Index Geophysics

Formation and chemical aging of secondary organic aerosol during the β-caryophyllene oxidation

The secondary organic aerosol (SOA) production during the oxidation of &beta;-caryophyllene by ozone (O₃) and hydroxyl radicals (OH) and the subsequent chemical aging of the products during reactions with OH were investigated. Experiments were conducted with ozone and with hydroxyl radicals at low NO_<i>x</i> (zero added NO_<i>x</i>) and at high NO_<i>x</i> (hundreds of parts per billion). The SOA mass yield at 10 μg m⁻³ of organic aerosol was 27% for the ozonolysis, 20% for the reaction with OH at low NO_<i>x</i>, and 38% at high NO_<i>x</i> under dry conditions, 20 °C, and ozone excess. Parameterizations of the fresh SOA yields have been developed. The average fresh SOA atomic O : C ratio varied from 0.24 to 0.34 depending on the oxidant and the NO_<i>x</i> level, while the H : C ratio was close to 1.5 for all systems examined. An average density of 1.06 ± 0.1 μg m⁻³ of the β-caryophyllene SOA was estimated. The exposure to UV light had no effect on the &beta;-caryophyllene SOA concentration and aerosol mass spectrometer (AMS) measurements. The chemical aging of the β-caryophyllene SOA produced was studied by exposing the fresh SOA to high concentrations (10⁷ molecules cm^&minus;3) of OH for several hours. These additional reactions increased the SOA concentration by 15–40% and O : C by approximately 25%. A limited number of experiments suggested that there was a significant impact of the relative humidity on the chemical aging of the SOA. The evaporation rates of β-caryophyllene SOA were quantified by using a thermodenuder allowing us to estimate the corresponding volatility distributions and effective vaporization enthalpies.

Tasoglou, A.

Pandis, S. N.

2018-09-10

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10.5194/acp-15-6035-2015

https://acp.copernicus.org/articles/15/6035/2015/

eISSN: 1680-7324

eng