Journal of Atmospheric Chemistry

Current research reports and chronological list of recent articles.


The international scientific Journal of Atmospheric Chemistry is devoted to the study of the chemistry of the atmosphere, with particular emphasis on the region below about 100 km. The strongly interdisciplinary nature of atmospheric chemistry means that it embraces a great variety of sciences.

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Journal of Atmospheric Chemistry - Abstracts



A new continuous measurement method for gaseous ammonia by counter-current flow tube sampling and indophenol reaction

Abstract

Ammonia (NH3) is the most abundant alkaline gas in the atmosphere and plays a key role in atmospheric chemistry. Reliable and high-time-resolution data for gaseous ammonia are necessary to understand the sources and sinks of ammonia gas in ambient air. In the present study, a sensitive and continuous instrument for measuring gaseous ammonia was developed. Ammonia gas in ambient air was collected in an aqueous solution using a counter-current flow tube (CCFT) sampler. Then, ammonium formed in the aqueous solution was detected by the indophenol method. Based on a CCFT length of 50 cm and air flow rate of 1 L/min, the collection efficiency exceeded 98.5 % at an ammonia mixing ratio of up to 120 ppbv. The detection limit of this method was 0.062 ppbv. Interferences from several gases were investigated, and the results showed that the present method was not affected by NOx, O3, SO2, HONO, methylamine, formaldehyde, hydrogen sulfide or a mixture of these gases. The most important result was that only gaseous ammonia was detected in the present method without any interference from the particulate ammonium in ambient air. Comparisons with data based on the dry denuder method indicated that the present method showed good agreement with the denuder method.


Datum: 01.09.2016


Multi-species chemical data assimilation with the Danish Eulerian hemispheric model: system description and verification

Abstract

Satellite retrievals of atmospheric composition provide a wealth of data on a global scale. These complement results from atmospheric chemistry-transport models (CTMs), and can be combined using data assimilation. We present two assimilation schemes coupled to the Danish Eulerian Hemispheric Model (DEHM), a three-dimensional, off-line CTM with full photochemistry: a variant on the ensemble Kalman filter and the three-dimensional variational scheme. The aim of this paper is to describe the two schemes and present an initial assessment of their impacts on model skill. Retrievals of multiple atmospheric trace gases are assimilated, namely: NO2 tropospheric column densities, CH4 total column densities, and partial column concentrations of O3, CO and CH4; these data are retrieved from four satellite sensors. Data for each species are assimilated independently of one another, and other species are only adjusted indirectly via the model’s chemistry and dynamics. Assimilation results are compared with measurements from surface monitoring stations and other satellite retrievals, and preliminary validation results are presented.Reference simulations (without assimilation) grossly underestimate surface CO concentrations, and both assimilation schemes eliminate this large and systematic model bias. The assimilation improves the spatial correlation of modelled CO with surface observations, and improves the spatial correlation between forecasts and retrievals for CO, NO2 and O3. Results for CH4 show a loss of skill due to a mismatch in model bias between two assimilated CH4 data-sets. Finally, we discuss differences in methodology and results between this paper and a recent study on multi-species chemical data assimilation. Joint optimisation of initial conditions and emission rates offers a promising direction for improving modelled boundary-layer concentrations.


Datum: 01.09.2016


A study on the precipitation in Izmir, Turkey: chemical composition and source apportionment by receptor models

Abstract

The chemistry of rainwater was studied in three sites of a metropolitan city of Turkey to determine the spatial variation, sources affecting composition and the extent of their influence. The acidity of rainwater, Ca, Co, Cr, Zn, Ba, V and Ni showed significant spatial variations. The most of measured species were moderately to extremely enriched compared to the local soil, which is likely arisen from the anthropogenic activities. SO4 2−, K and Ca were found to be predominantly non-sea origin. Two receptor models, Positive Matrix Factorization (PMF) and Chemical Mass Balance (CMB), agreed well on the source contribution estimations of Al, K, Zn, V, Pb and Cr. The PMF and CMB resolved very similar source contribution profiles to the elemental concentrations of Ca, Zn, V, Pb, K and Na, which the majority of those resulted from mineral industries, bell casting+steel industries, fossil fuel burning, biomass burning+sea salt and sea salt, respectively. The PMF resolved the source contributions of long-transported emissions, particularly for Ba, Sr and Mn, which could not be estimated by the CMB.


