Atmospheric ammonia and particulate inorganic nitrogen over the United States
Atmospheric ammonia and particulate inorganic nitrogen over the United States
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DOI：
10.5194/acp-12-10295-2012
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发表时间：
2012-01-01
影响因子：
6.3
通讯作者：
Pye, H. O. T.
中科院分区：
文献类型：
--
作者：
Heald, C. L.;Collett, J. L., Jr.;Pye, H. O. T.
我们使用来自受保护的视觉环境跨部门监测（IMPROVE）网络、中西部氨监测项目、11个地面站点活动以及红外大气探测干涉仪（IASI）卫星测量的原位观测数据，利用GEOS-Chem模型研究美国上空的无机气溶胶负荷和大气氨浓度。IASI的观察表明，目前加州和中西部春季的氨排放量被低估了。在加州，这种低估可能导致GEOS-Chem模型中硝酸盐形成的低估。然而，在其余的美国大陆，我们发现硝酸盐模拟全年都有很高的偏差（标准化平均偏差> = 1.0），除了春季（由于这个季节氨的低估）。前驱体排放、气溶胶对N2O5的吸收效率、OH浓度、硝酸形成的反应速率或硝酸的干沉积速度等方面的不确定性都不能解释这种偏差。我们发现，在美国，将硝酸浓度降低到模拟值的75%可以纠正硝酸盐（以及铵）的偏差。然而，这种潜在减少的机制尚不清楚，可能是化学、沉积和亚网格近地表梯度误差的结合。这个“更新”的模拟再现了PM和氨负荷，并捕捉了美国各地气体-颗粒分配的强烈季节性和空间梯度。我们估计氮占美国无机细颗粒物质量的15-35%，并且随着硫排放的减少和氨排放的增加，这一比例在未来十年可能会增加。
We use in situ observations from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network, the Midwest Ammonia Monitoring Project, 11 surface site campaigns as well as Infrared Atmospheric Sounding Interferometer (IASI) satellite measurements with the GEOS-Chem model to investigate inorganic aerosol loading and atmospheric ammonia concentrations over the United States. IASI observations suggest that current ammonia emissions are underestimated in California and in the springtime in the Midwest. In California this underestimate likely drives the underestimate in nitrate formation in the GEOS-Chem model. However in the remaining continental United States we find that the nitrate simulation is biased high (normalized mean bias > = 1.0) year-round, except in Spring (due to the underestimate in ammonia in this season). None of the uncertainties in precursor emissions, the uptake efficiency of N2O5 on aerosols, OH concentrations, the reaction rate for the formation of nitric acid, or the dry deposition velocity of nitric acid are able to explain this bias. We find that reducing nitric acid concentrations to 75% of their simulated values corrects the bias in nitrate (as well as ammonium) in the US. However the mechanism for this potential reduction is unclear and may be a combination of errors in chemistry, deposition and sub-grid near-surface gradients. This "updated" simulation reproduces PM and ammonia loading and captures the strong seasonal and spatial gradients in gas-particle partitioning across the United States. We estimate that nitrogen makes up 15-35% of inorganic fine PM mass over the US, and that this fraction is likely to increase in the coming decade, both with decreases in sulfur emissions and increases in ammonia emissions.