Elsevier

Journal of Aerosol Science

Volume 56, February 2013, Pages 53-60
Journal of Aerosol Science

Mass size distribution of carbon in atmospheric humic-like substances and water soluble organic carbon for an urban environment

https://doi.org/10.1016/j.jaerosci.2012.06.006Get rights and content

Abstract

Aerosol samples were collected with a micro-orifice uniform deposit impactor in an aerodynamic diameter (AD) range of 0.5–10 μm in central Budapest, Hungary for 12 days. Aqueous aerosol extracts and atmospheric humic-like substances (HULIS) were obtained from the combined aerosol samples for each impactor stage. Water-soluble organic carbon (WSOC) and carbon in HULIS (HULIS-C) were measured in the samples with a total organic carbon analyzer. The analytical data were inverted into semi-smooth mass size distributions, and modal parameters were derived. The size distributions for both WSOC and HULIS-C consisted of three peaks: a coarse mode and two accumulation submodes. The geometric mean AD for the coarse mode was 6.4 μm for both WSOC and HULIS-C. Contribution of the coarse mode to the total concentration of WSOC and HULIS-C were substantial and similar for both components, i.e., approximately 20%. The splitting of the accumulation mode into condensation and droplet submodes was explained by water processing of aerosol particles in the air. The geometric mean ADs of the condensation submode for the WSOC and HULIS-C were 0.37 and 0.31 μm, respectively, and the droplet submode appeared at 1.72 and 1.22 μm, respectively. The condensation submode was larger than the droplet submode by similar ratios of 1.7–1.8 for both WSOC and HULIS-C. The relative concentrations of the two submodes were likely influenced by local meteorology, in particular by relative humidity, pollutant gases, and water uptake properties and aging of fine particles.

Highlights

► Mass size distributions of WSOC and HULIS-C are trimodal. ► Condensation and droplet submodes, and coarse mode are identified. ► 80% of total WSOC and HULIS-C concentrations are associated with fine particles. ► Relative concentrations of the submodes likely depend on the environment. ► Contributions of the coarse mode to WSOC and HULIS-C concentrations are important.

Section snippets

Introduction and objectives

Water-soluble chemical compounds including both inorganic and organic constituents in fine-sized atmospheric aerosol particles play an important role in the biogeochemical cycling of water and other substances (Ramanathan et al., 2001, Mahowald, 2011), climate (Facchini, Mircea, Fuzzi, & Charlson, 1999), and several other environmental processes (Fuzzi et al., 2006). The effects of inorganic salts are well documented, while the organic compounds still represent a challenge. This is caused by

Collection of aerosol samples

An aerosol sample collection and measurement campaign was conducted in central Budapest (5, Rákóczi Street, latitude 47°29’37” N, longitude 19°03’38” E, altitude 111 m above the mean sea level) at a kerbside site within a street canyon from 23 April through 5 May 2002 (Salma et al., 2001, Salma et al., 2010). Mean traffic flow of motor vehicles in both directions at the site (obtained from loop counting) over the campaign was 2.0×103 h−1. The samplings and measurements were performed at a height

Mass size distribution of WSOC

The mass size distribution of WSOC obtained from the combined impactor stages is shown in Fig. 1. It represents the average size distribution for 12 days. The distribution consists of three modes. The coarse mode has a GMAD of 6.4 μm, and its concentration represents 21% of the total WSOC concentration. This relative contribution is considerable. The WSOC-containing coarse particles are usually associated with mechanical disintegration processes such as soil erosion and dispersion, and

Conclusions

The mass size distributions of WSOC and water-soluble HULIS-C for an urban environment in springtime contained three modes. About 80% of both the WSOC and HULIS-C concentrations were apportioned to fine particles. The accumulation mode was split into two submodes due to water processing, similarly for major ionic constituents. Abundances of the submodes likely depend on ambient RHs, water uptake properties and age of particles, and on pollutant gases. Therefore, the extent of the environmental

Acknowledgements

Financial support by the Hungarian Scientific Research Fund (contract K84091) and the Belgian Federal Science Policy Office is appreciated. The authors are indebted to J. Cafmeyer of Ghent University for collection of the aerosol samples, and L. Jurecska of the Eötvös University for assistance in the TOC measurements.

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