Comment on egusphere-2025-6080
Year: 2026
Type: peer-review
Abstract: . Particulate nitrate (NO3−) is a key target for controlling air pollution, yet its response to NOx abatement remains uncertain in cold climates. This study assesses trends of fine- and coarse-mode NO3− (f-NO3− and c-NO3−) during 1990–2019 in seven Canadian cities, making use of the long-term data collected by the National Air Pollution Surveillance (NAPS) network, and revealed disproportionate trends between NO3− and NOx emissions across Canada. In Edmonton, annual mean f-NO3− decreased by ~60 % from 2007–2019 while provincial NOx emissions declined by only 10–20 %; comparable patterns were also observed in five out of the six other cities in the most recent decade. Such disproportionate trends were diagnosed to be caused by reduced primary f-NO3− emissions, localized dispersion, and Arctic Oscillation–modulated wind anomalies. Conversely, all cities exhibited a transient f-NO3− increase during 1998–2007, coincident with early NOx controls and consistent with unintended enhancement of primary emissions of f-NO3− formed within stationary-combustion plumes. c-NO3− was largely insensitive to NOx reduction in most cities (except Edmonton), with its trends governed by neutralization reactions with alkaline aerosols rather than HNO3 availability. These findings can help interpret the weak or absent f-NO3− response to NOx reductions worldwide, especially in cold-climate regions.
Authors: Fan, Qinchu, Yao, Xiaohong, Zhang, Leiming
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
OpenAlex ID: W7117994635
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