南海大气二氧化氮时空分布特征及其对海表叶绿素a浓度的影响

Atmospheric Nitrogen Dioxide over the South China Sea:Spatial-temporal Distribution and Impact on Sea Surface Chlorophyll-a Concentration

【目的】研究南海上层大气NO_(2)柱浓度的时空分布特征及其影响因素,探讨南海大气氮沉降通量及其对海表叶绿素a浓度的影响。【方法】使用2005—2020年大气NO_(2)柱浓度的OMI遥感产品、ERA-5再分析降水数据、边界层高度数据、风速数据以及海洋表层叶绿素a浓度月平均遥感数据,分析南海大气氮沉降通量及其对海表叶绿素a的影响。【结果与结论】南海附近区域大气高浓度NO_(2)主要分布在珠江三角洲。NO_(2)浓度随季节变化较大的区域主要分布在南海北部陆地、陆架;其余海域大气中NO_(2)浓度终年较低。珠江三角洲附近大气NO_(2)柱浓度高值出现在12月及次年1月,年平均氮沉降通量均值为13.50kg·hm^(-2)。南海北部陆架大气的NO_(2)柱浓度峰值出现在3月,氮沉降通量年平均值为4~8kg·hm^(-2),其余海域的NO_(2)柱浓度峰值则出现在3月或4月,氮沉降通量年平均值为0.5kg·hm^(-2)。NO_(2)柱浓度主要受到降水和风速的共同影响,其中,降水通过淋溶作用消耗NO_(2),风则通过稀释作用降低NO_(2)柱浓度,同时,冬季季风还可将南海北部陆地空气中的高浓度NO_(2)输送到南海。强厄尔尼诺事件过后的春季由于中南半岛生物质燃烧的增加以及珠江三角洲区域降水量增加,使得氮沉降通量出现明显增加。吕宋海峡西部,氮沉降能造成约10%的叶绿素a浓度增加。

【Objective】This study aims to examine the spatiotemporal distribution characteristics of upper atmospheric NO_(2)column concentration over the South China Sea and identify its influencing factors.Additionally,it seeks to investigate the potential impact of atmospheric nitrogen deposition flux on sea surface chlorophyll-a level.【Method】We utilized OMI remote sensing products of atmospheric NO_(2)column concentration from 2005 to 2020.We also incorporated ERA-5 reanalysis precipitation data,boundary layer height data,wind speed data,and monthly average remote sensing data of sea surface chlorophyll-a concentration.Through the analysis of these datasets,we explored the patterns of atmospheric nitrogen deposition flux in the South China Sea and its relationship with sea surface chlorophyll-a concentration.【Result and Conclusion】The high atmospheric NO_(2)concentrations near the South China Sea are mainly distributed over the Pearl River Delta in China.The regions with significant seasonal concentration variations are distributed primarily over the land and shelf areas in the northern part of the South China Sea,and the atmospheric NO_(2)concentrations over the rest of the sea are low all year round.The peak NO_(2)column concentration near the Pearl River Delta occurs in December and January of the following year,with an annual average nitrogen deposition flux of 13.50 kg·hm^(-2).The peak NO_(2)column concentration over the northern shelf of the South China Sea occurs in March,with an annual average nitrogen deposition flux of 4-8 kg·hm^(-2).In the remaining regions of the sea,the peak NO_(2)column concentration is observed in March or April,and the annual average nitrogen deposition flux is around 0.5 kg·hm^(-2).The NO_(2)column concentration is mainly influenced by precipitation and wind speed,where precipitation consumes NO_(2)by leaching and wind reduces NO_(2)column concentration by dilution.The winter monsoon transports high NO_(2)concentrations from land-based air over the northern part of the South China Sea to the South China Sea.A significant increase in nitrogen deposition flux occurs in the spring after the intense El Nino event due to the increased biomass burning in the South-Central Peninsula.In the western Luzon Strait,nitrogen deposition can cause 10%increase chlorophyll-a concentration.