Abstract
Abstract. Brown carbon (BrC), a certain group of organic carbon (OC) with strong absorption from the visible (VIS) to ultraviolet (UV) wavelengths, makes a considerable contribution to light absorption on both global and regional scales. A high concentration and proportion of OC has been reported in China, but studies of BrC absorption based on long-term observations are rather limited in this region. In this study, we reported 3-year results of light absorption of BrC based on continuous measurement at the Station for Observing Regional Processes of the Earth System (SORPES) in the Yangtze River Delta, China, combined with Mie theory calculation. Light absorption of BrC was obtained using an improved absorption Ångström exponent (AAE) segregation method. The AAE of non-absorbing coated black carbon (BC) at each time step is calculated based on Mie theory simulation, together with single particle soot photometer (SP2) and aethalometer observations. By using this improved method, the variation of the AAE over time is taken into consideration, making it applicable for long-term analysis. The annual average light absorption coefficient of BrC (babs_BrC) at 370 nm was 6.3 Mm−1 at the SORPES station. The contribution of BrC to total aerosol absorption (PBrC) at 370 nm ranged from 10.4 to 23.9 % (10th and 90th percentiles, respectively), and reached up to ∼ 33 % in the open-biomass-burning-dominant season and winter. Both babs_BrC and PBrC exhibited clear seasonal cycles with two peaks in later spring/early summer (May–June, babs_BrC ∼ 6 Mm−1, PBrC ∼ 17 %) and winter (December, babs_BrC ∼ 15 Mm−1, PBrC ∼ 22 %), respectively. Lagrangian modeling and the chemical signature observed at the site suggested that open biomass burning and residential coal/biofuel burning were the dominant sources influencing BrC in the two seasons, respectively.
Highlights
Atmospheric aerosols cause adverse impacts on human health, but they alter earth’s radiation balance through their strong light scattering and absorption, substantially influencing regional and even global climate change (IPCC, 2013; Dockery et al, 1993; Wang et al, 2017b)
It is mentioned that Black carbon (BC) morphology can affect the AAE (Liu et al, 2015) and it is possible to overestimate brown carbon (BrC) absorption; the complex morphology can vary with time and currently it is hard to evaluate its quantitative effect
The result shows that babs_BrC / K+ ratio of June and December shows a significant difference, indicating that the dominant emission source of BrC in December is not open biomass burning
Summary
Atmospheric aerosols cause adverse impacts on human health, but they alter earth’s radiation balance through their strong light scattering and absorption, substantially influencing regional and even global climate change (IPCC, 2013; Dockery et al, 1993; Wang et al, 2017b). A certain type of organic aerosol defined as brown carbon (BrC) was revealed to be of strong light-absorbing efficiency (Formenti et al, 2003; Pöschl, 2003; Andreae and Gelencser, 2006; Kirchstetter et al, 2004; Mukai and Ambe, 1986; Patterson and McMahon, 1984), which can cause perturbations on radiation transfer similar to BC. This implies that the aerosol cooling effect could be overestimated by ignoring the light absorption from. The contribution of BrC to light absorption is estimated based on 3-year observations, and the potential sources of BrC in typical seasons are discussed
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