Estimation of NO x and SO 2 emissions from Sarnia, Ontario, using a mobile MAX-DOAS (Multi-AXis Differential Optical Absorption Spectroscopy) and a NO x analyzer

• Published in: Atmospheric chemistry and physics Vol. 19; no. 22; pp. 13871 - 13889
• Main Authors: Davis, Zoe Y. W., Baray, Sabour, McLinden, Chris A., Khanbabakhani, Aida, Fujs, William, Csukat, Csilla, Debosz, Jerzy, McLaren, Robert
• Format: Journal Article
• Language: English
• Published: 19-11-2019
• ISSN: 1680-7324; 1680-7324
• DOI: 10.5194/acp-19-13871-2019

Sarnia, Ontario, experiences pollutant emissions
disproportionate to its relatively small size. The small size of the city
limits traditional top-down emission estimate techniques (e.g., satellite)
but a low-cost solution for emission monitoring is the mobile MAX-DOAS
(Multi-AXis Differential Optical Absorption Spectroscopy).
Measurements were made using this technique from 21 March 2017 to 23 March 2017
along various driving routes to retrieve vertical column densities (VCDs) of
NO2 and SO2 and to estimate emissions of NOx and SO2 from the Sarnia region. A novel aspect of the current study was the
installation of a NOx analyzer in the vehicle to allow real time
measurement and characterization of near-surface NOx∕NO2 ratios
across the urban plumes, allowing improved accuracy of NOx emission
estimates. Confidence in the use of near-surface-measured NOx∕NO2
ratios for estimation of NOx emissions was increased by relatively
well-mixed boundary layer conditions. These conditions were indicated by
similar temporal trends in NO2 VCDs and mixing ratios when measurements
were sufficiently distant from the sources. Leighton ratios within
transported plumes indicated peroxy radicals were likely disturbing the
NO–NO2–O3 photostationary state through VOC (volatile organic compound) oxidation. The average
lower-limit emission estimate of NOx from Sarnia was 1.60±0.34 t h−1 using local 10 m elevation wind-speed measurements. Our
estimates were larger than the downscaled annual 2017 NPRI-reported (National Pollution Release Inventory)
industrial emissions of 0.9 t NOx h−1. Our lower-limit
estimate of SO2 emissions from Sarnia was 1.81±0.83 t SO2 h−1, equal within uncertainty to the 2017 NPRI downscaled
value of 1.85 t SO2 h−1. Satellite-derived NO2 VCDs
over Sarnia from the ozone monitoring instrument (OMI) were lower than
mobile MAX-DOAS VCDs, likely due to the large pixel size relative to the
city's size. The results of this study support the utility of the
mobile MAX-DOAS method for estimating NOx and SO2 emissions in
relatively small, highly industrialized regions, especially when supplemented
with mobile NOx measurements.