Heterogeneous reactions between NO3 and N2O5 and diethyl sebacate (DES), glycerol, oleic acid (OA), linoleic acid (LA), and conjugated linoleic acid (CLA) were studied to understand better nighttime aerosol chemistry. The reactive uptake coefficient of NO3 on the liquid alkenoic acids (OA, LA, and CLA) was found to be >0.07, which is higher than previous results for unsaturated organics, including alkenoic acids. This reaction could potentially be an important loss process of particle-phase unsaturated organic compounds in the atmosphere and in laboratory secondary organic aerosol studies. The reactive uptake coefficient of N2O5 on liquid glycerol was also found to be relatively large with a value of (3.2-8.5)x10(-4), suggesting that N2O5 heterogeneous reactions with alcohols may also be atmospherically relevant. For all measurements with OA, CLA, and DES, the reactive uptake coefficients decreased significantly upon freezing. One possible explanation is that the liquid reaction is due to both a surface reaction and a bulk reaction and that the freezing process significantly decreases the importance of any bulk reactions. NO3 reactive uptake coefficients for liquid-phase compounds decreased in magnitude in the order: alkenoic acids>DES>glycerol. This is different compared to previous gas-phase studies and the difference may be due to the large viscosity of glycerol compared to the other organic compounds studied. N2O5 reactive uptake coefficients for liquid-phase compounds decreased in magnitude in the order: glycerol>LA>DES congruent with OA congruent with CLA.

Abstract. Recent atmospheric measurements show that biological particles are a potentially important class of ice nuclei. Types of biological particles that may be good ice nuclei include bacteria, pollen and fungal spores. We studied the ice nucleation properties of water droplets containing fungal spores from the genus Cladosporium, one of the most abundant types of spores found in the atmosphere. For water droplets containing a Cladosporium spore surface area of ∼217 µm 2 (equivalent to ∼5 spores with average diameters of 3.2 µm ), 1% of the droplets froze by −28.5 • C and 10% froze by -30

The carbon kinetic isotope effects (KIEs) of the room-temperature reactions of several light alkanes and ethene with OH radicals were measured in a 30 L PTFE reaction chamber at ambient pressure using gas chromatography coupled with online combustion and isotope ratio mass spectrometry (GCC-IRMS). For simplicity, KIEs are reported in per mil according to (‰) ) (k 12 /k 13 -1) × 1000. The following average KIEs were obtained, (all in ‰) : ethane, 8.57 ( 1.95; propane, 5.46 ( 0.35; n-butane, 5.16 ( 0.67; methylpropane, 8.45 ( 1.49; n-pentane, 2.85 ( 0.79; methylbutane, 2.91 ( 0.43; n-hexane, 2.20 ( 0.07; n-heptane, 1.96 ( 0.26; n-octane, 2.13 ( 0.39; cyclopentane, 1.84 ( 0.13; cyclohexane, 4.46 ( 0.51; methylcyclopentane, 1.77 ( 0.53; ethene, 18.6 ( 2.9. As well, the room-temperature rate constant for the reaction of methylcyclopentane + OH, not previously reported in the literature, was determined using relative rates: (8.6 ( 2.2) × 10 -12 cm 3 molecule -1 s -1 , including the estimated 25% uncertainty in the rate constant for cyclopentane + OH. KIE values for propane, n-butane and n-hexane have been reported previously [J. Geophys. Res. [Atmos.] 2000, 105, 29329]. Our KIE for n-hexane is in agreement with the previous measurement, but our values for propane and n-butane are both higher. The dependence between the KIE and chemical structure is discussed, and a method for estimating unknown carbon KIEs for the reactions of light alkanes with OH radicals is presented. With only one exception, predictions using this method agree within a factor of 2 of the experimental KIE results.

