Observation of rates and products in the reaction of NO3 with submicron squalane and squalene aerosol
The reactive uptake coefficients γ, for nitrate radical, NO3, on ∼100 nm diameter squalane and squalene aerosol were measured (1 atm pressure of N2 and 293 K). For squalane, a branched alkane, γNO3 of 2.8 × 10−3 was estimated. For squalene which contains 6 double bonds, γNO3 was found to be a function of degree of oxidation with an initial value of 0.18 ± 0.03 on fresh particles increasing to 0.82 ± 0.11 on average of over 3 NO3 reactions per squalene molecule in the aerosol. Synchrotron VUV-ionization aerosol mass spectrometry was used to detect the particle phase oxidation products that include as many as 3 NO3 subunits added to the squalene backbone. The fraction of squalene remaining in the aerosol follows first order kinetics under oxidation, even at very high oxidation equivalents, which suggests that the matrix remains a liquid upon oxidation. Our calculation indicates a much shorter chemical lifetime for squalene-like particle with respect to NO3 than its atmospheric lifetime to deposition or wet removal.