The Chamber Wall Index for Gas–Wall Interactions in Atmospheric Environmental Enclosures

Abstract

Secondary organic aerosol (SOA) particles, which are formed and aged in Earth’s oxidizing atmosphere, influence climate and human health. Quantifying properties of SOA particles and semi-volatile organic compounds (SVOCs) requires controlled experiments in enclosures, but, unfortunately, enclosures have walls that can alter the chemistry. Large environmental chambers (ECs) and portable oxidative flow reactors (OFRs) are widely used, but comparing wall effects for these different chambers is difficult. In this paper, the Chamber Wall Index (CWI) is developed as the ratio of the initial wall uptake time constant divided by the enclosure residence time. This index demonstrates that walls will alter the chemistry less in OFRs than in ECs, due primarily to shorter residence times. Much shorter residence times may not be feasible because oxidation chemistry needs time to produce atmospherically relevant SOA and SVOCs. While all current OFRs have wall effects, it may be possible to develop a “wall-less” OFR.