Organic contaminants are widespread in the atmosphere, and atmospheric deposition transfers contamination to aquatic environments, including environmentally sensitive coastal regions. Given the large number of organic contaminants and diverse contaminant sources, we aim to map the distribution of these contaminants in the atmosphere by identifying potentially universal spatial patterns of various organic vapors and associating these patterns with different types of sources. To achieve this, we established two large passive air sampler (PAS) networks in the St. Lawrence Estuary region in Quebec (QC) and the Salish Sea region in British Columbia (BC) in Canada. The PAS networks include 169 passive air samples across 118 unique sites of various source types between 2019 and 2022. The PAS extracts were analyzed for 353 organic substances including polychlorinated biphenyls (PCBs), polycyclic aromatic compounds (PACs), organochlorine pesticides (OCPs), halogenated methoxy benzenes (HMBs), industrial organochlorine and metabolic transformation products of pesticides, halogenated flame retardants (HFRs), organophosphate esters (OPEs), and neutral poly- and perfluorinated substances (nPFAS). The obtained extensive dataset was subject to hierarchical clustering to reveal spatial patterns of organic contaminants in the atmosphere and the observed patterns were associated with different types of sources. Specifically, we observed four archetypes of spatial concentration variability across Canada. "Point Source" signatures are characterized by elevated concentration in the vicinity of major release locations. PACs are the compound group that exhibit this pattern. For example, PAC hotspots were observed near fuel-related facilities such as fuel storage depots and oil refineries, as well as combustion sources like waste incinerators, fuel combustion on railways, and metal industries. A “Population” signature applies to compounds whose air concentrations are highly correlated with population density and is associated with emissions from consumer products. This cluster of compounds includes HFRs, fluorotelomer alcohols, OPEs and PCB-11. This “Population” pattern appears to be universal, evidenced by the correlations between concentration and population density observed in this study could be extrapolated to other regions. The “Water Source” signature applies to substances with elevated levels in the vicinity of water bodies, from which they evaporate. Compounds belonging to this cluster include α-hexachlorocyclohexane (α-HCH) and HMBs. Another group of compounds, i.e., hexachlorobutadiene, hexachlorobenzene and pentachlorobenzene, displays a “Uniform” signature, indicative of a lack of major sources within the study area. These chemicals are typically volatile and have long atmospheric half-lives, which facilitate their dispersion in the atmosphere.
 

Organic Contaminant Sources,Spatial Patterns,Coastal Regions