Aqueous phase oxidation of bisulfite influenced by nitrate photolysis

Nitrate aerosol is ubiquitous in the atmosphere, and it can exit in both solid aerosol particles and fog and cloud droplets. Nitrate in the aqueous and particulate phase can undergo photolysis to produce oxidizing active radicals, which will inevitably affect various atmospheric chemical processes. However, the role of nitrate aerosols in these atmospheric photochemical processes remains unclear. In this study, the effects of nitrate photolysis on the aqueous phase oxidation of bisulfite under different conditions were investigated. Results show that nitrate photolysis can significantly promote the oxidation of bisulfite to sulfate. It is found that pH plays a significant role in the reaction, and ammonium sulfate has significant impacts on regulating the pH of solution and the enhancement of sulfate production. We also found an apparent synergism among halogen chemistry, nitrate and its photochemistry and S(IV) aqueous oxidation, especially the oxidation of halide ions by the nitrate photolysis and by the intermediate peroxymonosulfuric acid (HSO5−) produced by the free radical chain oxidation of S(IV) in acidic solution leads to the coupling of the redox cycle of halogen with the oxidation of bisulfite, which promotes the continuous aqueous oxidation of bisulfite and the formation of sulfate. In addition, it is also found that O2 is of great significance on nitrate photolysis for the conversion of HSO3−, and H2O2 generation during the nitrate photolysis is verified. These results provide a new insight into the heterogeneous aqueous phase oxidation pathways and mechanisms of SO2 in cloud and fog droplets and haze particles.

Numerical simulation of chemical reactions occurring in fog droplets

<p><strong>Introduction</strong></p><p>Fog provides a significant medium for chemical reactions occurring in liquid phase. Fog droplets are relatively small (5 < r < 50 µm) hence the surface-to-volume ratio is large. Through the larger overall surface the absorption of inorganic and organic gases from different sources may be enhanced. Depending on the stability of fog, the chemical processes may have more time to take place in fog droplets. Also, ground based sources of solid aerosol particles and gases may be in direct connection with fog.</p><p>Inorganic and organic components may change the pH of fog droplets and significant amount of sulphate ion can be formed due to the oxidation (e.g. by hydrogen-peroxide and ozone) of dissolved sulphur-dioxide. At the same time there are some organic components, e.g. formaldehyde, which also react with the dissolved sulphur-dioxide but produces hydroxymethanesulfonic acid (HMSA), thus decreases the possibility of producing sulphate ion through oxidation. These competitive processes are important in understanding the formation of sulphate ion in solution. In addition, the liquid phase concentration of compounds and also the sulphate ion formation strongly depends on the size of the droplets. Physical and chemical processes in fog may have an impact on both the size distribution and solubility of solid aerosol particles.</p><p> </p><p><strong>Numerical model</strong></p><p>A box model with detailed microphysics and chemistry scheme with moving bin boundaries was used to simulate the following processes in fog:</p><ul><li>(i) Formation of drops on hygroscopic aerosol particles (ammonium-sulphate). Fog is formed due to cooling rate -0.0001 K/s.</li> <li>(ii) Condensational growth of drops.</li> <li>(iii) Scavenging of aerosol particles by water drops due to Brownian motion and phoretic forces.</li> <li>(iv) Absorption and desorption of inorganic (CO<sub>2</sub>, H<sub>2</sub>O<sub>2</sub>, O<sub>3</sub>, NH<sub>3</sub>, SO<sub>2</sub>) and organic (HCHO, HCOOH, CH<sub>3</sub>COOH) gases, dissociation, change of pH, sulphate formation (oxidation of S(IV) by hydrogen-peroxide and by ozone and reaction of formaldehyde with S(IV)).</li> </ul><p> </p><p><strong>Results</strong></p><p>Significant amount of HMSA formed in drops due to the reaction of S(IV) with formaldehyde. Taking into account this reaction, the amount of S(VI) formed is decreased compared to the case when no formaldehyde was present. Formation of HMSA modifies the solubility of the solid aerosol residue after evaporation of drops.</p>

A method for measuring total aerosol oxidative potential (OP) with the dithiothreitol (DTT) assay and comparisons between an urban and roadside site of water-soluble and total OP

