Hydroxyl and nitrate radical oxidation of agricultural reduced sulfur compounds in the presence of amines

Authors: VAN ROOY, PAUL - University Of California; PURVIS-ROBERTS, KATHLEEN - Claremont Colleges; Silva, Philip - Phil; CROCKER III, DAVID - Dominican University Of California

Submitted to: American Association for Aerosol Research
Publication Type: Abstract Only
Publication Acceptance Date: 4/18/2018
Publication Date: 9/7/2018
Citation: Van Rooy, P., Purvis-Roberts, K., Silva, P.J., Crocker Iii, D.R. 2018. Hydroxyl and nitrate radical oxidation of agricultural reduced sulfur compounds in the presence of amines. American Association for Aerosol Research. Paper No. 5.

Interpretive Summary:

Technical Abstract: Gas-phase reduced sulfur compounds, such as dimethylsulfide, dimethyldisulfide, methanethiol, and hydrogen sulfide, are known to be emitted and are present around agricultural areas. Products formed through the oxidation of reduced sulfur compounds, especially dimethylsulfide, are also thought to be important to new particle formation and particle growth over the ocean. Gas-phase amines, like trimethylamine, diethylamine, and butylamine, are also emitted around agricultural areas and are also considered to be important to new particle formation. Potential sources of both these compounds in agriculture are animal waste, silage, and direct enteric emissions. While chamber studies have shown amines can oxidize to form substantial mass concentration of secondary aerosol, there have been few chamber studies focused on mass yields and aerosol properties of secondary aerosols formed through the oxidation of reduced sulfurs. Similarly, there have been no major chamber studies investigating how these two emitted compound classes interact to form secondary aerosol. To probe the properties of secondary aerosol formed through the oxidation of reduced sulfurs in the presence of amines, a series of both single and multiple precursor experiments were conducted in a 37.5 cubic meter chamber at the University of California, Riverside. Experiments were conducted in under both dry and humid conditions utilizing either nitrate radical (300ppb) or hydroxyl radical (1ppm) as an oxidant. During single precursor experiments, 100ppb of a single amine or reduced sulfur was injected into the chamber. During multiple precursor experiments, 100ppb of a reduced sulfur as well as 100ppb of an amine was injected into the chamber. In most cases, multiple precursor experiments formed secondary aerosol mass concentrations substantially larger than either of the individual precursor experiments. For example, hydroxyl radical oxidation of methanethiol with diethylamine formed over 55 micrograms per cubic meter of aerosol while the individual precursors formed less than 15 and 10 micrograms per cubic meter, respectively. The composition of the secondary aerosol that formed during each experiment was measured using a High Resolution-Time of Flight-Aerosol Mass Spectrometer. Multiple precursor experiments tend to form more oxidized organic sulfur compounds as compared to the single precursor reduced sulfur experiments. The presence of humidity had a profound impact on the composition of the secondary aerosol formed during single precursor reduced sulfur experiments as well as multiple precursor experiments. During dry experiments organic-sulfur compounds were prone to grow in, while during humid experiments these compounds were largely absent and replaced by sulfate aerosol, likely sulfuric acid. The type of oxidant played a paramount role in the composition and mass yield of the amines. Amines oxidized by the nitrate radical often reacted quickly and formed nitrate salts; aerosol formed through hydroxyl radical oxidation of amines was more gradual and lacked nitrate salts. Surprisingly, during some multiple precursor experiments, such as trimethylamine with dimethyldisulfide, the composition of the secondary aerosol that formed was nearly identical regardless of the oxidant. This novel investigation provides insight into the important role that amines and reduced sulfurs play in the formation of secondary aerosols, especially around agricultural areas.