Monitoring polycyclic aromatic hydrocarbons deposition in eastern Canada using moss biomonitoring: A large-scale study of spatial patterns and environmental influences.

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants released into the atmosphere from both natural and anthropogenic sources. This study presents the first large-scale spatial assessment of atmospheric PAHs across Quebec, Canada, using passive biomonitoring with Pleurozium schreberi moss. PAH analysis was conducted using high-performance liquid chromatography with fluorescence detection (HPLC-FLD), targeting 10 PAHs for spatial biomonitoring and 15 PAHs to assess the impacts of the 2023 wildfire events. Over 200 samples were collected primarily from southern Quebec, the most populated region with major urban and industrial centers, as well as from remote northern regions to capture background deposition levels. Despite the influence of intense regional wildfires and transboundary air masses, PAH concentrations across most of Quebec remained low, highlighting the province relatively clean atmospheric conditions. Elevated PAH levels were largely confined to the St. Lawrence Urban Corridor and corresponded with local industrial and urban activity, as well as potentially prevailing winds from the U.S. The intense wildfire events of 2023 did not increase total PAH loads in the tested sites but led to marked compositional shifts, with diagnostic ratios indicating amplified contributions from pyrogenic sources. These findings reinforce the effectiveness of moss biomonitoring for detecting both regional pollution gradients and temporal shifts in source signatures, while establishing a valuable baseline for future atmospheric studies in eastern North America.