28 Apr 2023
 | 28 Apr 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Examining the vertical heterogeneity of aerosols over the Southern Great Plains

Yang Wang, Chanakya Bagya Ramesh, Scott Giangrande, Jerome Fast, Xianda Gong, Jiaoshi Zhang, Alyssa Matthews, Fan Mei, Ahmet Tolga Odabasi, John Shilling, Jason Tomlinson, Die Wang, and Jian Wang

Abstract. Atmospheric aerosols affect the global energy budget by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). Both aerosol direct and indirect effects are affected by the vertical distribution of aerosols in the atmosphere, which is further influenced by a range of processes, such as aerosol dynamics, long-range transport, and entrainment. However, many observations of these processes are based on ground measurements, limiting our ability to understand the vertical distribution of aerosols and simulate their impact on clouds and climate. In this work, we examined the vertical heterogeneity of aerosols over the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) using data collected from the Holistic Interactions of Shallow Clouds, Aerosols and Land Ecosystems (HI-SCALE) campaign. The vertical profiles of meteorological and aerosol physiochemical properties up to 2500 m above the ground are examined based on the 38 flights conducted during the HI-SCALE campaign.

The aerosol properties over the SGP show strong vertical heterogeneity and seasonal variabilities. The aerosol concentrations at the surface are the highest due to strong sources of emission at ground level. The mode diameter of these aerosols during summer (~ 100 nm) is larger than that during spring (~ 30 nm), potentially as a result of enhanced condensational growth due to enriched volatile organic compounds in summer. The concentration of aerosols below 30 nm in the boundary layer (BL) (e.g., below 1000 m) during spring is higher than that during summer, a result of the stronger new particle formation (NPF) events and a reduced condensation sink in spring. In the BL, the size of the aerosols gradually increases with altitude due to condensational growth and cloud processing. However, the composition of the aerosols remained similar, with organics and sulfates representing 59.8 ± 2.2 % and 22.7 ± 2.1 % of the total mass in the BL. Through the vertical profiles of aerosol properties, we noticed a considerable number of NPF events (7 out of 38) in the upper BL, where the newly formed particles continue to grow as they are mixed down to the surface. There is also an indication that deep convection brings aerosols from the free troposphere (FT) to the surface, where they grow to contribute to the cloud condensation nuclei (CCN). Overall, the vertical heterogeneity of aerosols over the SGP is influenced by aerosol dynamics (new particle formation, growth, and cloud processing) and transport processes (long-range transport, entrainment, and convective downward transport). Case studies showing the influence of these factors are discussed.

Yang Wang et al.

Status: open (until 06 Jul 2023)

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Yang Wang et al.


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Short summary
We report the vertical profiles of aerosol properties over the Southern Great Plains (SGP), a region influenced by shallow convective clouds, land-atmosphere interactions, boundary layer turbulence, and the aerosol life cycle. We examined the processes that drive the aerosol population and distribution in the lower troposphere over the SGP. This study helps improve our understanding of aerosol-cloud interactions and the model representation of aerosol processes.