Datum: 01.09.2016


Mass spectrometric study of aged benzene secondary organic aerosol in the presence of dry ammonium sulfate

Abstract

Inorganic seed particles have relatively large surface area, and play an important role in the formation and aging of secondary organic aerosol (SOA). The effects of dry (NH4)2SO4 which is the most commonly found in urban atmosphere on the aged benzene SOA were qualitatively studied utilizing aerosol laser time-of-flight mass spectrometer (ALTOFMS) coupled with Fuzzy C-Means (FCM) clustering algorithm in this study. Experimental results indicated that nitrophenol, oxocarboxylic acid, epoxide products are the predominant components in the aged benzene SOA in the presence of low concentration (about 10 μg m−3) of dry (NH4)2SO4. These aged products are the same as the previously obtained aged benzene SOA without (NH4)2SO4 seed aerosol, indicating that low concentration of dry (NH4)2SO4 acts just as the nucleation or condensation center of the SOA, and do not affect the chemical composition of SOA. However, 1 H-imidazole, 1 H-imidazole-2-carbaldehyde, hydrated 1 H-imidazole-2-carbaldehyde, 2,2′-biimidazole, hydrated N-glyoxal substituted 1 H-imidazole, N-glyoxal substituted hydrated 1 H-imidazole-2- carbaldehyde, hydrated mono glyoxal substituted hydrated 1 H-imidazole-2-carboxaldehyde, mono glyoxal substituted 2,2-biimidazole and hydrated glyoxal dimer substituted imidazole which are formed from ammonium ion reaction with glyoxal are the major particulate products in the aged benzene SOA in the presence of high concentration (about 100 μg m−3) of dry (NH4)2SO4. The retention of water on the dry (NH4)2SO4 particles creates ammonium ion, which can promote the formation of high-molecular-weight (HMW) products through multiphase reactions such as hydration and polymerization of aldehydes form from OH-initiated oxidation of benzene.


Datum: 01.09.2016


Dimethyl sulfide and other biogenic volatile organic compound emissions from branching coral and reef seawater: potential sources of secondary aerosol over the Great Barrier Reef

Abstract

Volatile organic compounds (VOCs) in the headspace of bubble chambers containing branches of live coral in filtered reef seawater were analysed using gas chromatography with mass spectrometry (GC-MS). When the coral released mucus it was a source of dimethyl sulfide (DMS) and isoprene; however, these VOCs were not emitted to the chamber headspace from mucus-free coral. This finding, which suggests that coral is an intermittent source of DMS and isoprene, was supported by the observation of occasional large pulses of atmospheric DMS (DMSa) over Heron Island reef on the southern Great Barrier Reef (GBR), Australia, in the austral winter. The highest DMSa pulse (320 ppt) was three orders of magnitude less than the DMS mixing ratio (460 ppb) measured in the headspace of a dynamically purged bubble chamber containing a mucus-coated branch of Acropora aspera indicating that coral reefs can be strong point sources of DMSa. Static headspace GC-MS analysis of coral fragments identified mainly DMS and seven other minor reduced sulfur compounds including dimethyl disulfide, methyl mercaptan, and carbon disulfide, while coral reef seawater was an indicated source of methylene chloride, acetone, and methyl ethyl ketone. The VOCs emitted by coral and reef seawater are capable of producing new atmospheric particles < 15 nm diameter as observed at Heron Island reef. DMS and isoprene are known to play a role in low-level cloud formation, so aerosol precursors such as these could influence regional climate through a sea surface temperature regulation mechanism hypothesized to operate over the GBR.


