- 1Pacific Northwest National Laboratory, Richland, WA, USA (manishkumar.shrivastava@pnnl.gov)
- 2State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, China
- 3Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA
- 4Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC, USA
- 5Department of Environmental Toxicology, University of California, Davis, CA, USA
- 6State Key Joint Laboratory of Environmental Simulation and Pollution Control, BIC-ESAT and IJRC, College of Environmental Sciences and Engineering, Peking University, Beijing, China
- 7Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah
- 8Department of Physics, Michigan Technological University, Houghton, MI 49931
In forested regions around the world, biogenic emissions have been reported to be key drivers of new particle formation (NPF) that contribute to about half the budget of global cloud condensation nuclei (CCN). However, over the central U.S., far from forests and influenced by croplands and urban emissions, the processes driving NPF and CCN are not well understood. Using detailed regional model simulations using WRF-Chem, we show that acid-base reactions including sulfuric acid and dimethyl amines (DMA) are key nucleation drivers at the SGP site during two simulated days in the springtime. We also show that anthropogenic extremely low volatility organics (ELVOCs) formed by the oxidation of anthropogenic VOCs in the atmosphere are critical for explaining the observed particle growth. Conversely, simulated non-NPF days at SGP are characterized by low-level clouds, which reduce photochemical activity, sulfuric acid, and ELVOC concentrations, thereby explaining the lack of NPF. At the Bankhead National Forest (BNF) site the southeastern U.S., we show that nucleation rates are limited by availability of sulfuric acid in this forested area. Our study highlights the large potential heterogeneities in nucleation and particle growth mechanisms between forested and urban/farmland-influenced areas that need to be verified with new BNF measurements.
Additionally, we simulate droplet-resolved cloud chemistry and the interactions between turbulence and cloud chemistry using a one-dimensional explicit mixing parcel model (EMPM-Chem) to simulate how isoprene epoxydiol secondary organic aerosol (IEPOX-SOA) formation evolves in individual cloud droplets within rising cloudy parcels in the atmosphere. We find that as subsaturated air is entrained into and turbulently mixed with the cloud parcel, cloud droplet evaporation causes a reduction in droplet sizes, which leads to corresponding increases in per droplet ionic strength and acidity. Increased droplet acidity in turn greatly accelerates the kinetics of IEPOX-SOA formation. Our results provide key insights into single-cloud-droplet chemistry, suggesting that entrainment mixing may be an important process that increases SOA formation in the real atmosphere.
How to cite: Shrivastava, M., Zhang, J., Zaveri, R., Zhao, B., Pierce, J., O' Donnell, S., Fast, J., Gaudet, B., Shilling, J., Zelenyuk, A., Murphy, B., Pye, H., Zhang, Q., Trousdell, J., Chen, Q., Krueger, S., Shaw, R., and Ovchinnikov, M.: Processes governing new particle formation over croplands and urban influenced central USA and effects of entrainment mixing on cloud chemistry and formation of secondary organic aerosols, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3830, https://doi.org/10.5194/egusphere-egu25-3830, 2025.
