Air pollution persistent exceedance events in the Brazilian metropolis of Sao Paulo and associated surface weather patterns.

Air pollution is one of the main environmental problems in the metropolitan area of São Paulo (MASP) in Brazil, with frequent exceedances of air quality standards. Occasionally, the exceedance events last many days, resulting in continuous exposure to concentrations above the standards, with impacts to human health. In this air pollution long-term study, a method was developed to identify persistent exceedance events (PEE) of particulate matter (PM₁₀) and ozone (O₃) and associated surface weather patterns. Between 2005 and 2017, 119 PEE were identified, with exceedances occurring simultaneously in at least 50% of monitoring stations along 3 to 14 consecutive days. Median PM₁₀ and O₃ concentrations increased by 60% during the events. Mean fields of sea level pressure from global reanalysis data revealed the influence of high-pressure systems and pre-frontal conditions. PM₁₀ events were frequent in austral winter and mostly driven by anomalous atmospheric circulation with a wind change to northwest. On the other hand, O₃ events were common in the spring, associated with higher positive anomalies of temperature and solar radiation. Overall, results show that PEE span a regional scale, differing from ordinary exceedance events that can be driven by local conditions. Policy makers should be aware of the frequency of PEE in the development of mitigation measures against the exposure to harmful levels of air pollutants. The concept of PEE can be applied to other metropolitan areas and may support the development of data-driven air quality predictive models based on current or forecasted weather conditions. [ABSTRACT FROM AUTHOR]