Multiple new-particle growth pathways observed at the US DOE Southern Great Plains field site

Abstract

Abstract. New-particle formation (NPF) is a significant source of aerosol particles into the atmosphere. However, these particles are initially too small to have climatic importance and must grow, primarily through net uptake of low-volatility species, from diameters ∼ 1 to 30–100 nm in order to potentially impact climate. There are currently uncertainties in the physical and chemical processes associated with the growth of these freshly formed particles that lead to uncertainties in aerosol-climate modeling. Four main pathways for new-particle growth have been identified: condensation of sulfuric-acid vapor (and associated bases when available), condensation of organic vapors, uptake of organic acids through acid–base chemistry in the particle phase, and accretion of organic molecules in the particle phase to create a lower-volatility compound that then contributes to the aerosol mass. The relative importance of each pathway is uncertain and is the focus of this work. The 2013 New Particle Formation Study (NPFS) measurement campaign took place at the DOE Southern Great Plains (SGP) facility in Lamont, Oklahoma, during spring 2013. Measured gas- and particle-phase compositions during these new-particle growth events suggest three distinct growth pathways: (1) growth by primarily organics, (2) growth by primarily sulfuric acid and ammonia, and (3) growth by primarily sulfuric acid and associated bases and organics. To supplement the measurements, we used the particle growth model MABNAG (Model for Acid–Base chemistry in NAnoparticle Growth) to gain further insight into the growth processes on these 3 days at SGP. MABNAG simulates growth from (1) sulfuric-acid condensation (and subsequent salt formation with ammonia or amines), (2) near-irreversible condensation from nonreactive extremely low-volatility organic compounds (ELVOCs), and (3) organic-acid condensation and subsequent salt formation with ammonia or amines. MABNAG is able to corroborate the observed differing growth pathways, while also predicting that ELVOCs contribute more to growth than organic salt formation. However, most MABNAG model simulations tend to underpredict the observed growth rates between 10 and 20 nm in diameter; this underprediction may come from neglecting the contributions to growth from semi-to-low-volatility species or accretion reactions. Our results suggest that in addition to sulfuric acid, ELVOCs are also very important for growth in this rural setting. We discuss the limitations of our study that arise from not accounting for semi- and low-volatility organics, as well as nitrogen-containing species beyond ammonia and amines in the model. Quantitatively understanding the overall budget, evolution, and thermodynamic properties of lower-volatility organics in the atmosphere will be essential for improving global aerosol models.

Analysis of a Multi-Year Record of Size-Resolved Hygroscopicity Measurements from a Rural Site in the U.S.

“…Air arriving from the south often has elevated sulfur dioxide (SO 2 ) originating from electricity production, industrial facilities, and fuel combustion, and nitrogen oxides (NO x = NO + NO 2 ) from industrial facilities and vehicle emissions. Air arriving from the north commonly brings SOA precursors (Hodshire et al, 2016), and lower (than with southerly winds) concentrations of NO x . The county-wise emission densities of SO 2 and NO x are shown in Tables S1-S2, and Fig.…”

Errors in nanoparticle growth rates inferred from measurements in chemically reacting aerosol systems

“…The aerosol general dynamic equation (GDE) (Friedlander, 2000;Seinfeld, 1979, 1980) describes the time rate of change of size-dependent particle concentration and composition by such processes. Recent work has focused on understanding processes that affect growth rates (GRs) of freshly nucleated atmospheric nanoparticles (Smith et al, 2008(Smith et al, , 2010Riipinen et al, 2012;Hodshire et al, 2016;Kontkanen et al, 2016;Tröstl et al, 2016). This is important because a particle's survival probability increases with GRs (McMurry and Friedlander, 1979;Weber et al, 1997;Kerminen and Kulmala, 2002;Kuang et al, 2010).…”

Temperature-Dependent Diffusion of H2SO4 in Air at Atmospherically Relevant Conditions: Laboratory Measurements Using Laminar Flow Technique

“…To confirm the reproducibility of the experimental data the H 2 SO 4 concentration at any arbitrary distance along the flow tube was measured again. Moreover, the reproducibility was checked by exchanging the flow tube parts, so that the part with 4 holes was moved up, and H 2 SO 4 …”

“…Particulate matter contributes to air pollution and acts as seeds for cloud droplets, thus affecting cloud properties and radiation budget.Gaseous sulfuric acid H 2 SO 4 , formed via oxidation of SO 2 by OH radicals, is the most important driver of new particle formation in the present-day atmosphere, and the concentration of H 2 SO 4 vapour has a significant impact on atmospheric particle number [1]. While gas-phase H 2 SO 4 is reduced by molecular cluster formation and nucleation, its main sink is condensation on newly formed and pre-existing aerosol particles.…”

“…A key parameter in atmospheric mass transport calculations is the gas-phase diffusion coefficient (D), to which the condensation rate of vapour onto particle surface is proportional and dependent on the particle size [2]. Assessments of vapour concentrations [3] and modelling of particle growth and composition [4] are thus dependent on the values used for the binary diffusion coefficients. Under certain circumstances, the gas phase diffusion can even limit the overall rates of condensation and reactions of trace gases with aerosol particles via influencing the uptake of gas molecules onto the surface.…”