Xi Shu

Products and kinetics of the heterogeneous reaction of suspended vinclozolin particles with ozone.

Vinclozolin is a widely used fungicide that can be released into the atmosphere via application and volatilization. This paper reports an experimental investigation on the heterogeneous ozonation of vinclozolin particles. The ozonation of vinclozolin adsorbed on azelaic acid particles under pseudo-first-order conditions is investigated online with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The ozonation products are analyzed with a combination of VUV-ATOFMS and GC/MS. Two main ozonation products are observed. The formation of the ozonation products results from addition of O(3) on the C-C double bond of the vinyl group. The heterogeneous reactive rate constant of vinclozolin particles under room temperature is (2.4 ± 0.4) × 10(-17) cm(3) molecules(-1) s(-1), with a corresponding lifetime at 100 ppbv O(3) of 4.3 ± 0.7 h, which is almost comparable with the estimated lifetime due to the reaction with atmospheric OH radicals (∼1.7 h). The reactive uptake coefficient for O(3) on vinclozolin particles is (6.1 ± 1.0) × 10(-4).

Heterogeneous reactions of suspended parathion, malathion, and fenthion particles with NO3 radicals

Organophosphorus pesticides (OPPs) emit into the atmosphere in both gas and particulate phases via spray drift from treatments and post-application emission, but most of their degradations in the atmosphere are not well known. In this study, the heterogeneous reactions of nitrate (NO(3)) radicals with three typical OPPs (parathion, malathion, and fenthion) absorbed on azelaic acid particles are investigated using an online vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The reaction products observed with the VUV-ATOFMS are identified on the basis of GC/MS analysis of the products in the reaction between NO(3) radicals and the coating of the pesticide. Paraoxon is identified as the only product of parathion; malaoxon and bis(1,2-bis-ethoxycarbonylethyl)disulfide as the products of malathion; fenoxon, fenoxon sulfoxide, fenthion sulfoxide, fenoxon sulfone, and fenthion sulfone as the products of fenthion. The degradation rates of parathion, malathion, and fenthion under the experimental conditions are 5.5×10(-3), 5.6×10(-2), and 3.3×10(-2)s(-1), respectively. The pathways of the heterogeneous reactions between the three OPPs and NO(3) radicals are proposed. The experimental results reveal the possible transformations of these OPPs through the oxidation of NO(3) radicals in the atmosphere.

Ozonation of trifluralin particles: an experimental investigation with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer.

The ozonation of trifluralin coated on azelaic acid particles is investigated with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer. The suspended trifluralin particles with the mean diameter of 270nm react with approximately 100ppm ozone in an aerosol reaction chamber under ambient pressure and room temperature (1atm, 298K). The time-of-flight mass spectra of the trifluralin particles and the solid state ozonides are obtained. The assignments of the mass spectra reveal that the major primary ozonides of trifluralin particles are 2,6-dinitro-N-propyl-N-propanoyl-4-(trifluoromethyl) benzamine and 2,6-dinitro-N-(propan-2(and 3)-ol)-N-propyl-4-(trifluoromethyl) benzamine. The major secondary ozonides of trifluralin 2-ethyl-7-nitro-5-(trifluoromethyl) benzimidazole-3-oxide, 2,6-dinitro-N-propyl-4-(trifluoromethyl) benzenamine and 2,6-dinitro-N-(formyl)-N-propyl-4-(trifluoromethyl) benzamine are observed. The primary ozonides are directly resulted from the oxidation of N-propyl groups. The pathways of the primary ozonation are proposed in the paper.

Heterogeneous Reactions of Pirimiphos-Methyl and Pirimicarb with NO3 Radicals

Pirimiphos-methyl (PMM) and pirimicarb (PM) are two typical N,N-dialkyl substituted pyrimidine pesticides. The heterogeneous reactions of suspended PMM and PM particles with NO(3) radicals are investigated using an online aerosol time-of-flight mass spectrometer and a real-time atmospheric gas analysis mass spectrometer. Three products for PMM and five products for PM are observed and assigned with the aid of GC/MS. Phosphoric acid 2-diethylamino-6-methyl-4-pyrimidinyl dimethyl ester and 2-(dimethylamino)-5,6-dimethyl-4-hydroxy-pyrimidine are the main reaction products observed for PMM and PM, respectively. The effective rate constants for the reactions of PMM and PM particles with NO(3) radicals are (9.9 ± 0.3) × 10(-12) and (7.5 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), respectively, obtained using a mixed-phase relative rate method. Geometries and energies of transition states (TS) and intermediates (IM) are obtained by DFT calculation to elucidate the detailed mechanism of the P═S group oxidation into the P═O group for PMM. The theoretical studies present the reasonable intermediates including the S-oxide and the diradical (IM1(a) and IM2(a)). The mechanism explanation may provide useful information for understanding the degradation mechanism of organothionophosphorus compounds in the environment.

Online MALDI-TOF MS using an aerodynamic lens assembly as a direct deposition interface.

This technical note reports a design utilizing an aerodynamic lens assembly to transport suspended sample particles directly onto the target plate and conduct in situ MALDI analysis. The design provides a new alternative method for online MALDI analysis. The matrix/analyte/salt-contained particles sampled by a nozzle are focused into a particle beam with an aerodynamic lens assembly and then deposited on the target plate directly. The deposited particles are in situ desorbed/ionized by a 266 nm laser beam with an incidence angle of 50 degrees. The generated ions are detected with a reflectron mass spectrometer capable of delayed ion extraction and ion gating. The MALDI-TOF mass spectra of poly(ethylene glycol) (PEG) 1000, 2000, and 4000 particles are obtained in the experiment. The initial experimental results demonstrate that the design can be used for online MALDI analysis.

