Atmospheric trace metals in particulate matter (PM) pose significant environmental and health risks, making their study crucial for understanding urban air quality. These metals originate from various sources, including traffic emissions, industrial activities, and natural processes, and can have detrimental effects on human health and ecosystems. Investigating their concentrations and sources provides valuable insights into pollution dynamics and informs mitigation strategies. In this study, PM10 trace metal concentrations were investigated at an urban background site in Manchester, assessing the influence of different sources including the effect of the COVID-19 lockdown. Utilizing an Xact 625i ambient metal analyzer and applying Positive Matrix Factorization (PMF), four sources of PM10 metals were identified: vehicle nonexhaust emissions (NEE), biomass burning, sea salt, and construction dust. The study used Multiple Linear Regression to quantify the contributions of the factors’ time series to the variations in concentrations of PM1, PM2.5, and PM10 measured using a FIDAS. Surprisingly, while the sea salt, construction dust, and biomass burning all made appreciable contributions to the variances of the expected size fraction, the NEE contribution was small, implying that its influence on measured PM concentrations was low. This may be because the particles were large and were not transported efficiently away from the nearby roads. Analysis also showed decreases in concentrations of NEE, NOx, and optical absorption from traffic measured by an aethalometer (Babs 950 (traffic)) during lockdown by 37, 66, and 41%, respectively. While a decrease associated with a reduction in traffic is expected, the disparity between the different metrics may be due to the average speed of vehicles increasing, changing the emission factors.
Bibi et al. (Tue,) studied this question.