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Discussion papers
https://doi.org/10.5194/acp-2018-1355
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1355
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Jan 2019

Research article | 14 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Photolytically-Generated Sulfuric Acid and Particle Formation: Dependence on Precursor Species

David R. Hanson1, Hussein Abdullahi1, Seakh Menheer1, Joaquin Vences1, Michael R. Alves1,2, and Joan Kunz1 David R. Hanson et al.
  • 1Chemistry Department, Augsburg University, Minneapolis, MN 55454, USA
  • 2Chemistry and Biochemistry, University of California - San Diego, La Jolla, CA 92093, USA

Abstract. Size distributions of particles formed from sulfuric acid (H2SO4) and water vapor in a Photolytic Flow Reactor (PhoFR) were measured with a nano-particle mobility sizing system. Experiments with added ammonia and dimethylamine were also performed. H2SO4(g) was synthesized from HONO, sulfur dioxide, and water vapor, initiating OH oxidation by HONO photolysis. For standard reactant flows and conditions, 296 K, 52 % relative humidity, and a ~ 40 s residence time, the calculated concentration of H2SO4 peaked at 1.2 × 1010 cm−3, measured particle mean diameter was ~ 6 nm and total number density was ~ 104 cm−3. Measured distributions were influenced by molecular clusters at small sizes, less than or equal to 2 nm diameter, but were generally dominated by large particles that are roughly log-normal with mean diameters ranging up to 12 nm and a relatively constant lnσ of ~ 0.3. Particle number density and their mean size depended on relative humidity, HONO concentration, illumination, and SO2 level. Particle formation conditions were stable over many months. Addition of single-digit pmol/mol mixing ratios of dimethylamine led to very large increases in number density. Ammonia at levels up to 2000 pmol/mol showed that NH3 is less effective than dimethylamine at producing particles. A two-dimensional simulation of PhoFR reveals that H2SO4 scales with HONO and its level builds along the length of the flow reactor. Experimentally, particle growth scaled with HONO, in accord with model-predicted H2SO4 levels. Additional comparison between experiment and model indicates that reaction of HO2 with SO2 could be a significant source of H2SO4 in this experiment. The effects of potential contaminants on particle formation rates near room temperature are addressed and provide context in comparisons with previous experiments. The added-base experimental results provide support for previously published dimethylamine-H2SO4 cluster thermodynamics but do not support previously published ammonia-sulfuric acid thermodynamics.

David R. Hanson et al.
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Short summary
Particle formation was studied in a flow reactor with photolytic generation of sulfuric acid. Results are in agreement with many previous results and also confirm that some are outliers. Addition of single-digit pmol/mol mixing ratios of dimethylamine led to very large increases in number density. Ammonia additions showed that it is less effective than dimethylamine at producing particles. Model simulations reveal results are congruent with previous dimethylamine-sulfuric acid thermodynamics.
Particle formation was studied in a flow reactor with photolytic generation of sulfuric acid....
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