Carbonaceous aerosols

Optical properties of biomass burning organic aerosols from laboratory measurements

As a consequence of increasing global temperatures, wildfires have started to increase in severity and the resulting biomass burning particulate emissions have had a significant impact on human health and visibility. Prior knowledge of the optical properties of the aerosols from these wildfires is required to accurately estimate the emission concentrations using satellites.

In my work, I have studied the artifacts associated with traditional techniques used to measure the optical properties of light-absorbing organic aerosol—also termed brown carbon. My work indicates that organic emissions which have low water-solubility and high light absorption efficiencies are primarily co-emitted with black carbon during high-temperature combustion.

Articles associated with this work:

Shetty, N. J., Pandey, A., Baker, S., Hao, W. M., & Chakrabarty, R. K. (2019). Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods. Atmospheric Chemistry and Physics, 19(13), 8817-8830. (link)

Shetty, N., Beeler, P., Paik, T., Brechtel, F. J., & Chakrabarty, R. K. (2021). Bias in quantification of light absorption enhancement of black carbon aerosol coated with low-volatility brown carbon. Aerosol Science and Technology, 55(5), 539-551. (link)

Pandey, A., Shetty, N. J., & Chakrabarty, R. K. (2019). Aerosol light absorption from optical measurements of PTFE membrane filter samples: sensitivity analysis of optical depth measures. Atmospheric Measurement Techniques, 12(2), 1365-1373. (link)

Optico-chemical characterization of organic aerosols from real-world wildfires

Field studies confirm findings from laboratory measurements and provide new insights into mechanisms that might be overlooked in controlled settings. I participated in the 2019 NASA/NOAA Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign.

During this field campaign, we characterized the change in organic aerosol optical properties with atmospheric processing, chemical composition, and, fire combustion conditions. We found that organic aerosols have increased light absorption after exposure to nitrate radicals (associated with nighttime chemistry). We also discovered a class of highly absorbing organic aerosol particles which could be the dominant light-absorbing constituent of wildfire emissions. We also confirmed the presence of organics which had low water-solubility and were co-emitted with black carbon.

Articles associated with this work:

Shetty, N., Liu, P., Liang, Y., Sumlin, B., Daube, C., Herndon, S., ... & Chakrabarty, R. K. (2023). Brown carbon absorptivity in fresh wildfire smoke: associations with volatility and chemical compound groups. Environmental Science: Atmospheres, 3(9), 1262-1271. (link)

Chakrabarty, R. K., Shetty, N. J., Thind, A. S., Beeler, P., Sumlin, B. J., Zhang, C., ... & Mishra, R. (2023). Shortwave absorption by wildfire smoke dominated by dark brown carbon. Nature Geoscience, 16(8), 683-688. (link)

Sumlin, B., Fortner, E., Lambe, A., Shetty, N. J., Daube, C., Liu, P., ... & Chakrabarty, R. K. (2021). Diel cycle impacts on the chemical and light absorption properties of organic carbon aerosol from wildfires in the western United States. Atmospheric Chemistry and Physics, 21(15), 11843-11856. (link)

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