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

Abstract

Abstract. 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.

NOx Emission Flux Measurements with Multiple Mobile-DOAS Instruments in Beijing

“…These diverse sensitivities were caused by traffic flow and traffic jam. This study adds to the existing literature on this topic expanding upon the work of previous studies [22][23][24][25][26][27][28][29][30][31][32][34][35][36]. Our work also indicates that wind information is crucial, as having the actual time and height resolved wind measurements yields great advantages for measuring mega-cities' emission flux.…”

“…The wind field uncertainty is the main error source of mobile-DOAS emission flux measurements [27]. Several studies on mobile-DOAS indicate that having a wind profile is crucial for mobile-DOAS [18,22,24,26,31]. A near real-time measurement of the wind field is recommended for calculating the emission flux [18,26,31].…”

“…This platform can be a car or an airplane [18][19][20][21][22]; here, we focus on cars. Mobile-DOAS has been widely used for emission flux measurements and has achieved good results [23][24][25][26][27][28][29][30][31][32]. Previous studies have aimed at point sources [25,26] or area emitting [27][28][29][30][31][32] measurements taken from stationary emission sources.…”

“…Previous studies have aimed at point sources [25,26] or area emitting [27][28][29][30][31][32] measurements taken from stationary emission sources. Some studies have also used mobile-DOAS to examine CHIMERE chemistry transport model (CTM) outputs or emission inventories [26,31]. Improvements in the mobile-DOAS measurements quality has been highly requested by the scientific community to enhance the capabilities needed to determine NOx emission fluxes particularly in Chinese mega-cities.…”

Validation of MAX-DOAS retrievals of aerosol extinction, SO<sub>2</sub>, and NO<sub>2</sub> through comparison with lidar, sun photometer, active DOAS, and aircraft measurements in the Athabasca oil sands region

“…Tropospheric VCDs of NO 2 were determined from the Pandora total column VCDs by subtracting stratospheric VCDs modelled using the PRATMO stratospheric photochemical box model (McLinden, 2000). PRATMO was used as described in , except monthly mean OSIRIS ozone profiles (Degenstein et al, 2009) and MODIS surface reflectivities (McLinden et al, 2014) were employed. The Pandora SO 2 VCDs presented are assumed to be representative of tropospheric SO 2 VCDs since stratospheric SO 2 was assumed to be negligible.…”