A multi-scale analysis of urban air quality

Air quality remains a serious threat to urban residents; it is the primary contributor to respiratory illnesses. Those living in densely populated neighborhoods are particularly vulnerable. Despite considerable advancements in our overall understanding of urban air pollution, our insights into neighborhood- and street-level pollution remain insufficient. Dense urban neighborhoods are dominated by tall buildings and high levels of traffic, leading to complex flow patterns and uneven distribution of primary pollutants. Herein, we delve into the street and neighborhood-scale pollution dynamics in New York City, harnessing both mobile and in-situ observations. We used a backpack fitted with research-grade instruments to monitor particulate matter (PM2.5) and ozone in the summer of 2023. Between July and August, nearly 50 runs were conducted, sampling multiple neighborhoods during various time periods. In-situation observations from multiple public air quality networks were also included in our analysis. Our results show a high degree of uniformity in street-level ozone concentration in NYC, while the particulate matter concentration varied significantly. On days impacted by synoptic disturbances, both ozone and particulate matter concentrations were nearly uniform throughout the city. The fixed ground stations were able to adequately capture the median PM2.5 concentration. However, they missed the extremes, which were, in some cases, two to five times the median value. The observations were also used to validate an urbanized WRF-Chem model and satellite-derived measurements. The numerical simulations conducted at 4km X 4km resolution performed better than the current forecast model in predicting both PM2.5 and ozone concentration.