Datum: 01.09.2016


Uptake of nitrogen dioxide (NO 2 ) on acidic aqueous humic acid (HA) solutions as a missing daytime nitrous acid (HONO) surface source

Abstract

A comprehensive kinetic study of a potential daytime nitrous acid (HONO) source reaction, the photoenhanced reduction reaction of the nitrogen dioxide (NO2) on acidic humic acid (HA), was completed using a wetted-wall flow tube (WWFT) (Fickert et al.: J. Phys. Chem. A. 102, 10689, 1998) photoreactor integrated with a high sensitivity HONO analyser (Wall et al.: J. Atmos. Chem. 55, 31–54, 2006; Huang et al.: Atmos. Environ. 36, 2225–2235, 2002). The nature of this reaction, is of great interest since recently observed, unpredictably high HONO daytime concentrations demand its ordinarily proposed heterogeneous source to proceed 60 times more rapidly at noon than during the night (Kleffmann et al.: ChemPhysChem 8, 1137–1144, 2007). This study investigated the nature of the reduction reaction with simulated colloidal HA aqueous solutions characteristic of anaerobic environmental conditions, varying in acidity, concentration and composition. Typical urban NO2 levels were investigated. Increasing photoenhanced HONO production with weakening solution acidity was detected due to increased deprotonation of the carboxyl groups within the humic acid. It was deduced that the acidic HA substrate contains numerous feasible chromophoric sensitizer units capable of photochemically reducing NO2 to HONO, owing to its ‘biofilm’ (Donlan, 2002) function under UV exposure. The mechanism was found to be more effective for HA standards with higher levels of ‘bioactivity’ (refractivity). Using a complex mathematical model developed, incorporating both chemistry and diffusion, reaction probability datasets were produced from the experimental data, providing evidence that this is, indeed, an environmentally important daytime HONO surface source reaction. The parameters required to scale up the data of the photoreactor to that of a regional rural/urban scale were assessed.


Datum: 12.08.2016


Rainwater chemistry and bulk atmospheric deposition in a tropical semiarid ecosystem: the Brazilian Caatinga

Abstract

We assessed the rainwater chemistry, the potential sources of its main inorganic components and bulk atmospheric deposition in a rural tropical semiarid region in the Brazilian Caatinga. Rainfall samples were collected during two wet seasons, one during an extremely dry year (2012) and one during a year with normal rainfall (2013). According to measurements of the main inorganic ions in the rainwater (H+, Na+, NH4 +, K+, Ca2+, Mg2+, Cl, NO3 , and SO4 2−), no differences were observed in the total ionic charge between the two investigated wet seasons. However, Ca2+, K+, NH4 + and NO3 were significant higher in the wetter year (p < 0.05) which was attributed to anthropogenic activities, such as organic fertilizer applications. The total ionic contents of the rainwater suggested a dominant marine contribution, accounting for 76 % and 58 % of the rainwater in 2012 and 2013, respectively. The sum of the non-sea-salt fractions of Cl, SO4 2−, Mg2+, Ca2+ and K+ were 19 % and 33 % in 2012 and 2013, and the nitrogenous compounds accounted for 2.8 % and 6.0 % of the total ionic contents in 2012 and 2013, respectively. The ionic ratios suggested that Mg2+ was probably the main neutralizing constituent of rainwater acidity, followed by Ca2+. We observed a low bulk atmospheric deposition of all major rainwater ions during both wet seasons. Regarding nitrogen deposition, we estimated slightly lower annual inputs than previous global estimates. Our findings contribute to the understanding of rainfall chemistry in northeastern Brazil by providing baseline information for a previously unstudied tropical semiarid ecosystem.


