Abstract
Particulate 2-methyltetrols (2-MT) and 2-methylglyceric acid (2-MG) are typically used to indicate the abundance of isoprene-derived secondary organic aerosols (SOA). However, their formation and fate are not fully understood. In this study, we showed that particulate 2-MT and 2-MG collected at multiple monitoring sites under a wide range of atmospheric and emission conditions, with concentrations spanning six orders of magnitudes, are well reproduced with an expanded isoprene-SOA scheme implemented into the Community Multiscale Air Quality (CMAQ) model. The scheme considers their three-phase (gas-aqueous-organic phase) partitioning, formation from acid-driven multiphase reactions, and degradation by OH radicals in the gas and aqueous phases. The model results reveal that a non-aqueous formation pathway or direct biogenic emission is needed to supplement the commonly assumed acid-driven multiphase reaction process to explain the observed 2-MT concentrations. This missing pathway contributes to 20–40% of 2-MT in areas with aerosol pH<2 and more than 70% under less acidic conditions (pH~2–5), such as those encountered in the western US and China. The typical summertime gas-phase photochemical lifetimes of 2-MT and 2-MG are estimated to be 4–6 and 20–30 h, respectively, and their aqueous lifetimes are approximately 20–40 h. Our simulations show that predicted 2-MT is mainly influenced by its aqueous phase loss to OH, but 2-MG is more sensitive to gas phase OH loss due to the preferential partitioning of the two tracers in the aqueous and gas phases, respectively.
| Original language | English |
|---|---|
| Article number | 69 |
| Number of pages | 8 |
| Journal | npj Climate and Atmospheric Science |
| Volume | 6 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 17 Jun 2023 |
Bibliographical note
© The Author(s) 2023Funding Information:
The authors would like to thank the Texas A&M High Performance Research Computing ( https://hprc.tamu.edu/ ) for providing the computing resources essential for completing the project. M. Shrivastava and J.Z. acknowledge support from the United States Department of Energy (DOE) Office of Science, Office of Biological and Environmental Research (BER) through the Early Career Program at the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the DOE by Battelle Memorial Institute under contract DE-AC06-76RL01830. J.L., T.Z., and M.Z. acknowledge funding from the National Natural Science Foundation of China (NSFC, Grant NO. 42030708). X.D. acknowledges funding from the National Natural Science Foundation of China (NSFC, Grant NO. 42177090). J.Z.Y. acknowledges funding from the National Natural Science Foundation of China (NSFC, Grant NO. 21177031 and NO. 91543130). G.I.VW. acknowledges funding from the United States National Science Foundation Graduate Research Fellowship (#DGE 1106400). SV-TAG data from the SOAS field campaign was collected and analyzed by G.I.VW., L.D.Y., and A.H.G., supported by the United States National Science Foundation Atmospheric Chemistry Program (#1250569 and 1243354). The instrument as deployed was developed through support from the United States Department of Energy (DOE) SBIR grant DE-SC0004698. E.A.S. acknowledges funding from the United States Environmental Protection Agency (EPA STAR grant no. 83540101).