Anthropogenic Photolabile Chlorine in the Cold-Climate City of Montreal

Abstract

Chlorine atoms play a key role in the oxidative potential of the atmosphere and biogeochemical cycling of selected elements. This study provides a decadal analysis (2010−2019) of chloride ions in PM2.5 particles in the city of Montreal, where these are most concentrated systematically in the winter (up to 1.6 µg/m3). We also herein present the measurement of photolabile chlorine, which includes chlorine-containing compounds (e.g., Cl2, HOCl, ClNO2, ClNO3, and BrCl) that release chlorine atoms upon interaction with radiation, in urban Montreal, Canada using Cl2-RPGE (Cl2 Reactive Phase Gas Extraction) tubes and quantifying the chlorinated product by GC-MS. Photolabile chlorine in urban Montreal was measured during a discontinuous period primarily in summer 2018 and winter 2019 with a time resolution of 30 min, with concentrations ranging from 3 to 545 ng/m3 expressed as Cl2. The reported values are considered lower limits, as compounds such as HOCl and ClNO2 can only be partially converted in the current setup. The largest peak of gaseous photolabile chlorine occurred in the winter, when significant sources of anthropogenic salt are used in snow removal in the city. This coincides with observed chloride ion measurements in airborne particles, implying that anthropogenic salt addition produces photoactive chlorine. The maximum chlorine signal was consistently obtained during the daytime, which is in accordance with the tropospheric radiation profile. Complementary photochemistry laboratory experiments indicated that upon tropospheric radiation (340 ≤ λ ≤ 400 nm; UVA), an increase (20–100%) was observed, confirming the formation of Cl atoms from photolabile chlorine compounds. Thus, this portable technique is adequate for Cl atoms and photolabile chlorine-containing compounds upon photolysis using UVA lamps. High-resolution S/TEM and energy-dispersive X-ray spectroscopy (EDS) were used to evaluate collected particle morphology and composition. The behavior of complementary pollutants (O3, CO, PM2.5, and NOx) was also briefly discussed. We herein discuss the measurement of photolabile halogens within a northern urban metropolitan environment and the impact of anthropogenic sources on chlorine concentrations.

Black Carbon Particles Physicochemical Real‐Time Data Set in a Cold City: Trends of Fall‐Winter BC Accumulation and COVID‐19

“…Aerosol composition is diverse, originating from natural and anthropogenic sources such as organic, inorganic (including metallic), and biological particles (Bond et al., 2013 ; Hall et al., 2020 ; IPCC, 2013 ; Rahim et al., 2019 ; Rangel‐Alvarado et al., 2015 ; Rivas et al., 2020 ). Airborne black carbon (BC) is a type of aerosol that formed as by‐product of incomplete combustion of fossil fuel, accounting for 5%–15% of the annual urban particulate matter concentration (Xu et al., 2020 ; Yang et al., 2011 ).…”

“…Snow organic compounds have been shown to undergo physicochemical processes including re‐emission to air, upon melting (Nazarenko et al., 2016 , 2017 ). Halogenated salts are commonly added as a de‐icing agent in snowy cities, affecting the oxidation potential of the lower atmosphere (Hall et al., 2020 ; Pal et al., 2020 ; Rahim et al., 2019 ; Rangel‐Alvarado et al., 2019 ).…”

Interaction of Air Pollution with Snow and Seasonality Effects

“…Field observation, laboratory-experimental, and modeling studies are included, along with environmental monitoring and source apportionment research of local, regional, or global relevance. The fieldwork covered in the articles was conducted in various types of locations: urban sites (e.g., the cities of Chengdu, Gucheng [1], Helsinki [2], Montreal [3], and Moscow [4]); small cities and rural areas (e.g., Yulin, Huimin, and Zhengzhou [1], Tien Shan [5], Valday [6], and "36 sites on a 2800 km submeridional profile from the city of Barnaul to Salekhard" [7]); industrial [6]; remote (e.g., the Arctic, Antarctic [8], and Tibetan Plateau [9]); and other locations (e.g., along highways [10] and in the mountains [11]).…”

“…The articles collected in this Special Issue focus on the following aspects of the interaction of air pollution with snow and the effects of seasonality: (1) the impact of deposited air pollutants on the snow albedo [2,11,12], (2) the composition and properties of particulate and volatile air pollutants detected in snow [4,7,8,11], (3) links with the sources and impact assessment, including, more specifically, seasonality of black carbon in the air and snow [1,2,5,9,12], (4) metals and metalloids in snow [4,6], (5) radioactive isotopes in snow [10], (6) snowpack pollution as an indicator of atmospheric pollution [1,[6][7][8]10,12], (7) photochemistry of compounds released due to interactions with anthropogenic particles that became mixed with snow [3], and (8) the effect of snow on greenhouse gas fluxes from the underlying peat [13].…”

“…Hall and colleagues [3] explored the source and seasonality of photolabile chlorine species (e.g., Cl 2 , HOCl, ClNO 2 , ClNO 3 , and BrCl) and the impact of salt application during snow removal operations on the presence of photolabile chlorine species in the ambient air. They examined the association of the photolabile chlorine species in the ambient air with the abundance of chloride ions in PM 2.5 particles based on a decadal analysis (2010-2019) in the city of Montreal.…”