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 (NOx) have characterized O3 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.
Highlights
Atmospheric processes are a blend of meteorological phenomena, air chemistry and interactions with the hydro, pedo- and biosphere
Evaluation of secondary organic aerosol (SOA) models using smog chamber data follows from a history of evaluations of gas-phase mechanisms
Simulation of atmospheric photochemical kinetics began in the 1950s
Summary
Atmospheric processes are a blend of meteorological phenomena, air chemistry and interactions with the hydro-, pedo- and biosphere. Research strategies have applied separate, fundamental results of physics, chemistry and biology to construct conceptual models leading to current understanding of the atmospheric chemical dynamics An adjunct to these applications includes laboratory simulation of different processes believed to be relevant to the atmosphere [1]. Particle concentrations following the diurnal changes in photochemical smog pointed to a chemical link distinct from smoke or dust emissions This conjecture was verified early on in laboratory experiments of Renzetti and colleagues [8,9,10], who irradiated auto exhaust in a reactor with and without sulfur dioxide (SO2 ). Gas-phase photochemical processes involving NOx and VOC relevant to urban conditions took precedence through the 1980s with combined bench scale experiments and smog chamber research actively pursued at the at SAPRC, for example, and later at the University of North Carolina, Carnegie Mellon University and the US Environmental Protection Agency (EPA). Review of autoxidation and highly oxygenated organic molecules (HOM) in atmospheric chemistry
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