Quantifying burning efficiency in megacities using the NO₂∕CO ratio from the Tropospheric Monitoring Instrument (TROPOMI)

Abstract

Abstract. This study investigates the use of co-located nitrogen dioxide (NO2) and carbon monoxide (CO) retrievals from the TROPOMI satellite to improve the quantification of burning efficiency and emission factors (EFs) over the megacities of Tehran, Mexico City, Cairo, Riyadh, Lahore, and Los Angeles. Efficient combustion is characterized by high NOx (NO+NO2) and low CO emissions, making the NO2∕CO ratio a useful proxy for combustion efficiency (CE). The local enhancement of CO and NO2 above megacities is well captured by TROPOMI at short averaging times compared with previous satellite missions. In this study, the upwind background and plume rotation methods are used to investigate the accuracy of satellite-derived ΔNO2∕ΔCO ratios. The column enhancement ratios derived using these two methods vary by 5 % to 20 % across the selected megacities. TROPOMI-derived column enhancement ratios are compared with emission ratios from the EDGAR v4.3.2 (Emission Database for Global Atmospheric Research v4.3.2) and the MACCity (Monitoring Atmospheric Chemistry and Climate and CityZen) 2018 emission inventories. TROPOMI correlates strongly (r=0.85 and 0.7) with EDGAR and MACCity, showing the highest emission ratio for Riyadh and lowest emission ratio for Lahore. However, inventory-derived emission ratios are 60 % to 85 % higher than TROPOMI column enhancement ratios across the six megacities. The short lifetime of NO2 and the different vertical sensitivity of TROPOMI NO2 and CO explain most of this difference. We present a method to translate TROPOMI-retrieved column enhancement ratios into corresponding emission ratios, thereby accounting for these influences. Except for Los Angeles and Lahore, TROPOMI-derived emission ratios are close (within 10 % to 25 %) to MACCity values. For EDGAR, however, emission ratios are ∼65 % higher for Cairo and 35 % higher for Riyadh. For Los Angeles, EDGAR and MACCity are a factor of 2 and 3 higher than TROPOMI respectively. The air quality monitoring networks in Los Angeles and Mexico City are used to validate the use of TROPOMI. For Mexico City and Los Angeles, these measurements are consistent with TROPOMI-derived emission ratios, demonstrating the potential of TROPOMI with respect to monitoring burning efficiency.

TROPOMI NO2 in the United States: A Detailed Look at the Annual Averages, Weekly Cycles, Effects of Temperature, and Correlation With Surface NO2 Concentrations

“…In an additional step, NO X emissions can be computed by combining the satellite data with meteorological information (Beirle, Borger, et al, 2019, Beirle, Boersma, et al, 2011Goldberg, Lu, Streets, et al, 2019;Goldberg, Saide, et al, 2019;Lorente, Boersma, et al, 2019;Lu et al, 2015;Valin et al, 2013) or by combining the satellite data with chemical transport models (Canty et al, 2015;Cooper, Martin, Padmanabhan, & Henze, 2017;Elissavet Koukouli et al, 2018;Mijling & Van Der A, 2012;Qu et al, 2017;Souri et al, 2016). Due to the consistency and robustness of the remotely sensed NO 2 data record, scientists are beginning to infer information from the NO 2 data about other trace gases such as CO 2 (Goldberg, Lu, Oda, et al, 2019;Konovalov et al, 2016;Reuter et al, 2019), CH 4 (de Gouw et al, 2020), and CO (Lama et al, 2020), since remotely sensed measurements of those trace gases are generally less reliable. Therefore, remotely sensed NO 2 can also be helpful in indirectly estimating greenhouse gas emissions.…”

Impacts of the COVID-19 Lockdown Measures on the 2020 Columnar and Surface Air Pollution Parameters over South-Eastern Italy

“…The results on the significance of the differences between different periods are shown in Table S4. Figure 9c illustrates the Pre-LD, LD, and Post-LD box plots of the NO 2 /CO ratio, because this parameter was generally used to determine the relative contributions from combustion sources and road traffic (e.g., [61,62]). We found a significant increase in the mean values of the NO 2 /CO ratio in Post-LD period with respect to the corresponding values in Pre-LD and LD periods.…”

Towards sector-based attribution using intra-city variations in satellite-based emission ratios between CO2 and CO

“…Analyzing remotely-sensed NO x plumes with relatively short lifetime can help identify local fossil fuel CO 2 (FFCO 2 ) sources that would otherwise be difficult (Reuter et al, 2019;Fujinawa et al, 2021). While at the same time, such reactivity raises the requirement of accurately accounting for chemical transformation and complicates the interpretation of emission signals or ERs from NO x observations (Lama et al, 2020;Hakkarainen et al, 2021).…”

“…To our knowledge, only a few global inventories, such as the Emissions Database for Global Atmospheric Research (EDGAR, Solazzo et al, 2021), offer global anthropogenic CO and CO 2 emissions. Considering the challenge in approximating ERs, the knowledge derived from observations may 1) complement inventory-based ERs (e.g., CO:NO x ratio in Lama et al, 2020) and 2) facilitate the emission constraint for a desired species, usually with relatively large uncertainties (Wunch et al, 2009;Palmer et al, 2006;Wang et al, 2009;Brioude et al, 2012;Nathan et al, 2018). Such prior success motivates us to derive ERs from satellite observations of multiple tracers.…”