The Potential for Chlorine Activation in Continental Environments and from Urban Grime Surfaces
EMMA MCLAY, Yao Yan Huang, D. James Donaldson, Trevor VandenBoer, York University
Abstract Number: 180
Working Group: Aerosol Chemistry
Abstract
Atmospheric chlorine radicals can play a role in atmospheric oxidation pathways that may lead to ozone and secondary organic aerosol (SOA) production. Their importance derives from their reaction rates which exceed those of hydroxyl radicals by 1-2 orders of magnitude. Nitryl chloride (ClNO2), a well-known precursor to chlorine radicals, is largely understood to come from heterogeneous reaction of chloride-containing surfaces with N2O5, but these are predominantly limited to aerosols with sea-salt influence, despite the observed presence of ClNO2 in continental areas free of sea-salt aerosol. This work aims to understand heterogeneous ClNO2 chemistry in continental areas and on non-aerosol surfaces, like urban grime, the chemically complex films found on impervious urban surfaces.
Analysis of publicly available particulate matter ionic composition data from Canadian continental locations (Etobicoke, Saskatoon, Quebec, and Montreal) revealed ubiquitous depletion of chloride with correlation of nitrate and the sodium-chloride difference (‘missing chloride’). This implies displacement of chloride by nitrate through some mechanism, which is enhanced during wintertime when road salts are applied. Similarly, in a study of urban grime samples from three continental locations in Ontario, evidence for such displacement was also found, but only for one location (Toronto) and with reversed seasonality. This prior work inspired a concerted field campaign in February 2024 in Toronto where urban grime and size-resolved aerosol samples were collected simultaneously, targeting road salt influence, in addition to summertime collection of size-resolved aerosols for comparison. Ionic composition of both sample types will be determined and compared. Direct reaction of N2O5 with the urban grime samples in a coated-wall flow tube reactor will be conducted to probe any ClNO2 production. This presentation will explore Cl-reservoirs and ClNO2 production from aerosol and non-aerosol surfaces in environments that are currently lacking study, providing additional insight into broader chlorine chemistry that can contribute to atmospheric oxidation.