publications

2025

1. 

   Impacts of Interannual Isoprene Variations on Methane Lifetimes and Trends

   James (Young Suk) Yoon, Kelley C. Wells, Dylan B. Millet, and 3 more authors

   Geophysical Research Letters, 2025

   Abs DOI

   Recent observations show anomalously high methane growth in 2020, which has been attributed to increased wetland emissions and decreased OH from lower COVID-19 nitrogen oxide (NOx) emissions. NOx is not the only species that affects OH—isoprene, the most significant non-methane hydrocarbon by total emissions, is oxidized by OH, which can deplete OH during periods of high emissions. Using satellite isoprene retrievals from the Cross-track infrared sounder (CrIS), we find anomalously high isoprene columns during 2020, coincident with high methane growth. Isoprene’s oxidation produces carbon monoxide, which can be transported over longer distances and decrease OH outside of isoprene source regions. Elevated isoprene concentrations may have contributed 13% (bounds: 10%–28%) of 2020’s methane growth if we assume no change in NOx emissions in 2020. Since COVID-19 decreased anthropogenic NOx emissions, this estimate is an upper-limit and may depend on whether isoprene or NO emissions drove this isoprene anomaly.

2024

1. 

   Sensitive Response of Atmospheric Oxidative Capacity to the Uncertainty in the Emissions of Nitric Oxide (NO) From Soils in Amazonia

   Ben H. Lee, J. William Munger, Steven C. Wofsy, and 5 more authors

   Geophys. Res. Lett, 2024

   Abs DOI

   Soils are a major source of nitrogen oxides, which in the atmosphere help govern its oxidative capacity. Thus the response of soil nitric oxide (NO) emissions to forcings such as warming or forest loss has a meaningful impact on global atmospheric chemistry. We find that the soil emission rate of NO in Amazonia from a common inventory is biased low by at least an order of magnitude in comparison to tower-based observations. Accounting for this regional bias decreases the modeled global methane lifetime by 1.4%–2.6%. In comparison, a fully deforested Amazonia, representing a 37% decrease in global emissions of isoprene, decreases methane lifetime by at most 4.6%, highlighting the sensitive response of oxidation rates to changes in emissions of NO compared to those of terpenes. Our results demonstrate that improving our understanding of soil NO emissions will yield a more accurate representation of atmospheric oxidative capacity.