Ozone–isoprene reactions: Product formation and aerosol potential

Abstract

AbstractDark‐phase experiments between isoprene and O3 are discussed. UNC outdoor chamber experiments have shown that in high‐concentration systems of isoprene and O3 (5 ppm C and 1 ppm) approximately 75% of the reacted carbon can be observed in the product formation of HCHO, CO, methacrolein, methylvinylketone, methylglyoxal, acetaldehyde, and propylene. Mechanisms were developed which gave reasonable fits to dark‐phase chamber experiments of MACR, MVK, isoprene, and O3. Experimental data and modeling results were used to generate O3 rates of attack on MVK and MACR. An isoprene–O3 rate of 1.67 × 10−2 ppm−1·min−1 was used and is consistent with other rates reported in the literature. Dark isoprene–O3 systems appear to form homogeneously nucleated aerosol. Most of these particles appear and remain at diameters well below the optical cutoff region (0.3–0.5 μm), as opposed to the particles from similar α‐pinene–O3 systems, which also form at smaller sizes but then grow into the optical size range (0.5 μm). Lower concentrations of α‐pinene and O3 (0.2 ppm C and 0.12 ppm) still generated substantial aerosol, but by comparison, rapid CN nucleation was not observed during a similar side‐by‐side system of isoprene and O3.