A comprehensive evaluation of enhanced temperature influence on gas and aerosol chemistry in the lamp-enclosed oxidation flow reactor (OFR) system.

Oxidation flow reactors (OFRs) have been widely used to investigate the formation of secondary organic aerosol SOA). However, the UV lamps that are commonly used to initiate photochemistry in OFRs can lead to increases in the reactor temperature with consequences that have not been assessed in detail. In this study, we systematically investigated the temperature distribution inside an Aerodyne Potential Aerosol Mass OFR and the associated impacts on flow and chemistry arising from lamp heating. A lamp-induced temperature enhancement was observed, which was a function of lamp driving voltage, number of lamps, lamp types, OFR residence time, and positions inside OFR. Under common OFR operational conditions (e.g., < 5 days of equivalent atmospheric OH exposure under low-NOx conditions), the temperature enhancement was usually within 1-5 °C. Under extreme (but less commonly used) settings, the heating could reach 15 °C. The influence of the increased temperature over ambient conditions on the flow distribution, gas, and condensed phase chemistry inside OFR was evaluated. We found that the increase in temperature changes the flow field, leading to a reduced tail on the residence time distribution and corresponding oxidant exposure due to faster recirculation. According to simulation results from a box model using radical chemistry, the variation of absolute oxidant concentration inside of OFR due to temperature increase was small (<5%). The temperature influences on existing and newly formed OA were also investigated, suggesting that the increase in temperature can impact the yield, size, and oxidation levels of representative biogenic and anthropogenic SOA types. Recommendations for temperature-dependent SOA yield corrections and OFR operating protocols that mitigate lamp-induced temperature enhancement and fluctuations are presented. We recommend blowing air around the outside of the reactor with fans during OFR experiments to minimize the temperature increase inside OFR. Temperature increases are substantially lower for OFRs using less powerful lamps than the Aerodyne version. [ABSTRACT FROM AUTHOR]