Quantifying and attributing methane (CH4) and carbon monoxide (CO) emission changesin New York City during the COVID-19 shutdown

Abstract:

In response to the COVID-19 pandemic, New York ordered state-wide closures of all non-essential businesses in March 2020. On-road transportation and economic activity were dramatically reduced in the New York City metro area. Fortuitously, we began measuring carbon gas concentrations (including CH4 and CO) at an observatory in Manhattan in January 2020, which continued throughout the lockdown and into summer 2020. This study presents analysis of the observed changes in the atmospheric composition of New York City for CH4 and CO and discusses the possible causes of these changes. Measured concentrations indicate a clear decline in both CH4 and CO between February and April. To investigate emission changes, we separate the concentration variations from meteorological impacts using footprint analysis techniques with HRRR-STILT. This analysis shows much of the concentration change may be driven by meteorology, with strong winds clearing the metro area throughout late March and early April. We isolate the remaining concentration changes and attribute them to emissions sectors using various baseline emission inventories (e.g., EDGAR, EPA, FIVE) for both CH4 and CO. Our results indicate an unexpectedly large drop in the proportion of local CH4 emissions, the source of which is undetermined. We also confirm the expected reduction in CO emissions from on-road transportation.