Rate Coefficients for the Gas-Phase Reactions of Nitrate Radicals with a Series of Furan Compounds.

The atmospheric reaction of a series of furan compounds (furan (F), 2-methylfuran (2-MF), 3-methylfuran (3-MF), 2,5-dimethylfuran (2,5-DMF), and 2,3,5-trimethylfuran (2,3,5-TMF)) with nitrate radical (NO3) has been investigated using the relative rate kinetic method in the CHamber for the Atmospheric Reactivity and the Metrology of the Environment (CHARME) simulation chamber at the laboratoire de Physico-Chimie de l'Atmosphere (LPCA) laboratory (Dunkerque, France). The experiments were performed at (294 ± 2) K atmospheric pressure and under dry conditions (relative humidity, RH < 2%) with proton transfer mass reaction-time of flight-mass spectrometer (PTR-ToF-MS) for the chemical analysis. The following rate coefficients (in units cm3 molecule-1 s-1) were determined: furan, k(F) = (1.51 ± 0.38) × 10-12, 2-methylfuran, k(2-MF) = (1.91 ± 0.32) × 10-11, 3-methylfuran, k(3-MF) = (1.49 ± 0.33) × 10-11, 2,5-dimethylfuran, k(2,5-DMF) = (5.82 ± 1.21) × 10-11, and 2,3,5-trimethylfuran, k(2,3,5-TMF) = (1.66 ± 0.69) × 10-10. The uncertainty on the measured rate coefficient (ΔkFC) includes both the uncertainty on the measurement and that on the rate coefficient of the reference molecule. To our knowledge, this work represents the first determination for the rate coefficient of the 2,3,5-TMF reaction with NO3. This work shows that the reaction between furan and methylated furan compounds with nitrate radical (NO3) is the dominant removal pathway during the night with lifetimes between 0.5 and 55 min for the studied molecules.

Hygroscopic growth and CCN activity of secondary organic aerosol produced from dark ozonolysis of γ-terpinene.

The hygroscopic growth factor (GF) and cloud condensation nuclei (CCN) activity of secondary organic aerosol (SOA) particles produced during dark ozonolysis of γ-terpinene under different reaction conditions were investigated. The SOA particles were produced in the presence or absence of cyclohexane, an OH scavenger; 1,3,5-trimethylbenzene, an anthropogenic volatile organic compound; and (NH4)2SO4 seed particles. A hygroscopicity tandem differential mobility analyzer was used to determine the GFs of the SOA particles at RHs ≤ 93%. For some experiments, a CCN counter was used for size-resolved measurement of CCN activation at supersaturation (S) in the range of 0.1 to 1%. The single hygroscopicity parameter κ was derived from both the GF and CCN measurements. Under subsaturated conditions, all the SOA (except those in the presence of the (NH4)2SO4 seeds) showed small GF values. These GFs demonstrated that SOA mass loading affected the GF. A decrease in the SOA mass loading led to increased GF and corresponding κGFvalues. However, in a supersaturation regime, the SOA mass loading and the size of the particles did not significantly alter the CCN activity of the SOA. Our CCN measurements showed higher κCCN values (κCCN = 0.20-0.24) than those observed in most monoterpene ozonolysis studies (κCCN = 0.1-0.14). This difference may have been due to the presence of the two endocyclic double bonds in the γ-terpinene structure, which may have affected the SOA chemical composition, in contrast to monoterpenes that contain an exocyclic double bond. Our comparisons of sub- and supersaturated conditions showed a larger range of κ values than other experiments. Average κCCN/κGF ratios of ~7 and 14 were obtained in the unseeded SOA experiments at low and high SOA mass loadings, respectively. The average κCCN of 0.23 indicated that the SOA produced during ozonolysis of γ-terpinene exhibited fairly high CCN activity.