Production and Measurement of Organic Particulate Matter in the Harvard Environmental Chamber

Abstract

The production and the evolution of atmospheric organic particulate matter (PM) are insufficiently understood for accurate simulations of atmospheric chemistry and climate. The complex production mechanisms and reaction pathways make this a challenging research topic. To address these issues, an environmental chamber, providing enough residence time and close-to-ambient concentrations of precursors for secondary organic materials, is needed. The Harvard Environmental Chamber (HEC) was built to serve this need, simulating the production of gas and particle phase species from volatile organic compounds (VOCs). The HEC has a volume of 4.7 m 3 and a mean residence time of 3.4 h under typical operating conditions. It is operated as a completely mixed flow reactor (CMFR), providing the possibility of indefinite steady-state operation across days for sample collection and data analysis. The operation procedures are described in detail in this article. Several types of instrumentation are used to characterize the produced gas and particles. A High-Resolution Time-of-Fight Aerosol Mass Spectrometer (HR-ToF-AMS) is used to characterize particles. A Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) is used for gaseous analysis. Example results are presented to show the use of the environmental chamber in a wide variety of applications related to the physicochemical properties and reaction mechanisms of organic atmospheric particulate matter.

Joint Impacts of Acidity and Viscosity on the Formation of Secondary Organic Aerosol from Isoprene Epoxydiols (IEPOX) in Phase Separated Particles

“…Fine particulate matter (PM 2.5 ) is known to have significant effects on air quality, climate, and human health . Secondary organic aerosol (SOA) formed through the oxidation of volatile organic compounds (VOCs) comprises a large percentage of PM 2.5 mass in both field measurements and laboratory experiments. − As the non-methane VOC with the highest global emission rate, isoprene is also oxidized in the atmosphere to form significant amounts of SOA, , including through acid-catalyzed reactive uptake (or multiphase chemistry) of isoprene epoxydiols (IEPOX) onto sulfate aerosol particles. , The uptake coefficient of this reaction can be calculated by dividing the number of molecules lost to the surface with the total number of molecules striking the surface. Due to the relatively high reactive uptake coefficient of IEPOX onto existing sulfate particles, this process has been found to lead to substantial amounts of PM 2.5 , especially in forested areas with broadleaf trees such as the Southeastern United States and the Amazon rainforest. − Due to relatively large mass loadings of IEPOX-derived SOA in these areas, the physicochemical properties of IEPOX-derived SOA particles may have a significant influence on the subsequent formation and evolution of organic PM 2.5 . , Despite recent studies revealing the detailed reaction mechanisms of these multiphase chemical processes, few have explored whether IEPOX-derived SOA will alter the physicochemical properties of PM 2.5 . , …”

The Cooling Rate- and Volatility-Dependent Glass-Forming Properties of Organic Aerosols Measured by Broadband Dielectric Spectroscopy

“…Further reaction of ISOPOOH with OH radicals generate IEPOX, a semivolatile compound that can partition between particles and the gas phase . Heterogeneous reactions of IEPOX with acidified sulfate particles produce semivolatile condensed phase species, including 2-methyltetrol, alkene triols, and organosulfates such as 2-methyltetrol sulfates. , 2-Methyltetrol and 2-methyltetrol sulfates can account for up to 30 and 65% of the isoprene-derived SOA mass from the flow tube and chamber studies, respectively. − …”

Methodological advances to improve repeatability of SOA generation in environmental chambers

“…Organic aerosols (OAs) account for a large portion of Earth's fine particle mass budget (up to 90%, depending on the ecosystem), and of the total OA fine particle mass, secondary organic aerosol (SOA) accounts for its majority (70 -90%) (Fischer et al, 2020; 25 Claflin et al, 2018). SOA is aerosol that forms over multiple generations from the gas-phase oxidation of volatile organic compounds (VOCs) emitted from both biogenic and anthropogenic activity (Fischer et al, 2020;Zhang et al, 2018); yet, greater than two-thirds of the approximate 1000 Tg of non-methane VOCs emitted each year stem from biogenic sources (Claflin et al, 2018). To understand the dynamic between aerosols and their potential effect on the atmosphere, laboratory studies focused on the measurement and characterization of aerosols need to better 30 reflect the atmosphere.…”