An automated analytical system was developed for measuring the oxidative potential (OP) with the dithiothreitol (DTT) assay of filter extracts that include both water-soluble and water-insoluble (solid) aerosol species. Three approaches for measuring total oxidative potential were compared. These include using methanol as the solvent with (1) and without (2) filtering the extract, followed by removing the solvent and reconstituting with water, and (3) extraction in pure water and performing the OP analysis in the extraction vial with the filter. The water extraction method (the third approach, with filter remaining in the vial) generally yielded the highest DTT responses with better precision (coefficient of variation of 1–5 %) and was correlated with a greater number of other aerosol components. Because no organic solvents were used, which must be mostly eliminated prior to DTT analysis, it was easiest to automate by modifying an automated analytical system for measuring water-soluble OP developed by Fang et al. (2015). Therefore, the third method was applied to the field study for the determination of total OP. Daily 23 h filter samples were collected simultaneously at a roadside (RS) and a representative urban (Georgia Tech, GT) site for two 1-month study periods, and both water-soluble (OPWS-DTT) and total (OPTotal-DTT) OP were measured. Using PM2. 5 (aerodynamic diameter < 2.5 µm) high-volume samplers with quartz filters, the OPWS-DTT-to-OPTotal-DTT ratio at the urban site was 65 % with a correlation coefficient (r) of 0.71 (N = 35; p value < 0.01), compared to a ratio of 62 % and r = 0. 56 (N = 31; p value < 0.01) at the roadside site. The same DTT analyses were performed, and similar results were found using particle composition monitors (flow rate of 16.7 L min−1) with Teflon filters. Comparison of measurements between sites showed only slightly higher levels of both OPWS-DTT and OPTotal-DTT at the RS site, indicating both OPWS-DTT and OPTotal-DTT were largely spatially homogeneous. These results are consistent with roadway emissions as sources of DTT-quantified PM2. 5 OP and indicate that both soluble and insoluble aerosol components contributing to OP are largely secondary.

A method for measuring total aerosol oxidative potential (OP) with the dithiothreitol (DTT) assay and comparisons between an urban and roadside site of water-soluble and total OP

An automated analytical system was developed for measuring the oxidative potential (OP) with the dithiothreitol (DTT) assay of filter extracts that include both water-soluble and water-insoluble (solid) aerosol species. Three approaches for measuring total oxidative potential were compared. These include using methanol as the solvent with (1) and without (2) filtering the extract, followed by removing the solvent and reconstituting with water, and (3) extraction in pure water and performing the OP analysis in the extraction vial with the filter. The water extraction method (the third approach, with filter remaining in the vial) generally yielded highest DTT responses with better precision (coefficient of variation of 1–5 %), and was correlated with a greater number of other aerosol components. Because no organic solvents were used, which must be mostly eliminated prior to DTT analysis, it was the easiest to automate by modifying an automated analytical system for measuring water-soluble OP developed by Fang et al. (2015). Daily 23h filter samples were collected simultaneously at a roadside (RS) and a representative urban (GT) site for two one-month study periods, and both water-soluble (OPWS-DTT) and total (OPTotal-DTT) OP were measured. Using PM2.5 (aerodynamic diameter

Emission load of car service interiors

Car service centres are specific in terms of production of pollutants. The aim of the paper is to assess the quality of indoor environment of car service interiors with respect to the safe range of oxocarbon emission limits, concentration of gaseous and solid aerosols of selected chemical pollutants and occupational noise exposure. Measurements of concentration and exposure time indicated that the permitted limits were kept. CO concentration reached values in the range from 0 to 10 ppm, CO₂ concentration was observed in the range from 493 to 967 ppm. Concentration of solid aerosol of polyester bitumen reached the maximum value of 0.37 mg/m³, while for gaseous aerosol (e.g. toluene) it equalled 8.114 mg/m³. Measurements of chemical factors were carried out and evaluated by companies with appropriate accreditation. Occupational Exposure Limits (OELs) were higher in case of all selected substances. OEL was not demonstrably exceeded at any chemical factor. Noise emissions approached the limit values; therefore, hearing protection is required.

OPTICAL-ELECTRONIC METHOD FOR AEROSOL PARTICLES MEASUREMENT IN ENVIRONMENT

The description of the developed by us automatic Multichannel Aerosol Spectrometer “Masnik-A” are presented. “Masnik-A” system represents the optical/electronic automatic device for measuring of the concentrations and distributions of the sizes of liquid and solid aerosol particles of natural and artificial origin in laboratory and field conditions. Aerosol Spectrometer “Masnik-A” provides a range of measurement of the sizes of aerosol particles from 0.5 up to 40 mm (on a radius). It has 18 channels of the analyzer (graduations by the sizes) with a memory on the channel no less than 9.105 particles. The limiting value of measuring concentrations (containing in 1 cm3 of the aerosol environment) makes no less 2.104 particles. The instrument has possibility of obtaining the command of handle from external personal computer (PC), and also input of the results of measurements for further automatic processing by a specially developed program.