New Insights Into the Role of Atmospheric Transport and Mixing on Column and Surface Concentrations of NO<sub>2</sub> at a Coastal Urban Site
Taylor J. Adams, Jeffrey A. Geddes, Elena Lind
Abstract
Abstract We use a multi‐year record of Pandora‐derived NO 2 total column abundance in Boston to examine the influence of atmospheric transport on column NO 2 and its surface concentrations during the warm season in a coastal urban environment. We derive tropospheric NO 2 estimates from the total column with a measurement‐model fusion approach using near‐real‐time estimates of stratospheric NO 2 from NASA's Goddard Earth Observing System Composition Forecast model system and find the average influence of stratospheric NO 2 at this urban site can be 30%–70% depending on season and time of day. Sea breeze days tend to exhibit rapid temporal variability in the column that which can go in the opposite direction of changes in surface NO 2 concentrations. By comparing tropospheric NO 2 with surface concentrations, we constrain the role of boundary layer entrainment processes in the evolution of surface NO 2 concentrations, while highlighting the value of column measurements in identifying sea breeze frontal dynamics. We estimate an apparent equal mixing layer height of NO 2 and infer that surface NO x emissions remain concentrated near the surface regardless of atmospheric stability regime. When comparing the Pandora‐ to TROPOMI‐derived column NO 2 measurements, we find that sea breeze days present a unique challenge likely due to higher spatial heterogeneity in NO 2 and the meteorology involved that is not well represented in retrieval inputs. Our observations provide new insights into column and surface variability of NO 2 which will be relevant to interpreting geostationary observations, especially in coastal urban locations.