Journal of Atmospheric Chemistry最新文献

Very short-lived substances (VSLs) are known to play an important role in ozone depletion in the troposphere and stratosphere. Environmental factors that influence the production of these compounds by marine phytoplankton, which is known to be the source of these compounds in open oceans, have not yet been well studied. Here we examined the effects of light intensity on the production of VSLs by the marine diatom Ditylum brightwellii. Bromodichloromethane (CHBrCl₂), dibromochloromethane (CHBr₂Cl), bromoform (CHBr₃), chloroform (CHCl₃), and dibromomethane (CH₂Br₂) in cultures incubated under full spectrum daylight intensities of 30, 60, and 120 µmol photons m^− 2 s^− 1 were measured using purge and trap gas chromatograph–mass spectrometry. Phytoplankton growth was monitored by measuring chlorophyll-a concentration and cell density. Both the chlorophyll-a concentration (the cell density) and the production rates of VSLs increased with increasing light intensity. The maximum production rates of CHBrCl₂, CHBr₂Cl, CHBr₃, CHCl₃, and CH₂Br₂ were observed during the exponential or stationary phase, with the exception of CH₂Br₂ incubated under 30 µmol photons m^− 2 s^− 1. The chlorophyll a-normalized (or cell-normalized) production rates of VSLs increased with increasing light intensity, e.g., the maximum of chlorophyll a-normalized production rates of CHCl₃ under light intensities of 30, 60 and 120 µmol photons m^− 2 s^− 1 were 0.06, 0.46 and 1.84 µmol (g chlorophyll a) ⁻¹ day^− 1, respectively. Our results suggest that marine diatoms are one of the significant sources of VSLs and that light intensity is a significant factor in estimating VSLs emissions from the open ocean.

In this study we present the seasonal chemical characteristics and potential sources of PM₁₀ at an urban location of Delhi, India during 2010˗2019. The concentrations of carbonaceous aerosols [organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC) and water insoluble organic carbon (WIOC)] and elements (Al, Fe, Ti, Cu, Zn, Mn, Pb, Cr, F, Cl, Br, P, S, K, As, Na, Mg, Ca, B, Ni, Mo, V, Sr, Zr and Rb) in PM₁₀ were estimated to explore their possible sources. The annual average concentration (2010–2019) of PM₁₀ was computed as 227 ± 97 µg m⁻³ with a range of 34˗734 µg m⁻³. The total carbonaceous aerosols in PM₁₀ was accounted for 22.5% of PM₁₀ mass concentration, whereas elements contribution to PM₁₀ was estimated to be 17% of PM₁₀. The statistical analysis of OC vs. EC and OC vs. WSOC of PM₁₀ reveals their common sources (biomass burning and/or fossil fuel combustion) during all the seasons. Enrichment factors (EFs) of the elements and the relationship of Al with other crustal metals (Fe, Ca, Mg and Ti) of PM₁₀ indicates the abundance of mineral dust over Delhi. Principal component analysis (PCA) extracted the five major sources [industrial emission (IE), biomass burning + fossil fuel combustion (BB + FFC), soil dust, vehicular emissions (VE) and sodium and magnesium salts (SMS)] of PM₁₀ in Delhi, India. Back trajectory and cluster analysis of airmass parcel indicate that the pollutants approaching to Delhi are mainly from Pakistan, IGP region, Arabian Sea and Bay of Bengal.

The Cl/OH initiated temperature dependent photo-oxidative reaction kinetics of methyl butyrate (MB) were examined using a relative rate (RR) technique. Gas chromatography with flame ionization and mass spectrometric detection were used to monitor the concentration of the reactants and to identify the products. The temperature dependent kinetics of MB with Cl atoms were measured with respect to the reaction of Cl with C₂H ₆ and C₂H₄. The temperature dependent kinetics for the reaction of MB with OH radicals were measured using n- propanol and iso -propanol as references. The obtained rate coefficients for the Cl and OH reactions with MB are, k Cl(Expt) (T) = [(7.76 ± 0.47) × 10 ⁻¹¹] exp [(10.31 ± 0.20)/T] cm³ molecule⁻¹ s⁻¹ and k OH(Expt) (T) = [(4.32 ± 0.21) × 10 ⁻¹²] exp [-(25.26 ± 0.39)/T] cm³ molecule⁻¹ s⁻¹ respectively. Dual level direct dynamics were used to perform the computational calculations to further elucidate the mechanisms over the studied temperature range. The rate coefficients for H-abstraction reactions were computed using Canonical Variational Transition State Theory with Small Curvature Tunneling (CVT/SCT) with Interpolated Single Point Energies (ISPE) method. The rate coefficients over the studied temperature range yielded the Arrhenius equations: k Cl(Theory) (200–400 K) = [(4.05 ± 0.54) × 10^–11] exp [-(2.80 ± 0.11)/T] cm³ molecule⁻¹ s⁻¹ and k OH(Theory) (200–400 K) = [(1.96 ± 0.68) × 10 -11] exp [-(384 ± 38)/T] cm³ molecule ⁻¹ s ⁻¹. Possible degradation mechanisms for the reactions are proposed based on the observed products. Thermo-chemical parameters, ozone formation potential, branching ratios, and the atmospheric lifetime of MB are calculated to understand the fate of MB in the atmosphere.