Heterogeneous reaction of suspended phosmet particles with NO3 radicals.

As an organophosphorous insecticide, phosmet is widely used for plant protection as well as against the ectoparasites on productive livestock. It emits into the atmosphere in both gas and particulate phases via spray drift from treatments and postapplication emissions, but its degradation in the atmosphere is not well-known up to now. In this study, the heterogeneous reaction of phosmet absorbed on the azelaic acid particles with NO(3) radicals is investigated in real-time using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). Two primary products and their nitro-substituted derivates are observed. The apparent reaction rate of phosmet particles with NO(3) radicals is also obtained by a relative rate method with isoprene and 1,4-cyclohexadiene as the reference compounds. The concentrations of the reference substance and phosmet particles are synchronously detected with an atmospheric gas analysis mass spectrometer and the VUV-ATOFMS. Under the experimental conditions, the average apparent reaction rate obtained is (1.92 ± 0.09) × 10(-12) cm(3) molecule(-1) s(-1), and the corresponding atmospheric lifetime toward NO(3) radicals is roughly estimated to be ~0.3 h.

Vacuum Ultraviolet Photoionization Mass Spectra of Typical Organics Contained in Ambient Aerosols

ABSTRACT This paper reports an investigation on typical organics contained in ambient aerosols with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The VUV-ATOFMS utilizes a vacuum ultraviolet krypton lamp as an ionization source. The single- and multi-constituent particles generated with typical atmospheric organics (n-eicosane, n-triacontane, 1-pentadecanol, 1-eicosanol, hexanoic acid, decanoic acid, heptadecanoic acid, oleic acid, succinic acid, pyrene, vanillin, benzoic acid, terephthalic acid, and D-galactose) are analyzed with VUV-ATOFMS. The time-of-flight mass spectra of all organic particles are obtained except hexanoic acid. The mass spectra reveal that the detection efficiencies for a certain compound contained in multi-constituent and single-constituent particles are different. These discrepancies may result from the different evaporation dynamics of aerosols in both atomization and vaporization processes. The pyrene has the strongest signal intensity in single- or multi-constituent aerosols, indicating that the VUV-ATOFMS performs well in detecting polycyclic aromatic hydrocarbons. These experimental results present a view on the VUV-photoionization mass spectra of the 14 typical organics contained in ambient aerosols.

Heterogeneous ozonolysis of pirimicarb and isopropalin: mechanism of ozone-induced N-dealkylation and carbonylation reactions

N,N-Dialkyl-substituted pyrimidine and N,N-dialkylaniline are basic structures for many pesticides. In this study, the heterogeneous reactions of O-3 with pirimicarb and isopropalin adsorbed on silica particles are investigated. The N-dealkylation and carbonylation of the N,N-dialkyl group have been observed as the important reaction pathways for both pirimicarb and isopropalin. The measured effective rate constants for pirimicarb and isopropalin under room temperature (298 +/- 2K) are 1.45 x 10(-18) (s.d. +/- 0.17) and 2.70 x 10(-19) cm(3) molecules(-1) s(-1) (+/- 0.27). The corresponding half-life for the particulate pirimicarb and isopropalin are 5.6 and 30 days, assuming an average tropospheric ozone concentration of 40 ppbv. Detailed reaction mechanisms are proposed for the first time based on the density functional theory calculations. In addition, the transformation of -NO2 into -NHOH is observed in the ozonolysis of isopropalin, which has not been reported in previous studies.

Lipid fingerprinting of Bacillus spp. using online MALDI-TOF mass spectrometry

Rapid identification of Bacillus spores has attracted great interest in the medical and forensic communities due to the highly pathogenic nature of certain Bacillus species and its potential application in bioweapons. In this study, we evaluated the feasibility of rapid and reliable identification of several Bacillus spp. (B. subtilis, B. cereus, B. megaterium, B. pumilus, and B. sphaericus) using online MALDI-TOF mass spectrometry combined with lipid profiling. The bacterial cultures in liquid medium were extracted with methanol and chloroform, and the extracts were aerosolized into droplets and immediately analyzed with an online MALDI-TOF mass spectrometer. Results showed that phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and diglycosyldiacylglycerol (DGDG) were present in the mass spectra, as alkali metal adducts. The unique lipid profiles obtained from these Bacillus spp. allowed us to differentiate between them. The reliability and reproducibility of the rapid identification method for Bacillus were tested under different experimental conditions. An alternative online chemotaxonomic method for bacterial identification is demonstrated.

Experimental studies on ozonation of ethylenethiourea

The experimental study on ozonation of ethylenethiourea (ETU) is conducted. The reaction of gas-phase ETU with 0.63 x 10(-6) mol/L ozone is carried out in a 200-L reaction chamber. The secondary organic aerosol (SOA) resulted from the ozonation of gas-phase ETU is observed with a scanning mobility particle size (SMPS). The rapid exponential growth of SOA reveals that the atmospheric lifetime of ETU vapor towards ozone reaction is less than four days. The ozonation of dry ETU particles, ETU-contained water droplets and ETU aqueous solution is investigated with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The formation of 2-imidazoline is observed in the ozonation of dry ETU particles and ETU-contained water droplets. The formation of 2-imidazoline and ethylenerea is observed in the ozonation of ETU aqueous solution.