Datum: 28.06.2016


Characterisation of water-soluble organic aerosols at a site on the southwest coast of India

Abstract

Aerosol samples collected over a tropical location, Thumba, southernmost West Coast of India were analyzed for the abundance of homologous dicarboxylic acids (C2 to C12), oxocarboxylic acids (ωC2 to ωC9, pyruvic acid), α-dicarbonyls (glyoxal and methylglyoxal), organic and elemental carbon. Among the measured organics, oxalic acid was found to be the most abundant species followed by succinic and/or malonic acids. As oxoacid and α-carbonyl groups, glyoxylic acid and glyoxal, respectively, were observed to be dominant. On average, dicarboxylic acids accounted almost 2.1 ± 0.7 % of the aerosol total organic carbon. Among the aerosols over Thumba, two types of formation pathways were noticed for oxalic acid. During the post-monsoon and winter periods, the photo-oxidation of biogenic and anthropogenic volatile organic compounds lead to the formation of oxalic acid through a chain reaction involving glyoxal, methylglyoxal, pyruvic and glyoxylic acids. In contrast, during the pre-monsoon, the oxidative degradation of the biogenic unsaturated fatty acids give rise to succinic acid, which can be decomposed to malonic acid and then to oxalic acid. The observed seasonal variations in acid concentrations are consistent with photochemical production and the subsequent accumulation under favourable meteorological conditions prevailing over the region.


Datum: 01.06.2016


Carbon isotopic ( 14 C and 13 C) characterization of fossil-fuel derived dissolved organic carbon in wet precipitation in Shandong Province, China

Abstract

We present results from a 1-year study of radiocarbon and stable carbon isotope measurement of dissolved organic carbon (DOC) of wet precipitation samples collected in the Shandong province of China. A total of 32 rainfall and 4 snow samples were collected from two coastal cities (Qingdao and Yantai) and one inland site (Taian) during 2014. Concentrations of DOC in the rainwater and snow samples varied widely from 28 to 616 μM. In general, rainwater originating from marine sources had relatively low DOC concentrations compared with continentally generated precipitation. Values of δ13C-DOC and Δ14C-DOC in the snow and rainwater ranged from −19.0 to −29.4 ‰ and −23 to −494 ‰, with corresponding radiocarbon ages of 125 to 5410 years before present. The dominant DOC in the wet precipitation had a relatively old 14C age (average 2841 years) and a depleted 13C value (average −24.4 ‰), indicating the mixing of contemporary organic carbon with 14C-depleted fossil fuel-derived soluble organic carbon in the atmosphere. Using a dual isotopic two-endmember model, we calculate that 7 % to 52 % of DOC in the snow and rainfall originated from fossil fuels. It is estimated that the flux of DOC in continental rainfall of China is 23 × 1012 g C yr−1 and of this, 7.1 × 1012 g C yr−1 could be fossil-fuel OC. On a global scale, the DOC flux in rainfall is estimated to be 357 Tg C yr−1, and 110 Tg C yr−1 could be fossil fuel-derived. Our study demonstrates that wet precipitation is an important removal process for old fossil fuel carbon from the atmosphere. This removal mechanism could play an important role in the carbon cycle, especially for the anthropogenically derived fraction, and it should be taken into consideration in global carbon cycle models.


Datum: 01.06.2016


Particulate morphology and elemental characteristics: variability at middle Indo-Gangetic Plain

Abstract

Airborne particulates were monitored at an urban location of middle Indo-Gangetic Plain (IGP) and subsequently analyzed for particulate diversity and mixing states. Exceptionally high particulate loadings were found both in case of coarser (PM10: 157.5 ± 102.9 μgm−3, n = 46) and finer particulates (PM2.5: 92.5 ± 49.8 μgm−3). Based on particulate morphology and elemental composition, five different clusters of particulates namely tarball, soot, sulphur-rich, aluminosilicate and mineral species were found to dominate. Soot particles (0.1–5 μm) were found to be partly coated, having voids filled by coating material without being completely engulfed. A specific type of amorphous, carbonaceous spherules was evident in wintertime fine particulates signifying emissions from biomass burning and wild fire. Traces of S, Na and Ca were found associated with carbonaceous agglomerates suggesting its metal scavenging behavior. Particle laden filters were further processed for metallic and water soluble ionic species to constitute aerosol composition. Coarser particulates were characterized with higher metallic species (9.2–17.8 %), mostly of crustal origin (Ca: 5.5 %; Fe: 1.6 %; Zn: 1.3 % and Na: 3.8 %) while PM2.5 also revealed their association with metallic components (6.0–14.9 %) having Ca (4.6 %), Fe (0.9 %) and K (0.8 %) as principle constituents. Ca, Na and NH4 + found to generate chloride and sulphate salts thus affecting particulate hygroscopicity. Elevated fractions of NO3 and K+ in PM2.5 signified contribution of biomass burning while presence of Cl with carbonaceous aerosols having traces of Si and K denoted contribution of farming and burning practices. Black carbon aerosol exhibited significant seasonal variability (6.9−21.9 μgm−3) which support larger association of carbonaceous aerosols in particle micrograph.


