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Investigating Urban Air Quality Using Surface NO2 Derived from Column Measurements


Atmospheric trace gases near the Earth’s surface can have important human and environmental health impacts. In particular, the trace gas nitrogen dioxide (NO2), which is commonly emitted by traffic, biomass burning, and industrial sources, can be a major threat to human respiratory health, leading to increased rates of asthma, lung cancer, and overall mortality. In the Greater Toronto Area (GTA) and in the Detroit-Windsor Area (DWA), NO2 and other trace gases are being monitored by ground-based Pandora UV-visible spectrometers that are part of the Pandonia Global Network. We present NO2 surface volume mixing ratios derived from Pandora direct sun total column measurements to monitor air quality using the conversion method from Zhao et al. (2019). Their method uses three inputs in addition to the Pandora total columns: the stratospheric NO2 column from the Ozone Monitoring Instrument (OMI), the free troposphere NO2 column from the GEOS-Chem chemical transport model, and the ratio of NO2 surface volume mixing ratio to planetary boundary layer column from Environment and Climate Change Canada’s regional air quality forecast model, Global Environmental Multi-scale-Modelling Air quality and Chemistry (GEM-MACH). The derived estimates of surface NO2 are compared with in situ measurements, and their level of agreement is tested for dependence on meteorological conditions, including wind speed and direction, temperature, and surface pressure. This presentation will provide an overview of this column-to-surface conversion method, a summary of preliminary results for each site in the GTA and in the DWA, and an outline of plans toward using this approach to improve and validate satellite estimates of surface NO2.

Zhao, X., et al., Retrieval of total column and surface NO2 from Pandora zenith-sky measurements, Atmos. Chem. Phys., 19, 10619–10642,, 2019.

Host: Aleksandra Elias Chereque
Event series  Brewer-Wilson Seminar Series