Journal of Atmospheric Chemistry最新文献

Aerosol acidity is found to exert negative effects on ecosystem diversity and architectural appearance. Current analytical technology is unable to measure in-situ aerosol acidity (i.e., pH value) of ambient fine particle due to the absence of appropriate pH electrodes. Thermodynamic modeling methods including ISORROPIA II and Extended Aerosol Inorganics Model Version IV (E-AIM V) are mostly used in the estimation of in-situ aerosol acidity with the inputs of water soluble ions worldwide. This study proposes a flexible method with the aid of multilayer perceptron (MLP) neural network analysis to estimate in-situ aerosol acidity of ambient fine particle (< 2.5 μm in aerodynamic diameter or PM_2.5) with the inputs of water soluble ions (i.e., Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺), gaseous air pollutants (i.e., CO, NO₂, SO₂) and meteorological parameters (i.e., humidity and temperature). The dataset consists of ambient fine particles collected across four individual sampling periods in the autumn and winter of 2019 and 2020 at a suburban site of Nanjing. The pH values of ambient fine particle were found to be ranging from 2.0 to 4.0 estimated by E-AIM model. Levels of pH estimated by MLP neural network analysis agreed well with pH values estimated by E-AIM model with R² value of 0.98.

Rapid transport by deep convection is an important mechanism for delivering surface emissions of reactive halocarbons and other trace species to the tropical tropopause layer (TTL), a key region of transport to the stratosphere. Recent model studies have indicated that increased delivery of short-lived halocarbons to the TTL could delay stratospheric ozone recovery. We report here measurements in the TTL over the western Pacific Ocean of short-lived halocarbons and other trace gases that were transported eastward after convective lofting over Asia. Back-trajectories indicate the sampled air primarily originated from the Indian subcontinent. While short-lived organic bromine species show no measurable change over background mixing ratios, short-lived chlorinated organic species were elevated above background mixing ratios (dichloromethane (Δ48.2 ppt), 1,2-dichloroethane (Δ4.21 ppt), and chloroform (Δ4.85 ppt)), as well as longer-lived halogenated species, methyl chloride (Δ82.0 ppt) and methyl bromide (Δ1.91 ppt). This transported air mass thus contributed an excess equivalent effective chlorine burden of 316 ppt, with 119 ppt from short lived chlorinated species, to the TTL. Non-methane hydrocarbons (NMHC) were elevated 60 - 400% above background mixing ratios. The NMHC measurements were used to characterize the potential source regions, which are consistent with the convective influence analysis. The measurements indicate a chemical composition heavily impacted by biofuel/biomass burning and industrial emissions. This work shows that convection can loft Asian emissions, including short-lived chlorocarbons, and transport them to the remote TTL.

This study presents the chemical composition (carbonaceous and nitrogenous components) of aerosols (PM_2.5 and PM₁₀) along with stable isotopic composition (δ¹³C and δ¹⁵N) collected during winter and the summer months of 2015–16 to explore the possible sources of aerosols in megacity Delhi, India. The mean concentrations (mean ± standard deviation at 1σ) of PM_2.5 and PM₁₀ were 223 ± 69 µg m⁻³ and 328 ± 65 µg m⁻³, respectively during winter season whereas the mean concentrations of PM_2.5 and PM₁₀ were 147 ± 22 µg m⁻³ and 236 ± 61 µg m⁻³, respectively during summer season. The mean value of δ¹³C (range: − 26.4 to − 23.4‰) and δ¹⁵N (range: 3.3 to 14.4‰) of PM_2.5 were − 25.3 ± 0.5‰ and 8.9 ± 2.1‰, respectively during winter season whereas the mean value of δ¹³C (range: − 26.7 to − 25.3‰) and δ¹⁵N (range: 2.8 to 11.5‰) of PM_2.5 were − 26.1 ± 0.4‰ and 6.4 ± 2.5‰, respectively during the summer season. Comparison of stable C and N isotopic fingerprints of major identical sources suggested that major portion of PM_2.5 and PM₁₀ at Delhi were mainly from fossil fuel combustion (FFC), biomass burning (BB) (C-3 and C-4 type vegitation), secondary aerosols (SAs) and road dust (SD). The correlation analysis of δ¹³C with other C (OC, TC, OC/EC and OC/WSOC) components and δ¹⁵N with other N components (TN, NH₄⁺ and NO₃⁻) are also support the source identification of isotopic signatures.

At the pandemic of COVID-19, the movement of business and other non-essential activities were majorly restricted at the end of March 2020 in India and continued in different lockdown phases until June 2020. By categorically, studying sensitivity towards anthropogenic factors with other environmental implications in urban Indian cities during phase-wise lockdown scenarios will pave the way for a refined Clean Air Programme (CAP). In this study, the aerosol particulate matter variations between the lockdown phases in both spatial and temporal scales have been explored along with cities exceeding national ambient air quality (NAAQ) standards covering different geographical regions of India for their air quality level. The results of the spatial pattern of Copernicus Atmosphere Monitoring System (CAMS) near-real-time data showed a negative change both in Aerosol Optical Depth (AOD) (-0.2 to 0.1) and black carbon AOD (bcAOD) (-0.9 to -0.75). The changes were evident in successive phases of lockdown with an overall AOD reduction of about 70–90%. Southern urban cities showed a significant impact of mobile sources from temporal analysis than other cities. Principal Component Analysis (PCA) for effects of pollutants by anthropogenic factors (mobile and point source) and meteorological factors (wind speed, wind direction, solar radiation, relative humidity) revealed the two significant driving factors. PM reduction was about 50–70%, predominantly due to anthropogenic factors. The factor analysis revealed the influence of meteorological factors between the major urban cities (Delhi, Kolkata, Mumbai, Chennai, Bengaluru, and Hyderabad). Cities that exceed NAAQ standard performed well during phase-wise lockdowns, exceptional to cities in Gangetic plain. This study helps to frame region-specific strategic action plans for the CAP.

