The Impact of COVID-19 Lockdown Strategies on Oxidative Properties of Ambient PM10 in the Metropolitan Area of Milan, Italy

Abstract

This research investigates the impact of controlling pandemic measures on the characteristics of atmospheric particulate matter (PM), with specific concern to its toxicity, measured by its oxidative properties. The investigated PM10 samples were collected in the metropolitan area of Milan during the epidemic lockdown, and their oxidative potential (OP) was assessed using ascorbic acid (AA) and dithiothreitol (DTT) acellular assays. During the full lockdown, we estimated reductions to 46% and 60% for nitrogen dioxide (NO2) and black carbon (BC) concentrations, respectively, based on the aggregated 2018–2019 data of NO2 and BC levels, used as baseline conditions. To quantify the impact of lockdown restrictions on PM oxidative activity, we studied the OP data measured in our laboratory on PM10 filters and directly compared the results from 15–30 April 2020 with those from the same time span in 2019. The OPAA values dropped to nearly 50%, similar to the concentration decrease in Elemental Carbon (EC) and traffic related metals, as well as to the variation in NO2 level. Otherwise, the OPDTT responses decreased to nearly 75%, as described by the corresponding reduction in Organic Carbon (OC) concentration and BC level.

Impact of COVID-19 lockdown on particulate matter oxidative potential at urban backgroundversustraffic sites

“…In fact, this last study suggests unchanged contributions from the biomass burning and secondary aerosols. Interestingly, this is also consistent with the findings in an urban background site in Milan, Italy highlighting that OP (also assessed by DTT assay) has been mostly impacted by biomass burning resulting to weaker reductions than other pollutants during the lockdown period (33). Meanwhile, in a typical coal-combustion city in Linfen, China, a significant decrease in OP was observed attributed to the decrease of several subgroups of primary organic aerosols (OA) (32).…”

“…Interestingly, this is also consistent with the ndings in an urban background site in Milan, Italy highlighting that OP (also assessed by DTT assay) has been mostly impacted by biomass burning resulting in weaker reductions than other pollutants during the lockdown period. 33 Meanwhile, in a typical coalcombustion city in Linfen, China, a signicant decrease in OP was observed attributed to the decrease of several subgroups of primary organic aerosols (OA). 32 These authors also found an enhanced formation of secondary OA resulting from high oxidation capacity (i.e., high O 3 levels) in the atmosphere during the lockdown period.…”

“…At an urban background site in the metropolitan area of Milan, Italy, the OP of PM 2.5 (particularly OP assessed by DTT assay) was only slightly reduced during the lockdown period with much lower change than the other air quality parameters (e.g., chemical species in PM 2.5 , NO 2 , and BC). 33,34 Overall, the lockdown periods opened a unique opportunity to evaluate OP of PM as a health exposurerelevant metric, especially in areas where no signicant reduction in PM levels took place during the lockdown periods.…”

“…, chemical species in PM 2.5 , NO 2 , and BC). 33,34 Overall, the lockdown periods opened a unique opportunity to evaluate OP of PM as a health exposure-relevant metric, especially in areas where no significant reduction in PM levels took place during the lockdown periods.…”

Seasonal and Spatial Variations of the Oxidative Properties of Ambient PM2.5 in the Po Valley, Italy, before and during COVID-19 Lockdown Restrictions

“…Although the influence of the epidemic restrictions on the air quality has been described in a great number of papers [1][2][3][4][5][6][7][8][9][18][19][20][21][22][23][24], to our knowledge, the impact on aerosol toxicity has been reported only in a few papers [2,6,22,23]. Therefore, the main goal of this work was to investigate the influence of quarantine lockdown on the oxidative toxicity and chemical composition of PM 2.5 particles to understand the change of PM properties before and during the pandemic shutdown.…”