In this work, isotopic effects of carbonyls were evaluated during the simulation sampling of gaseous carbonyls by using a carbon isotope method developed, and then variation characteristics of carbon isotopic compositions were investigated for three dominant carbonyls including formaldehyde, acetaldehyde and acetone in the roadside air of Nanning for the first time. A small difference in δ¹³C values (0.04 to 0.50 ‰) were observed between the calculated and measured values of carbonyl-derivatives, indicating that the effect on carbon isotopic fractionation could hardly occurred in the simulation sampling of gaseous carbonyls. The roadside air measurements showed that ({delta }^{13})C values of formaldehyde, acetaldehyde and acetone were –36.02 ‰ to –31.18 ‰, –35.35 ‰ to –32.01 ‰ and –30.45 ‰ to –29.09 ‰, respectively. Further correlation of the measured ({delta }^{13})C values was good for formaldehyde, acetaldehyde and acetone (R² = 0.6275–0.7755), indicating that their similar sources could be the direct vehicular emission or indirect productions from precursors such as hydrocarbons. Particularly, formaldehyde, acetaldehyde and acetone in the roadside air were all enriched in the early afternoon by round 0.5–6 ‰ in ¹³C compared to other sampling durations, which was likely due to the contributions from the positive photo-oxidation productions of hydrocarbons. Finally, it was found that all measured ({delta }^{13})C values (–36.5 ‰ to –29.0 ‰) agreed with the forecasted ({delta }^{13})C range (–43.0 ‰ to –26.0 ‰) according to the ¹³C mass balance of carbonyls and their precursors such as hydrocarbons, indirectly confirming such positive productions in the roadside air.

In this study, the aerosol removal coefficients based on ⁷Be, ²¹⁰Pb and ²¹⁰Po radionuclides in the urban air, in Lodz, Poland, were investigated over 3 years, between May 2014 and December 2017. Results representing the summer/warm and winter/cold seasons were applied to quantity and quality estimates of aerosol removal processes. The values for the removal processes were closely dependent on the meteorological conditions; therefore, a set of nine meteorological parameters was employed in the analysis. The multiple regression method was applied to explain the relationship between the removal coefficients of aerosols and independent factors identified using Principal Component Analysis.

The seasonal variation of particulate matter and its relationship with meteorological parameters were measured at five different residential sites in Delhi. Sampling was carried out for one year including all three seasons (summer, monsoon, and winter). The yearly average concentration of particulate matter (PM_2.5) was 135.16 ± 41.34 µg/m³. The highest average values were observed in winter (208.44 ± 43.67 µg/m³) and the lowest during monsoon season (80.29 ± 39.47 µg/m³). The annual average concentration of PM_2.5 was found to be the highest at the Mukherjee Nagar site (242.16 µg/m³ ) during the winter and lowest at (Jawaharlal Nehru University) JNU (35.65 µg/m³) during the monsoon season. The strongest correlation between PM mass and a meteorological parameter was a strong negative correlation with temperature (R2=0.55). All other parameters were weakly correlated (R2<0.2) with PM mass.

Observations of particulate matter less than 10 µm (PM₁₀) were conducted from January to December in 2015 in the Ciuc basin, Eastern Carpathians, Romania. Daily concentrations of PM₁₀ ranged from 10.90 to 167.70 µg/m³, with an annual mean concentration of 46.31 µg/m³, which is higher than the European Union limit of 40 µg/m³. Samples were analyzed for a total of 21 elements. O, C and Si were the most abundant elements accounting for about 85% of the PM₁₀ mass. Source identification showed that the elemental composition of PM₁₀ is represented by post volcanic activity, crustal origin, and anthropogenic sources, caused by the resuspension of crustal material, sea salt and soil dust. The average PM₁₀ composition was 72.10% soil, 20.92% smoke K, 13.84% salt, 1.53% sulfate and 1.02% organic matter. The back-trajectory analysis showed that the majority of PM₁₀ pollution comes from the West, Southwest and South.

