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PM 2.5 was sampled over a seven-year period (2013–2019) at two locations ∼50 km apart in Southern Ontario (concurrently for five years: 2015–2019). One is a heavily industrialized site (Hamilton), while the other was a rural site (Simcoe). To assess the impact of industrialization on the composition and sources of PM affecting air quality in these two locations, positive matrix factorization coupled with dispersion normalization (DN-PMF) was used to identify six and eight factors at Simcoe and Hamilton, respectively. The Simcoe factors in order of diminishing PM mass contribution were: particulate sulphate (pSO4), secondary organic aerosol (SOA), crustal matter, particulate nitrate (pNO3), biomass burning, and vehicular emissions. At Hamilton, the effects of industrialization were observed by the ∼36% higher average ambient PM 2.5 concentration for the study period as well as the presence of factors unique to metallurgy, i.e., coking and steelmaking, compared to Simcoe. The coking and steelmaking factors contributed ∼15% to the PM mass at Hamilton. Seasonal variants of appropriate nonparametric trend tests with the associated slopes (Sen's) were used to assess statistically significant changes in the factor contributions to PM 2.5 over time. Specifically at Hamilton, a significant decline in PM contributions was noted for coking (−0.03 μg/m³/yr or −4.1%/yr) while steelmaking showed no statistically significant decline over the study period. Other factors at Hamilton that showed statistically significant declines over the study period were: pSO4 (−0.27 μg/m³/yr or −12.6%/yr), biomass burning (−0.05 μg/m³/yr or −9.02%/yr), crustal matter (−0.03 μg/m³/yr or −5.28%/yr). These factors mainly accounted for the significant decline in PM 2.5 over the study period (−0.35 μg/m³/yr or −4.24%/yr). This work shows the importance of long-term monitoring in assessing the unique contributions and temporal changes of industrialization on air quality in Ontario and similarly affected locations. [Display omitted] • DN-PMF applied to 24-hr integrated PM 2.5 data from 2 close locations in Ontario. • 8 factors found in Hamilton, a heavily industrialized city, 6 the same as at Simcoe. • Coking & steelmaking factors were additionally found in Hamilton but not at Simcoe. • Trends tests showed significant declines in particulate sulphate at both locations. • In Hamilton, industrial factors had most PM 2.5 heavy metals and elemental species. [ABSTRACT FROM AUTHOR]

Increased nitrate (NO3) concentrations in streamwaters draining forested catchments are reportedly an early indicator of nitrogen (N) saturation. Nitrate concentrations in streams draining 16 forested catchments in south central Ontario were monitored over a 16-year period, during which time N bulk deposition was relatively constant (∼9 kg ha-1 yr-1). Mean annual NO3 concentrations in streams were both highly variable among catchments and among years, although patterns of annual concentration were similar among many catchments. Coherence analysis identified two stream groupings. Shallow soils, moderate slopes, low NO3 concentration, and a large wetland component characterized the first group. The second group had primarily upland characteristics including deeper soils, steeper slopes, higher NO3 concentrations, and a much smaller wetland component. Patterns in NO3 concentration in wetland-influenced streams appeared to be related to summer drought and cumulative frost depth, whereas NO3 concentrations in upland-draining streams appeared to be related to both mean annual air temperature and summer drought Because a number of different climate parameters as well as the physical character of the catchments apparently influence NO3 export, NO3 concentrations in streams are not a good indicator of N saturation in this region. [ABSTRACT FROM AUTHOR]