Interpretation of measured aerosol mass scattering efficiency over North America using a chemical transport model
Interpretation of measured aerosol mass scattering efficiency over North America using a chemical transport model
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DOI：
10.5194/acp-19-2635-2019
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发表时间：
2019-02-28
影响因子：
6.3
通讯作者：
Martin, Randall, V
中科院分区：
文献类型：
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作者：
Latimer, Robyn N. C.;Martin, Randall, V
气溶胶质量散射效率影响气候强迫计算、大气能见度和对气溶胶光学厚度卫星观测的解释。我们评估了代表性的气溶胶质量散射效率（α（sp））的GEOS-Chem化学传输模型在北美使用同位测量气溶胶散射和质量从2000年和2010年之间的IMPROVE网络站点。我们发现了一个积极的偏见，在质量散射效率的气溶胶粒径分布和颗粒吸湿性的模型中给出当前的假设。我们发现，在干燥（RH <35%）和中等湿度（35% < RH <65%）条件下，质量散射效率的高估最为明显，偏差分别为82%和40%。为了解决这些偏差，我们调查了周围的两个最大的贡献者细气溶胶质量，有机（OA）和二次无机气溶胶（SIA）的假设。抑制SIA的吸湿增长低于35%RH和减少干燥的几何平均半径，从0.069亩为SIA和0.073亩为OA到0.058亩为两种气溶胶类型，显着降低了在IMPROVE网站在干燥条件下观察到的总体偏差从82%到9%。根据kappa-Kohler理论对次生无机（吸湿性参数kappa = 0.61）和有机（kappa = 0.10）气溶胶实施广泛使用的吸湿性增长替代表示法消除了α（sp）中剩余的总体偏倚。将气溶胶大小和吸湿性的这些变化模拟到GEOS-Chem模型中，导致北美上空模拟的年平均α（sp）增加了16%，在相对湿度和吸湿性气溶胶分数高的北方地区增加了25%至45%，在相对湿度低的美国西南部，α（sp）减少了15%。
Aerosol mass scattering efficiency affects climate forcing calculations, atmospheric visibility, and the interpretation of satellite observations of aerosol optical depth. We evaluated the representation of aerosol mass scattering efficiency (alpha(sp)) in the GEOS-Chem chemical transport model over North America using collocated measurements of aerosol scatter and mass from IMPROVE network sites between 2000 and 2010. We found a positive bias in mass scattering efficiency given current assumptions of aerosol size distributions and particle hygroscopicity in the model. We found that overestimation of mass scattering efficiency was most significant in dry (RH < 35 %) and midrange humidity (35% < RH < 65 %) conditions, with biases of 82% and 40 %, respectively. To address these biases, we investigated assumptions surrounding the two largest contributors to fine aerosol mass, organic (OA) and secondary inorganic aerosols (SIA). Inhibiting hygroscopic growth of SIA below 35% RH and decreasing the dry geometric mean radius, from 0.069 mu m for SIA and 0.073 mu m for OA to 0.058 mu m for both aerosol types, significantly decreased the overall bias observed at IMPROVE sites in dry conditions from 82% to 9 %. Implementation of a widely used alternative representation of hygroscopic growth following kappa-Kohler theory for secondary inorganic (hygroscopicity parameter kappa = 0.61) and organic (kappa = 0.10) aerosols eliminated the remaining overall bias in alpha(sp). Incorporating these changes in aerosol size and hygroscopicity into the GEOS-Chem model resulted in an increase of 16% in simulated annual average alpha(sp) over North America, with larger increases of 25% to 45% in northern regions with high RH and hygroscopic aerosol fractions, and decreases in alpha(sp) up to 15% in the southwestern U.S. where RH is low.