Figure 9.

Twenty-four hour total STILT surface influence contours for total column NO₂ exceedances on 23 April (a, d), 25 April (b, e), and 9 October (f–k) and a low NO₂ case on 16 April 2020 (c), for comparison. Contour lines represent surface influence of 1ppb (μmolm⁻² s⁻¹)⁻¹ and are colored by hour-of-day of the receptor. October 9 is overlaid with EDGAR inventories of NO_x for 2015 (kgNO_x m⁻² yr⁻¹). The area encircled by each contour indicates the region of emissions that reaches the Manhattan and Queens observation sites for a given time and day.