Atmospheric Chemistry in a Box or a Bag

Abstract

Environmental chambers have proven to be essential for atmospheric photochemistry research. This historical perspective summarizes chamber research characterizing smog. Experiments with volatile organic compounds (VOCs)-nitrogen oxides (NO x ) have characterized O 3 and aerosol chemistry. These led to the creation and evaluation of complex reaction mechanisms adopted for various applications. Gas-phase photochemistry was initiated and developed using chamber studies. Post-1950s study of photochemical aerosols began using smog chambers. Much of the knowledge about the chemistry of secondary organic aerosols (SOA) derives from chamber studies complemented with specially designed atmospheric studies. Two major findings emerge from post-1990s SOA experiments: (1) photochemical SOAs hypothetically involve hydrocarbons and oxygenates with carbon numbers of 2, and (2) SOA evolves via more than one generation of reactions as condensed material exchanges with the vapor phase during "aging". These elements combine with multiphase chemistry to yield mechanisms for aerosols. Smog chambers, like all simulators, are limited representations of the atmosphere. Translation to the atmosphere is complicated by constraints in reaction times, container interactions, influence of precursor injections, and background species. Interpretation of kinetics requires integration into atmospheric models addressing the combined effects of precursor emissions, surface exchange, hydrometeor interactions, air motion and sunlight.

PyCHAM: CHemistry with Aerosol Microphysics in Python

“…PyCHAM (CHemistry with Aerosol Microphysics in Python) is an open-access 0-D box model for aerosol chamber studies. Aerosol chambers provide a means for atmospheric scientists to interrogate aerosol processes (Finlayson-Pitts & Pitts, 2000;Hidy, 2019;Schwantes et al, 2017). Allying PyCHAM with chamber measurements allows quantification of unknown parameters, such as branching ratios for oxidation schemes (Chen & Griffin, 2005).…”

PyCHAM (v2.1.1): a Python box model for simulating aerosol chambers

“…Aerosol chambers (interchangeably called smog chambers), defined as those used for interrogating gas-and particle-phase processes, provide a method for isolating specific processes of interest without the conflating effects present in the ambient atmosphere. Ultimately, the goal of the chamber is to improve understanding and quantitative constraints on the evolution of the physicochemical properties of the gas and particle phase (Schwantes et al, 2017;Charan et al, 2019;Hidy, 2019). A description of chamber processes first requires consideration of the chamber characteristics, including wall material (frequently fluorinated ethylene-propene film -FEP Teflon -though others are used), lighting and dimensions.…”

“…molecules cm −3 s −1 , and the Jacobian matrix is specified at each integration step. The ordinary differential equations (ODEs) for these processes are solved by the backward differentiation formula, the utility of which has been demonstrated in similar atmospheric applications (Jacobson, 2005), from the SciPy package for scientific computing in Python.…”

“…through comparison with Fig. 16.1 of Jacobson, 2005). By default PyCHAM assumes an ideal system with no particle-phase mass transfer limitation to partitioning.…”

Captive Aerosol Growth and Evolution (CAGE) chamber system to investigate particle growth due to secondary aerosol formation

“…A few chamber systems have been designed to be portable (Shibuya et al, 1981;Hennigan et al, 2011;Bonn et al, 2013;Platt et al, 2013;Kaltsonoudis et al, 2019;Vu et al, 2019). Several comprehensive reviews of existing environmental chambers have been published (Becker, 2006;Lee et al, 2009;70 Seakins, 2010;Hidy, 2019).…”