Carbon Monoxide Emissions from the Washington, DC, and Baltimore Metropolitan Area: Recent Trend and COVID-19 Anomaly

We analyze airborne measurements of atmospheric CO concentration from 70 flights conducted over six years (2015-2020) using an inverse model to quantify the CO emissions from the Washington, DC, and Baltimore metropolitan areas. We found that CO emissions have been declining in the area at a rate of approximate to-4.5 % a(-1) since 2015 or approximate to-3.1 % a(-1) since 2016. In addition, we found that CO emissions show a Sunday effect, with emissions being lower, on average, than for the rest of the week and that the seasonal cycle is no larger than 16 %. Our results also show that the trend derived from the NEI agrees well with the observed trend, but that NEI daytime-adjusted emissions are approximate to 50 % larger than our estimated emissions. In 2020, measurements collected during the shutdown in activity related to the COVID-19 pandemic indicate a significant drop in CO emissions of 16 % relative to the expected emissions trend from the previous years, or 23 % relative to the mean of 2016 to February 2020. Our results also indicate a larger reduction in April than in May. Last, we show that this reduction in CO emissions was driven mainly by a reduction in traffic.

Automated summary

We analyzed airborne measurements of atmospheric CO concentration over a six-year period (2015-2020) and used an inverse model to quantify CO emissions in the Washington, DC, and Baltimore metropolitan areas. Our findings show a decline in CO emissions at a rate of approximately -4.5% per year since 2015 or approximately -3.1% per year since 2016. We also observed a Sunday effect in CO emissions, with lower levels compared to the rest of the week, and a seasonal cycle with no significant variation. The study reveals that the NEI daytime-adjusted emissions are approximately 50% higher than the estimated emissions. Furthermore, during the COVID-19 pandemic, there was a significant reduction in CO emissions, particularly due to decreased traffic.