Inferring dust composition from wavelength‐dependent absorption in Aerosol Robotic Network (AERONET) data
Inferring dust composition from wavelength‐dependent absorption in Aerosol Robotic Network (AERONET) data
复制标题
DOI：
10.1029/2005jd006678
复制
发表时间：
2006-07
影响因子：
--
通讯作者：
C. Koven;I. Fung
中科院分区：
文献类型：
--
作者：
C. Koven;I. Fung
[1]大气矿物尘埃是地球系统的重要组成部分，影响气候和生物地球化学循环。我们提出了一种逆方法推断尘埃成分的光吸收的波长依赖性和气溶胶组分的复折射率。具体来说，我们将黑碳的吸收与赤铁矿和有机碳的吸收分开。我们将这种方法应用于粗模式为主的气溶胶机器人网络（AERONET）的观测在“尘埃带”区域的地球仪，我们确定灰尘的光学性质和成分在不同的位置之间的差异。我们解决粉尘成分使用两个相反的，括号内的矿物混合状态的假设：纯粹的内部混合和纯粹的外部混合。我们发现，计算出的绝对赤铁矿浓度是高度敏感的混合假设，而相对的地理和季节性模式是不太敏感的混合假设。内部混合计算似乎低估了绝对赤铁矿浓度，而外部混合高估了赤铁矿浓度。反演计算假设外部混合能够更好地解释波长依赖性的灰尘吸收，只有不同的赤铁矿浓度比反演使用内部混合，这需要大量的黑碳和赤铁矿之间的协变，以配合观测。撒哈拉和东亚的沙尘中赤铁矿含量高于阿拉伯的沙尘。撒哈拉沙尘还显示出赤铁矿含量的季节性变化，这可能反映了沙尘源区的季节性变化。
[1] Atmospheric mineral dust is an important component of the Earth system, affecting climate and biogeochemical cycling. We present an inverse method of inferring dust composition from wavelength dependence of light absorption and the complex refractive indices of aerosol components. Specifically, we separate absorption by black carbon from absorption by hematite and organic carbon. We apply this method to coarse-mode-dominated Aerosol Robotic Network (AERONET) observations in the “dust belt” region of the globe, and we identify differences between dust optical properties and composition in different locations. We solve for dust composition using two opposite, bracketing hypotheses of the state of mineralogical mixing: purely internal mixing and purely external mixing. We find that calculated absolute hematite concentrations are highly sensitive to mixing assumptions, while relative geographic and seasonal patterns are less sensitive to mixing assumptions. Internal mixing calculations appear to underestimate absolute hematite concentrations, while external mixing overestimates hematite concentrations. Inversions calculated assuming external mixing are better able to explain the wavelength dependence of dust absorption by only varying hematite concentration than inversions using internal mixing, which require substantial covariation between black carbon and hematite to match observations. Saharan and East Asian dust show higher hematite content than dust from Arabia. Saharan dust also shows seasonal variation in hematite content which may reflect seasonal shifts in dust source areas.