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Evidence of Organonitrate Formation at a High Altitude Site, Mahabaleshwar during Pre-monsoon Season

Category: Aerosol and Atmospheric Chemistry

Accepted Manuscripts
DOI: 10.4209/aaqr.2018.03.0110
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Vyoma Singla, Subrata Mukherjee , Govindan Pandithurai, Kundan K. Dani, Pramod D. Safai

  • Indian Institute of Tropical Meteorology, Pune 411 008, India

Highlights

Source apportionment of nitrate is done by sophisticated PMF technique.
Organo nitrate contributed 37.80 % to the total nitrate functionality.
NOx ratio for NIA factor was found to be 1.28.
NOx ratio of OOA-2 (~6.06) indicated isoprene oxidation as a major source of ON.


Abstract

The presence of organonitrate and organosulfate was identified at a high altitude site, Mahabaleshwar during the pre-monsoon of 2016. The Time of Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) was used to measure the organic and inorganic components of non-refractory particulate matter (NR-PM1) aerosol. Positive Matrix Factorization (PMF) was performed on the (i) organics mass spectra of aerosol (PMFOA) (ii) organics mass spectra merged with inorganics (PMFOA+IOA) and (iii) integrated mass spectra of organics with NO+ and NO2+ ions (PMFOA+NOx) to derive the chemical information on organonitrate and organosulfate. The results of PMFOA were used as a reference for validating the factors obtained through PMFOA+IOA and PMFOA+NOx results. The analysis of PMFOA resolved four PMF factors - hydrocarbon like OA (HOA), biomass burning like OA (BBOA), oxygenated OA-1 (OOA-1) and OOA-2. The analysis of PMFOA+IOA identified two additional inorganic factors - sulfate organic aerosol (OA) and nitrate OA. The factors-sulfate OA and nitrate OA contributed 36% and 6% respectively to the total aerosol mass. Although secondarily originated, the sulfate OA and nitrate OA displayed different diurnal profiles. The results of PMFOA+NOx were used for the quantification and apportionment of nitrate aerosol into two forms - organic nitrate and inorganic nitrate. Organic nitrate and inorganic nitrate contributed 38% and 62% respectively to the total nitrate aerosol mass. The diurnal variation of organic nitrate highlights photochemical oxidation as well as nocturnal oxidation by nitrate radical as the two major sources. This source apportionment study with combined (organic and inorganic) dataset provides new source factors and improves understanding about the sources and chemical nature of submicron aerosols in atmosphere. However, the quantification of organosulfate remains a limitation in this study.

Keywords

Tof-ACSM PMF Organonitrate Organosulfate NIA


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