Aerosol-methane interaction

Mineral dust and sea salt aerosols can interact through iron-catalyzed chlorine chemistry, releasing reactive chlorine that affects the global methane budget. This is my current postdoctoral research at Cornell University.

Chlorine radicals oxidize methane 10–16 times faster than hydroxyl radicals, but they also destroy ozone, reducing hydroxyl formation, which is the dominant methane sink. These competing effects make it difficult to determine the net impact of chlorine chemistry on methane removal and, ultimately, climate.

Recent studies have shown that iron in mineral dust can catalyze chlorine production from sea salt aerosols, a process that could be significant over ocean regions where dust and sea salt mix, but whose efficiency remains uncertain. Methane oxidation by chlorine produces CO that is depleted in 13C due to kinetic isotope effects, a signature that has been used to detect chlorine-methane reactions. However, uncertainties in the isotopic signatures of other CO sources complicate efforts to isolate the contribution of this pathway to the global methane budget.

We are working to disentangle these effects using models at multiple scales, validated against laboratory measurements and field observations, to better constrain the climate implications of iron-catalyzed chlorine chemistry.

Research Goals

• Implement iron-catalyzed chlorine chemistry in CESM with the soluble iron process
• Quantify the impact on global methane lifetime
• Validate model results using CO and δ¹³C-CO isotopic observations
• Validate iron-catalyzed chlorine radical production rates using lab and field aerosol observations

Related Publications

1. Yao, Y., Mahowald, N., Hess, P., Meidan, D., and Mak, J. . Global assessment of iron-catalyzed chlorine production and its impact on the atmospheric methane budget, to be submitted for Journal of Geophysical Research: Atmospheres
2. Yao, Y., Natalie M. Mahowald, Peter Hess, John E. Mak, B Gaubert, Process-Based CO isotope constraints on iron-catalyzed chlorine contributions to the methane sink, in prep.