地壳元素铁的吸光贡献对黑碳吸光增强估算的影响——以武汉为例

传统方法使用固定的波长吸收指数来估算地壳元素或棕碳吸光,但该方法只能处理仅存在两种组分的情形(黑碳/棕碳,或黑碳/地壳元素)的吸光贡献,存在较大不确定性.为此,本文提出一种新的方法,利用武汉在线观测数据(2021年2、3、8、9月),采用铁作为地壳元素的示踪物,利用最小相关系数法(MRS)得出地壳元素的吸光贡献,在扣除地壳元素吸光之后,再得到黑碳吸光增强系数(E_abs).结果显示观测期间370nm波段地壳元素吸光贡献均值为12.3%,月均值范围5.7%~15.5%,且波长吸收指数与铁的浓度正相关,表明地壳元素吸光贡献不可忽视.地壳元素吸光贡献呈现出显著的季节特征,呈现出冬季低,春季高的特点.地壳元素吸光的分离前后计算的E_abs存在一定的差异,受到了黑碳和铁的相关性的影响.观测期间扣除地壳元素吸光后,E_abs均值为1.43±0.53,在季节性上呈现春夏高,秋冬低的特性,春季较高E_abs值与春季黑碳较高的老化程度有关.E_abs对无机盐和有机物的含量存在正的依赖关系,证明了这些包裹物质对吸光增强的影响.

Determination of crustal element iron light absorption contribution and effects on black carbon light absorption enhancement estimation: a case study in Wuhan

The traditional method uses empirical absorption Ångström exponent to estimate the light absorption of crustal elements or brown carbon, and this method can only handle the two components scenario (blackcarbon/brown carbon or blackcarbon/crustal elements), leading to substantial uncertainties. This study introduces a new method that uses the Fe as the crustal element tracer. Using measurement data in Wuhan (February, March, August, and September 2021) by applying the minimum R-squared method (MRS), the crustal elements light absorption contribution can be obtained. After subtracting the crustal elements light absorption, absorption enhancement factor (E_abs) can be obtained. The results showed that the average crustal elements absorption contribution at 370nm during the observation period was 12.3%, with a monthly average ranging from 5.7% to 15.5%. Meanwhile, AAE exhibited a positive dependence on the concentration of Fe. These collective clues indicate that the crustal elements absorption contribution cannot be ignored. Crustal elements light absorption demonstrated a considerable seasonality, which was low in winter and high in spring. There are deviations in the calculated E_abs before and after the separation of crustal elements light absorption, which is influenced by the correlation between blackcarbon and iron. During the observation period, after deducting the light absorption of crustal elements, the average E_abs was 1.43±0.53, and E_abs was high in spring and summer, and low in autumn and winter. HighE_abs in spring was associated with a higher degree of BC aging. The analysis found that E_abs demonstrated a positive dependence on the content of inorganic salts and organic matters, which proves the influence of these coating materials on the enhancement of light absorption.