked at 12.8µg·m^(-3)in July and was the lowest in October at 1.6µg·m^(-3).On the hourly scale,NH_(3)concentration varied seasonally due to the influences of meteorological factors,mainly as follows:NH_(3)concentration showed significant positive correlations with air temperature and solar radiation in all four seasons and with wind speed in spring and summer,whereas it showed significant negative correlations with relative humidity except in winter.On the daily scale,NH_(3)concentration showed a significant positive correlation with air temperature,rainfall,and solar radiation,whereas it showed a significant negative correlation with relative humidity.On the monthly scale,no significant correlation existed between each meteorological factor and NH_(3)concentration.The annual dry deposition flux(in N)calculated from the hourly average NH_(3)concentration was 8.5 kg·(hm^(2)·a)^(-1),which was 11.6%higher than the annual flux calculated from the daily average and 12.4%higher than the annual flux calculated from the monthly average.In summary,there were significant daily and seasonal variations in atmospheric NH_(3)concentration in the paddy rice region in subtropical China,and conducting hourly-scale observations of NH_(3)concentration can help to reveal the multi-time scale variations in NH_(3)concentration and to quantify NH_(3)dry deposition more accurately.