The present study comprehensively reports the simultaneous measurement of wet deposition of total inorganic nitrogen (TIN; which is the sum of the NH₄⁺-N and NO₃⁻-N) at three different sites in Nr emission hotspot of Indo-Gangetic plain (IGP) over a year-long temporal scale from October 2017 to September 2018. At rural Meetli (MTL) site, urban Baraut (BRT) site and industrial Loni (LNI) site, the annual wet deposition of NH₄⁺-N was estimated as 21.87, 19.48 and 7.43 kg N ha⁻¹ yr⁻¹, respectively; the annual wet deposition NO₃⁻-N was estimated as 12.96, 12.17 and 4.44 kg N ha⁻¹ yr⁻¹, respectively; and the annual wet deposition of TIN was estimated as 34.83, 31.64 and 11.87 kg N ha⁻¹ yr⁻¹, respectively. NH₄⁺-N was dominantly contributing species in annual, monsoon and non-monsoon-time wet deposition of TIN at all sites. The spatial gradient (variability) in percent contribution of NH₄⁺ to total annual volume-weighted mean (VWM) concentration of all analyte ions was observed as MTL (43.23%) > BRT (37.90%) > LNI (30%). On the other hand, the spatial gradient in percent contribution of NO₃⁻ to total annual VWM concentration of all analyte ions was observed as MTL (7.45%) > BRT (6.89%) > LNI (5.32%). The extremely narrow range of NH₄⁺-N/NO₃⁻-N ratios (ranging from 1.60 at BRT site to 1.69 at LNI site) showed the approximately equal relative abundance of oxidized and reduced nitrogen (N) deposition across all sites. Inferences from enrichment factor analysis, principal component analysis and Pearson’s correlation coefficient analysis suggested that across all sites, virtually all NH₄⁺-N and NO₃⁻-N depositions were originated anthropogenically. The annual wet deposition of TIN measured in this study showed ≥ 6865%, ≥ 6228% and ≥ 2274% increment than the natural N deposition rate at MTL, BRT and LNI site, respectively. These empirically measured annual wet depositions of TIN also emanated theoretical transgression of critical N load threshold across all sites therefore signifying probable undermining of long-term elastic stability and resilience of ecosystems against stressor in the study domain.

Size-segregated aerosol particles were collected using a high volume MOUDI sampler at a coastal urban site in Xiamen Bay, China, from March 2018 to June 2020 to examine the seasonal characteristics of aerosol and water-soluble inorganic ions (WSIIs) and the dry deposition of nitrogen species. During the study period, the annual average concentrations of PM₁, PM_2.5, PM₁₀, and TSP were 14.8 ± 5.6, 21.1 ± 9.0, 35.4 ± 14.2 μg m⁻³, and 45.2 ± 21.3 μg m⁻³, respectively. The seasonal variations of aerosol concentrations were impacted by the monsoon with the lowest value in summer and the higher values in other seasons. For WSIIs, the annual average concentrations were 6.3 ± 3.3, 2.1 ± 1.2, 3.3 ± 1.5, and 1.6 ± 0.8 μg m⁻³ in PM₁, PM_1-2.5, PM_2.5–10, and PM_>10, respectively. In addition, pronounced seasonal variations of WSIIs in PM₁ and PM_1-2.5 were observed, with the highest concentration in spring-winter and the lowest in summer. The size distribution showed that SO₄²⁻, NH₄⁺ and K⁺ were consistently present in the submicron particles while Ca²⁺, Mg²⁺, Na⁺ and Cl⁻ mainly accumulated in the size range of 2.5–10 μm, reflecting their different dominant sources. In spring, fall and winter, a bimodal distribution of NO₃⁻ was observed with one peak at 2.5–10 μm and another peak at 0.44–1 μm. In summer, however, the fine mode peak disappeared, likely due to the unfavorable conditions for the formation of NH₄NO₃. For NH₄⁺ and SO₄²⁻, their dominant peak at 0.25–0.44 μm in summer and fall shifted to 0.44–1 μm in spring and winter. Although the concentration of NO₃–N was lower than NH₄–N, the dry deposition flux of NO₃–N (35.77 ± 24.49 μmol N m⁻² d⁻¹) was much higher than that of NH₄–N (10.95 ± 11.89 μmol N m⁻² d⁻¹), mainly due to the larger deposition velocities of NO₃–N. The contribution of sea-salt particles to the total particulate inorganic N deposition was estimated to be 23.9—52.8%. Dry deposition of particulate inorganic N accounted for 0.95% of other terrestrial N influxes. The annual total N deposition can create a new productivity of 3.55 mgC m⁻² d⁻¹, accounting for 1.3–4.7% of the primary productivity in Xiamen Bay. In light of these results, atmospheric N deposition could have a significant influence on biogeochemistry cycle of nutrients with respect to projected increase of anthropogenic emissions from mobile sources in coastal region.

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.