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The Role of Ammonia in Atmospheric New Particle Formation and Aerosol Number Abundance at the Southern Great Plains Site
ARSHAD NAIR, Fangqun Yu, Gan Luo, The State University of New York at Albany
Abstract Number: 652
Working Group: Aerosol Chemistry
Abstract
New particle formation (NPF) and subsequent growth to cloud condensation nuclei (CCN) can contribute upwards of 50% of the global CCN budget. It is also a significant source of ultrafine aerosols with health implications. Ammonia (NH3) can play a significant role in determining NPF rates by its stabilizing effect on neutral and charged clusters. Understanding these processes are vital for air quality and climate. Here, we examine the role of NH3 in NPF and consequent effects on aerosol properties (number concentrations and their size distributions) during springtime 2018–2019 at the U.S. Department of Energy's (DOE) ARM Southern Great Plains (SGP) Central Facility located in Lamont, Oklahoma (36°36′18′′ N, 97°29′6′′ W; 318 m). We use the GEOS-Chem global 3-D atmospheric chemistry and transport model coupled with the size-resolved, multi-type, multi-component Advanced Particle Microphysics (APM) Model that incorporates the recently developed H2SO4–H2O–NH3 Ternary Ion-mediated Nucleation (TIMN) scheme, constrained with thermodynamic data from quantum-chemical calculations and Cosmics Leaving OUtdoor Droplets (CLOUD) measurements. For comparison with model simulations, we use the SGP observations of particle number size distributions (3–500 nm; TSI Model 3936 scanning mobility particle sizer (SMPS) and nanoSMPS), CN10 (condensation nuclei > 10 nm; TSI Model 3772 Condensation Particle Counter), CCN0.4 (CCN at 0.4% supersaturation; Droplet Measurement Technologies CCN-200), and aerosol composition speciation (SO4, NO3, NH4, Organics; Aerodyne ACSM). Inclusion of the effect of NH3 captures the occurrence of strong NPF and growth events and the magnitude and temporal variations of observed particle number concentrations. Simulated CN10 and CCN0.4 show improved agreement with observations (over a range of 4 orders of magnitude) with mean fractional bias reducing from −1.2 to −0.03 and −0.6 to −0.1, respectively. With the additional aid of submicron aerosol composition measurements and simulations, the role of NH3 in NPF and growth to potential cloud-forming particles is examined.