The Contribution of Black Carbon and Non-BC Absorbers on Aerosol Absorption Coefficient in Nanjing, China

Ari Leskinen,Die Fang,Jorma Jokiniemi,Maija-Riitta Hirvonen,Antti Ruuskanen,Yu Zhao,Qinqeng Wang,Kari E J Lehtinen,Pekka Kolmonen,Mika Komppula,Cheng Gu,Sami Romakkaniemi

doi:10.4209/aaqr.2019.06.0326

Abstract

An aethalometer was employed in a 1-year campaign (November 2014–November 2015) in Nanjing, China, that aimed to estimate the contributions of black carbon (BC; annual average ± std = 4.0 ± 3.3 µg m–3) and non-BC absorbers, such as brown carbon, to the aerosol absorption coefficient. We applied two methods: 1) the traditional calculation from the aethalometer data, assuming an absorption Ångström exponent (AAE) of unity for BC (“AE method”), which provided an overall average of 27.2% for the non-BC contribution, and 2) a recently developed method based on the wavelength dependence of AAE (the “WDA method”), which indicated the existence of non-BC absorbers in 25.3% of the samples on average. We utilized trajectory and source area analyses and, in agreement with the results from other studies in this region, verified biomass burning emission sources, mainly to the northwest of the measurement site.

Highlights

Particulate black carbon (BC) and non-BC absorbers have several effects on the environment and human health
An aethalometer was employed in a 1-year campaign (November 2014–November 2015) in Nanjing, China, that aimed to estimate the contributions of black carbon (BC; annual average ± std = 4.0 ± 3.3 μg m–3) and non-BC absorbers, such as brown carbon, to the aerosol absorption coefficient
We applied two methods: 1) the traditional calculation from the aethalometer data, assuming an absorption Ångström exponent (AAE) of unity for BC (“AE method”), which provided an overall average of 27.2% for the non-BC contribution, and 2) a recently developed method based on the wavelength dependence of AAE, which indicated the existence of non-BC absorbers in 25.3% of the samples on average

Summary

Introduction

Particulate black carbon (BC) and non-BC absorbers have several effects on the environment and human health. They affect the atmosphere’s radiation balance both directly by absorbing incoming solar radiation (Bond et al, 2013) and indirectly and semi-directly by affecting the aerosols’ cloud properties (Brown et al, 2018; Allen et al, 2019). The BC and non-BC absorbers may have adverse health effects (Janssen et al, 2012). The non-BC absorbers, in turn, include 1) dust, 2) organics that are “dark” in color (humic-like substances, HULIS) and 3) light-absorbing organic matter called “brown carbon” (BrC). E.g., blown by wind from the soil into the atmosphere, whereas

Methods

Results

Conclusion