Carbonaceous Aerosols in the Eastern Indo- Gangetic Plain: Tracers, transport and sources

Singh, Shruti (2019) Carbonaceous Aerosols in the Eastern Indo- Gangetic Plain: Tracers, transport and sources. Masters thesis, Indian Institute of Science Education and research Kolkata.

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Abstract

Carbonaceous aerosols can be classified into two types: organic carbon (OC) and elemental carbon (EC). OC can either be directly emitted as particles and hence termed as primary organic carbon (POC) or produced from oxidation of gaseous organic precursors, followed by condensation on pre-existing aerosols, termed as secondary organic carbon (SOC). EC on the other hand is emitted during combustion process such as vehicle exhaust and crop burning. OC is a mixture of several organic compounds that can be classified as aromatic and aliphatic. OC has negative radiative forcing effect on the climate as it scatters away the solar radiation. EC on the other hand has a positive climate forcing influence as it absorbs the solar radiation. EC particles are also chemically inert; they do not react in the atmosphere under normal conditions and have adverse effects on human health and also influences the climate system. Several studies have been done worldwide on source identification and seasonal distribution of carbonaceous aerosols. There are few studies in India in the Indo-Gangetic Plain that anchors on field measurement of carbonaceous aerosols. But we do not have seasonal information regarding the sources, chemical composition and concentrations of PM₂.₅. Similar work in the eastern part of India is quite limited. Thus, in order to understand the source of PM₂.₅ particles in the eastern IGP we have planned this project. In this study, we have tried to understand the distribution, seasonalities and sources of fine mode aerosol OC and EC at a rural site downwind of intense open biomass burning and residential fuel use emissions. We are also trying to look at the effectiveness of traditional indicators (OC/EC, char-EC/soot-EC, nss-K⁺/EC and nss-SO₄²⁻ /EC). For this purpose we have used low-volume samplers for PM₂.₅ collection, followed by analysis of OC and EC using a thermal- optical analyzer with charring correction and TOC analyzer for WSOC concentrations. The major findings from our study were that in our study site there is significant SOC formation both in summer and post monsoon season. The SOC in summer is associated with WIOC which is comprised of OC3, PC and OC4 thermal factions. On the other hand, SOC in post monsoon comprises of both WSOC and WIOC which consists of OC1, OC2, OC3 and PC thermal fractions. We also found out that Char- EC/Soot-EC is a better tracer for biomass burning than other traditional indicators.

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