Intraurban NO₂ hotspot detection across multiple air quality products

Abstract

High-resolution air quality data products have the potential to help quantify inequitable environmental exposures over space and across time by enabling the identification of hotspots, or areas that consistently experience elevated pollution levels relative to their surroundings. However, when different high-resolution data products identify different hotspots, the spatial sparsity of “gold-standard” regulatory observations leaves researchers, regulators, and concerned citizens without a means to differentiate signal from noise. This study compares NO2 hotspots detected within the city of Chicago, IL, USA using three distinct high-resolution (1.3 km) air quality products: (1) an interpolated product from Microsoft Research’s Project Eclipse – a dense network of over 100 low-cost sensors; (2) a two-way coupled WRF-CMAQ simulation; and (3) a down-sampled product using TropOMI satellite instrument observations. We use the Getis-Ord Gi * statistic to identify hotspots of NO2 and stratify results into high-, medium-, and low-agreement hotspots, including one consensus hotspot detected in all three datasets. Interrogating medium- and low-agreement hotspots offers insights into dataset discrepancies, such as sensor placement and model physics considerations, data retrieval caveats, and the potential for missing emission inventories. When treated as complements rather than substitutes, our work demonstrates that novel air quality products can enable researchers to address discrepancies in data products and can help regulators evaluate confidence in policy-relevant insights.

Ethnoracial Disparities in Nitrogen Dioxide Pollution in the United States: Comparing Data Sets from Satellites, Models, and Monitors

“…Future characterizations of fine-scale NO 2 variations may further elucidate whether modeled or remotely sensed data are more accurate in their assessment of NO 2 levels. To this end, efforts to observe NO 2 at a high spatiotemporal resolution are underway through mobile monitoring, such as campaigns in San Francisco, CA, and surrounding areas, and dense urban monitoring networks, such as the dense network of sensors in Chicago, IL from Microsoft Research’s Project Eclipse . In the meantime, the spatially complete modeled and remotely sensed NO 2 data sets represent a leading, state-of-the-science means to surveil ambient NO 2 and analyze distributional effects and should be used more widely in tandem with surface-level monitors by researchers and regulators.…”