Turbulent Flux Measurements of the Near‐Surface and Residual‐Layer Small Particle Events. Issue 17 (9th September 2022)

• Record Type: Journal Article
• Authors: Islam, M. M.; Meskhidze, N.; Rasheeda Satheesh, A.; Petters, M. D.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 17(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-09
• Subjects: 0305 -- 3307 -- 3322 -- 0322; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD036289
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: According to recent field studies, almost half of the New Particle Formation (NPF) events occur aloft, in a residual layer, near the top of the boundary layer. Therefore, measurements of the meteorological parameters, precursor gas concentrations, and aerosol loadings conducted at the ground level are often not representative of the conditions where the NPFs take place. This paper presents new measurements obtained during the Turbulent Flux Measurements of the Residual Layer Nucleation Particles, conducted at the Southern Great Plains research site. Vertical turbulent fluxes of 3–10 nm‐sized particles were measured using a sonic anemometer and two condensation particle counters with nominal cutoff diameters of ≥ $\ge $ 3 nm and ≥ $\ge $ 10 nm mounted at the top of the 10‐m telescoping tower. Aerosol number size distribution (5–300 nm) was determined through the ground‐based Scanning Mobility Particle Sizers. The size selected (15–50 nm) particle hygroscopicity was derived with the Humidified Tandem Differential Mobility Analyzer. The ground level observations were supplemented by vertically‐resolved measurements of horizontal and vertical wind speeds and aerosol backscatter. The data analysis suggests that (a) turbulent flux measurements of 3–10 nm particles can distinguish between near‐surface and residual‐layer small particle events; (b) sub‐50 nm particles had a hygroscopicity value of 0.2, suggesting that organic compounds dominate atmospheric nanoparticle chemical composition at the site; and (c) current methodologies are inadequate for estimating the dry deposition velocity of sub‐10 nm particles because it is not feasible to measure particle concentration very near the surface, in the diffusion sublayer. Plain Language Summary: The atmosphere is filled with microscopic particles, termed "aerosols." Many of these particles are produced through a complex process known as new particle formation or nucleation. As the particle concentration in the atmosphere has been shown to influence Earth's radiative balance and human health, the formation of new particles from the gas phase is a topic of interest for both climate and air quality sciences. Researchers have identified some factors that influence nucleation events, though none of these factors can explain and predict nucleation consistently. There is evidence that roughly half of the nucleation events detected at ground level originate above the surface, where the process is favored by colder temperatures, lower preexisting particle concentrations, and higher relative humidity. Therefore, ground level measurements may not always be representative of the conditions under which nucleation takes place. The inability to distinguish between ground level and elevated nucleation events is contributing to inconsistencies in our understanding of the factors that influence nucleation. Here, we show that vertical turbulent fluxes of 3–10 nm‐sized particles can be used to distinguish between near‐surface and residual‐layer nucleation. We also show that the existing methodology is inadequate for the estimation of particle dry deposition velocity. We believe these findings will help to better represent aerosols in regional and global climate models. Key Points: Near‐surface/residual‐layer particle nucleation events can be identified by positive/negative turbulent fluxes of 3–10 nm sized particles Hygroscopic diameter growth factor measurements show that organics are dominating sub‐50 nm composition at the Southern Great Plains site The eddy‐covariance measurements are inadequate for the estimation of sub‐10 nm particle deposition velocity in most environments