Study of secondary organic aerosol formation and aging using ambient air in an oxidation flow reactor during high pollution events over Delhi

Vikas Goel; Nidhi Tripathi; Mansi Gupta; Lokesh Kumar Sahu; Vikram Singh; Mayank Kumar

doi:10.1016/j.envres.2024.118542

Study of secondary organic aerosol formation and aging using ambient air in an oxidation flow reactor during high pollution events over Delhi

Environ Res. 2024 Feb 23;251(Pt 1):118542. doi: 10.1016/j.envres.2024.118542. Online ahead of print.

Authors

Vikas Goel¹, Nidhi Tripathi², Mansi Gupta³, Lokesh Kumar Sahu⁴, Vikram Singh⁵, Mayank Kumar⁶

Affiliations

¹ School of Interdisciplinary Research, Indian Institute of Technology Delhi, Delhi, 110016, India; Department of Mechanical Engineering, Indian Institute of Technology Delhi, Delhi, 110016, India. Electronic address: vikasgoel1002@gmail.com.
² Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, 55128, Germany; Physical Research Laboratory, Navrangpura, Ahmedabad, 380009, India.
³ Physical Research Laboratory, Navrangpura, Ahmedabad, 380009, India; Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar, 382355, India.
⁴ Physical Research Laboratory, Navrangpura, Ahmedabad, 380009, India.
⁵ Department of Chemical Engineering, Indian Institute of Technology Delhi, Delhi, 110016, India.
⁶ Department of Mechanical Engineering, Indian Institute of Technology Delhi, Delhi, 110016, India. Electronic address: kmayank@iitd.ac.in.

PMID: 38403149
DOI: 10.1016/j.envres.2024.118542

Abstract

Secondary aerosols constitute a significant fraction of atmospheric aerosols, yet our understanding of their formation mechanism and fate is very limited. In this work, the secondary organic aerosol (SOA) formation and aging of ambient air of Delhi are studied using a potential aerosol mass (PAM) reactor, an oxidation flow reactor (OFR), coupled with aerosol chemical speciation monitor (ACSM), proton transfer reaction time of flight mass spectrometer (PTR-ToF-MS), and scanning mobility particle sizer with counter (SMPS + C). The setup mimics atmospheric aging of up to several days with the generation of OH radicals. Variations in primary volatile organic compounds (VOCs) and oxygenated volatile organic compounds (OVOCs) as a function of photochemical age were investigated. Primary VOCs such as benzene, toluene, xylene, trimethyl benzene, etc. decrease and OVOCs like formic acid, formaldehyde, acetone, ethanol, etc. increase substantially upon oxidation in OFR. The highest organic aerosol (OA) enhancement was observed for the 4.2 equivalent photochemical days of aging i.e., 1.84 times the ambient concentration, and net OA loss was observed at very high OH exposure, typically after 8.4 days of photochemical aging due to heterogeneous oxidation followed by fragmentation/evaporation. In ambient air, OA enhancement is highest during nighttime due to the high concentrations of precursor VOCs in the atmosphere. SMPS + C results demonstrated substantial new particle formation upon aging and decrement in preexisting aerosol mass. This is the first experimental study conducting an in-situ evaluation of potential SOA mass generated from the ambient aerosols in India.

Keywords: Ambient air; Multigenerational oxidation; New particle formation; Oxidation flow reactor; Secondary organic formation.