Low Molecular Weight Monocarboxylic Acids in PM2.5 and PM10: Quantification, Seasonal Variation and Source Apportionment

Nidhi Verma,K Maharaj Kumari,Anita Lakhani,Aparna Satsangi

doi:10.4209/aaqr.2016.05.0183

Nidhi Verma, K Maharaj Kumari + Show 2 more

Open Access

https://doi.org/10.4209/aaqr.2016.05.0183

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Abstract

ABSTRACTPM2.5 and PM10 aerosols from a semi-urban site of Agra (27°10′N, 78°05′E) in North-Central India were analyzed for carbonaceous aerosols (Organic and Elemental carbon), low molecular weight monocarboxylic acids (Acetic and Formic acid) along with inorganic ions (Cl–, NO3–, SO42–, K+ and Ca2+) during April 2014 to August 2015. The average PM2.5 and PM10 mass concentrations were 86.3 ± 71.3 and 169.7 ± 100.5 µg m–3, respectively; about 45% of PM2.5 and 67% of PM10 samples were above NAAQ (National Ambient Air Quality) standards. The average organic carbon (OC) and elemental carbon (EC) concentrations were 18.2 ± 12.3 and 6.7 ± 4.5 µg m–3, respectively in PM2.5 and 25.2 ± 14.1 and 8.1 ± 5.9 µg m–3 respectively in PM10. The average concentration of acetic acid (AA) in PM2.5 and PM10 were 330 ± 211 and 392 ± 224 ng m–3 respectively. The average concentration of formic acid (FA) in PM2.5 and PM10 were 348 ± 193 and 336 ± 175 ng m–3 respectively. Formic acid concentration was higher in PM2.5 than PM10 but the difference is not statistically significant. Both AA and FA showed similar seasonal variation: winter > post-monsoon > summer > monsoon. Low temperature and high relative humidity in winter season favours gas to particle conversion resulting in high concentrations. The average FA to AA (F/A) ratio was 0.69 indicating dominance of primary sources at the study site. Correlation analysis of AA and FA with major ions (Cl–, NO3–, SO42–, K+ and Ca2+), EC, secondary organic carbon and trace gases (O3 and CO) was performed to identify their primary or secondary origin. The results of correlation analysis suggest that AA is mainly contributed by primary sources while FA originates from secondary sources.

Highlights

Ambient aerosol particles consist of both organic and inorganic constituents, and play an important role in global climate change, precipitation, visibility, cloud microphysical properties, and human health problems (Menon et al, 2002; Huebert et al, 2003)
The back trajectories were simulated in each season using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model based on the GDAS Meteorological Data (Draxler and Rolph, 2003) (Fig. S1, supplementary information)
Trajectories were dominantly localized in nature and the increase in local emission sources like burning of coal or wood to combat cold may result in high levels of both PM2.5 and PM10

Summary

Introduction

Ambient aerosol particles consist of both organic and inorganic constituents, and play an important role in global climate change, precipitation, visibility, cloud microphysical properties, and human health problems (Menon et al, 2002; Huebert et al, 2003). Carbonaceous aerosols are a major component of atmospheric particulate matter, contributing up to 10–70% of particulate mass (Tsapakis et al, 2002). A substantial fraction of carbonaceous aerosols consist of water soluble organic compounds (WSOCs) which account for up to 70% of the total aerosol mass (Sorooshian et al, 2007; Jung et al, 2010). WSOCs consist of a complex mixture of organic species and are ubiquitous in the atmosphere (Kanakidou et al, 2005). Carboxylic acids represent major fraction of organic

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