Ambient Gas-Particle Partitioning of Tracers for Biogenic Oxidation

Abstract

Exchange of atmospheric organic compounds between gas and particle phases is important in the production and chemistry of particle-phase mass but is poorly understood due to a lack of simultaneous measurements in both phases of individual compounds. Measurements of particle- and gas-phase organic compounds are reported here for the southeastern United States and central Amazonia. Polyols formed from isoprene oxidation contribute 8% and 15% on average to particle-phase organic mass at these sites but are also observed to have substantial gas-phase concentrations contrary to many models that treat these compounds as nonvolatile. The results of the present study show that the gas-particle partitioning of approximately 100 known and newly observed oxidation products is not well explained by environmental factors (e.g., temperature). Compounds having high vapor pressures have higher particle fractions than expected from absorptive equilibrium partitioning models. These observations support the conclusion that many commonly measured biogenic oxidation products may be bound in low-volatility mass (e.g., accretion products, inorganic-organic adducts) that decomposes to individual compounds on analysis. However, the nature and extent of any such bonding remains uncertain. Similar conclusions are reach for both study locations, and average particle fractions for a given compound are consistent within ∼25% across measurement sites.

Semivolatile POA and parameterized total combustion SOA in CMAQv5.2: impacts on source strength and partitioning

“…To achieve this end, atmospheric models routinely rely on estimates of volatility (i.e., vapor pressure or saturation concentration) and solubility in a predominantly aqueous phase. Although research efforts demonstrate clearly the importance of organic solubility in water on phase partitioning and particle viscosity Hodas et al, 2015;Pajunoja et al, 2015;Riipinen et al, 2015;Wania et al, 2015;Isaacman-VanWertz et al, 2016;Jathar et al, 2016b;Pye et al, 2017;Shiraiwa et al, 2017), improvements to the conceptual model of organic compounds partitioning into an organic-rich particulate phase alone are useful before the entire system is treated holistically.…”

A framework for expanding aqueous chemistry in the Community Multiscale Air Quality (CMAQ) model version 5.1

“…However, other studies have indicated that HMML may be a more dominant precursor to 2-MG (Nguyen et al, 2015). Additionally, we assume that the products of these aerosol and cloud aqueous pathways are nonvolatile, while monomeric species like 2-methyltetrols and 2-MG may be better represented as semivolatile (Isaacman-Van Wertz et al, 2016). These are areas that may be worthwhile to further refine in future development efforts, as more laboratory/field research becomes available, in an effort to better quantify the relative impacts of cloud vs. aerosol water production pathways on SOA mass.…”

“…In an effort to determine the optimal solver for our mechanism, we applied each KPP Rosenbrock solver with a positive definite adjustment (Sander et al, 2011) to over 20 000 scenarios (Table S5) representing a range of atmospheric conditions and then compared the results to a reference solution generated with the variable-coefficient ordinary differential equation solver (VODE). VODE is an initial-value ODE solver that uses variable-coefficient backward differentiation formula (BDF) methods for stiff systems and may be viewed as a successor to the Livermore solver for ordinary differential equations (LSODE) (Hindmarsh, 1983), which historically has been commonly applied to generate reference solutions for atmospheric chemistry problems (Brown et al, 1989;Sandu et al, 1997b). DVODE (VODE with double precision) was downloaded from the Netlib repository (http://www.netlib.org) and applied to the rate equations and Jacobian for the system of AQCHEM − KMT reactions to generate a reference solution as well as provide an independent check on the codes Table 2.…”

Observations of sesquiterpenes and their oxidation products in central Amazonia during the wet and dry seasons

“…Particle-phase composition is therefore critical for studying the importance of individual terpenes and terpene classes, but the dynamic gas-particle partitioning of these semi-volatile products requires the contemporaneous measurement of the difficult-to-measure gasphase components. Measurements of gas-particle partitioning and concentrations of biogenic OA tracers from isoprene and monoterpene oxidation have been reported previously as part of the Green Ocean Amazon (GoAmazon2014/5) field campaign (Isaacman-VanWertz et al, 2016), but few, if any, sesquiterpene oxidation products were identified in the dataset at that time. To fully characterize the sources of OA in the region, molecular-level and chemically specific signatures of oxidation products from a more complete range of BVOC precursors need to be identified and quantified.…”

“…Details of the instrument development and operation have been published previously (Isaacman-VanWertz et al, 2016;Isaacman et al, 2014;Kreisberg et al, 2009;Williams et al, 2006;Zhao et al, 2013) and we describe SV-TAG deployment briefly here. During the campaign, ambient air was pulled through a 15.24 cm ID duct at ∼ 5 m above ground level.…”