Pre and Post-Monsoon levels of ambient SO₂, NO₂, PM_2.5 and the trace metals Fe, Cu, etc. were measured at industrial and residential regions of the Kochi urban area in South India for a period of two years. The mean PM_2.5, SO₂ and NO₂ concentrations across all sites were 38.98 ± 1.38 µg/m³, 2.78 ± 0.85 µg/m³ and 11.90 ± 4.68 µg/m³ respectively, which is lower than many other Indian cities. There was little difference in any on the measured species between the seasons. A few sites exceeded the NAAQS (define acronym and state standard) and most of the sites exceeded WHO (define acronym and state standard) standard for PM_2.5. The average trace metal concentrations (ng/m³) were found to be Fe (32.58) > Zn (31.93) > Ni (10.13) > Cr (5.48) > Pb (5.37) > Cu (3.24). The maximum concentration of trace metals except Pb were reported in industrial areas. The enrichment factor, of metals relative to crustal material, indicated anthropogenic dominance over natural sources for the trace metal concentration in Kochi’s atmosphere. This work demonstrates the importance of air quality monitoring in this area.

Black carbon (BC) along with PM_2.5 (fine particular matters) plays an important role in the assessment health effect of human beings. Winter season campaign measurements carried out for BC concentrations by using 7 different wavelengths such as 370, 470, 520, 590, 660, 880, and 950 nm, handy aethalometer (AE-33, Magee Scientific, USA), at two different locations i.e., National Institute of Technology, Jamshedpur (NIT J) and Sakchi, Jamshedpur (SAK J), in eastern India. During the study period, the mass concentration of BC varies from 4.19 µgm⁻³ to 15.36 µgm⁻³, with an average mean of 8.88 ± 2.40 µgm⁻³ in NIT J and SAK J, the mass concentration of BC varies from 6.3 µgm⁻³ to 13.48 µgm⁻³, with an average mean of 10.29 ± 1.58 µgm⁻³. However, the concentration of PM_2.5 varies from 102.98 µgm⁻³to 198.21 µgm⁻³, with an average mean of 155.82 ± 29.98 µgm⁻³ in NIT J and SAK J, the concentration of PM_2.5 varies from 110.83 µgm⁻³ to 207.65 µgm⁻³, with an average mean of 169.14 ± 22.40 µgm⁻³. It was reported that SAK J has a higher BC concentration compared to NIT J. This was due to heavy traffic load and dense population in SAK J. Backward Trajectories were seen that the airborne particulate matter came from differerajeshnt directions. According to the diagnostic ratio analysis of BC, it was observed that most of the BC mass concentrations come from fossil-fuel (69.70%) followed by wood-burning (30.30%) in a particular place. The overall health risk assessment of BC concentration observed during the study period was 26.70, 13.95, 24.95 and 51.32 at NIT J as well as 32.07, 16.72, 29.95 and 61.87 at SAK J, the passive cigarettes comparable concerning the risk of CVM, LC, LBW, and PLEDSC, respectively.

Non-methane volatile organic compounds (NMVOCs) play key roles in local and regional atmospheric chemistry as precursors for the production of ozone and secondary organic aerosols. Ambient air C₂-C₅ NMVOCs were measured at a tropical forest site in the central Western Ghats and urban site of Udaipur in India during the late monsoon period of 2016–17 and 2015, respectively. In the Western Ghats, air samples were collected from the protected Bhagwan Mahaveer Sanctuary. Ethene, propene, and isoprene were the dominant biogenic compounds with mean concentrations of 4.8 ± 2, 1.6 ± 0.66 and 1.05 ± 0.43 ppb, respectively. The concentrations of anthropogenic compounds such as propane and pentane were significantly lower than those of light alkenes. The contributions of ethene and propene among different NMVOCs were ~ 44 and 14%, respectively. However, the contributions of isoprene were highly variable of 3–22%. The tight correlation (r² = 0.90) between the mixing ratios of ethene and propene and their ratio indicates their common formation and emission mechanisms. The molar emission ratio of ethene/propene (2.9 ± 0.17 ppb ppb⁻¹) was comparable to those measured at other biogenic sites of Asia while higher than those reported for mid-latitude sites. The concentrations of light alkenes and isoprene at the Western Ghats were 4–5 times higher than those measured in an urban environment in the same season. The higher ozone formation potentials and Propylene-Equivalent concentrations of alkenes and isoprene than those of other NMVOCs indicate important implications of biogenic emissions on ozone photochemistry in the forest regions of India.

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