The carbon kinetic isotope effects (KIEs) of the room temperature reactions of benzene and several light alkyl benzenes with OH radicals were studied in a reaction chamber at ambient pressure using gas chromatography coupled with online combustion and isotope ratio mass spectrometry (GCC‐IRMS). The KIEs are reported in per mil according to ɛ (‰) = (KIE − 1) × 1000, where KIE = k12/k13. The following average KIEs were obtained, (all in ‰): benzene 7.53 ± 0.50; toluene 5.95 ± 0.28; ethylbenzene 4.34 ± 0.28; o‐xylene 4.27 ± 0.05, p‐xylene 4.83 ± 0.81; o‐ethyltoluene 4.71 ± 0.12 and 1,2,4‐trimethylbenzene 3.18 ± 0.09. Our KIE value for benzene + OH agrees with the only reported value known to us [Rudolph et al., 2000]. It is shown that measurements of the stable carbon isotope ratios of light aromatic compounds should be extremely useful to study atmospheric processing by the OH radical.

[1] Rust and bunt spores that act as ice nuclei (IN) could change the formation characteristics and properties of ice-containing clouds. In addition, ice nucleation on rust and bunt spores, followed by precipitation, may be an important removal mechanism of these spores from the atmosphere. Using an optical microscope, we studied the ice nucleation properties of spores from four rust species (Puccinia graminis, Puccinia triticina, Puccinia allii, and Endocronartium harknesssii) and two bunt species (Tilletia laevis and Tilletia tritici) immersed in water droplets. We show that the cumulative number of IN per spore is 5 × 10 À3 , 0.01, and 0.10 at temperatures of roughly À24°C, À25°C, and À28°C, respectively. Using a particle dispersion model, we also investigated if these rust and bunt spores will reach high altitudes in the atmosphere where they can cause heterogeneous freezing. Simulations suggest that after 3 days and during periods of high spore production, between 6 and 9% of 15 μm particles released over agricultural regions in Kansas (U.S.), North Dakota (U.S.), Saskatchewan (Canada), and Manitoba (Canada) can reach at least 6 km in altitude. An altitude of 6 km corresponds to a temperature of roughly À25°C for the sites chosen. The combined results suggest that (a) ice nucleation by these fungal spores could play a role in the removal of these particles from the atmosphere and (b) ice nucleation by these rust and bunt spores are unlikely to compete with mineral dust on a global and annual scale at an altitude of approximately 6 km.

Abstract. We studied the ice nucleation properties of 12 different species of fungal spores chosen from three classes: Agaricomycetes, Ustilaginomycetes, and Eurotiomycetes. Agaricomycetes include many types of mushroom species and are widely distributed over the globe. Ustilaginomycetes are agricultural pathogens and have caused widespread damage to crops. Eurotiomycetes are found on all types of decaying material and include important human allergens. We focused on these classes because they are thought to be abundant in the atmosphere and because there is very little information on the ice nucleation ability of these classes of spores in the literature. All of the fungal spores investigated contained some fraction of spores that serve as ice nuclei at temperatures warmer than homogeneous freezing. The cumulative number of ice nuclei per spore was 0.001 at temperatures between −19 °C and −29 °C, 0.01 between −25.5 °C and −31 °C, and 0.1 between −26 °C and −31.5 °C. On average, the order of ice nucleating ability for these spores is Ustilaginomycetes > Agaricomycetes ≃ Eurotiomycetes. The freezing data also suggests that, at temperatures ranging from −20 °C to −25 °C, all of the fungal spores studied here are less efficient ice nuclei compared to Asian mineral dust on a per surface area basis. We used our new freezing results together with data in the literature to compare the freezing temperatures of spores from the phyla Basidiomycota and Ascomycota, which together make up 98% of known fungal species found on Earth. The data show that within both phyla (Ascomycota and Basidiomycota), there is a wide range of freezing properties, and also that the variation within a phylum is greater than the variation between the average freezing properties of the phyla. Using a global chemistry–climate transport model, we investigated whether ice nucleation on the studied spores, followed by precipitation, can influence the transport and global distributions of these spores in the atmosphere. Simulations suggest that inclusion of ice nucleation scavenging of these fungal spores in mixed-phase clouds can decrease the annual mean concentrations of fungal spores in near-surface air over the oceans and polar regions, and decrease annual mean concentrations in the upper troposphere.

[1] The kinetic isotope effects (KIEs) for several ozonealkene reactions in the gas phase were studied in a 30 L PTFE reaction chamber. The time dependence of the stable carbon isotope ratios and the concentrations were determined using a gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS) system. The following average KIE values were obtained: 18.9 ± 2.8 (ethene), 9.5 ± 2.5

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