Review of Hanson et al. Measurement Report: Sulfuric Acid Nucleation and Experimental Conditions in a Photolytic Flow Reactor

Abstract

The article presents upgrades to a photolytic flow reactor system to study nucleation of sulfuric acid and presents some new results using the system. Although sulfuric acidwater (+base) nucleation has been studied extensively by different teams, there are discrepancies in the results obtained using different measurement equipment, so there is a need for validating earlier studies and improving the measurements. Therefore I think the article is in principle worth publication as measurement report. However, the article needs revision for clarity and more discussion on the uncertainties. The authors believe that the differences in their new results compared to their earlier study (Hanson et al. 2019) is due to improved cleanliness of the system, but since there are no actual measurements of the contaminants this remains speculative. Also, the