Datum: 01.06.2016


Optical properties and chemical apportionment of summertime PM 2.5 in the suburb of Nanjing

Abstract

A field measurement of aerosol optical properties and chemical composition was carried out from August 25, 2012 to September 6, 2012 in Nanjing, China. A three-wavelength Photo-Acoustic Soot Spectrometer (PASS-3) was used to measure aerosol scattering and absorption coefficient (B sca and B abs ) with the wavelength dependent (405, 532, 781 nm). Samples were also collected by a Particle into Liquid Sampler (PILS) with a time resolution of 1 hour and water soluble chemical composition was analyzed by ion chromatography (IC). The hourly average B sca were 239.9 ± 115.3, 185.9 ± 99.3 and 93.8 ± 59.8 Mm−1 while the average B abs were 33.5 ± 21.8, 23.9 ± 15.7 and 16.7 ± 11.7 Mm−1 for 405, 532 and 781 nm. The air mass from Shandong province to Northwest of Nanjing (SN) brought rich chemical composition which can enhance aerosol optical properties. The largest B sca (~389.9, 321.9, 180.5 Mm−1), B abs (~59.7, 43.0, 31.0 Mm−1), ω532 (~0.89) and lowest visibility (~3.2Km), Å sca (405/781) (~1.19) were observed during SN period. The mass concentrations of organic carbon (OC), elemental carbon (EC) and water soluble inorganic ions (NH4 +, K+, NO3 , and SO4 2−) also continued to increase. However, aerosol optical properties and chemical composition kept stable for the episode with the air mass from Oceanic Regions (OR). Ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), organic mass (OM), elemental carbon (EC), fine soil (FS) and sea salt (SS) contributed 49.1, 4.0, 31.6, 9.3, 5.9, and 0.1 % to the total extinction coefficient in summer. (NH4)2SO4, OM and EC were dominant chemical components and the total contribution of them reached to 90 % of the dry aerosol extinction. The proportion of (NH4)2SO4 increased whereas OM and EC showed a decrease during SN period. Our study indicated that the summertime aerosol pollution at the northern suburb of Nanjing was mainly attributed to agricultural biomass burning and secondary aerosol formation. The long-range transport plays an important role in the formation of haze episodes in summertime of Nanjing.


Datum: 01.06.2016


Toxic volatile organic air pollutants across Canada: multi-year concentration trends, regional air quality modelling and source apportionment

Abstract

A Unified Regional Air-quality Modelling System, AURAMS, was expanded to predict six toxic volatile organic compounds (VOCs) within a continental domain and two nested domains covering eastern and western Canada. The model predictions were evaluated against Environment Canada’s National Air Pollution Surveillance (NAPS) data set to assess the predictive capability of the model at daily and seasonal time scales. The predictions were also evaluated with satellite-derived column total maps for formaldehyde, carbon monoxide, and nitrogen dioxide. In general, the model showed fair to good predictive skill in terms of both correlation (R) and normalized mean bias (NMB) for benzene (R = 0.53 NMB = 26 %), formaldehyde (R = 0.73, NMB = −15 %) and acetaldehyde (R = 0.55, NMB = 29 %). For the other toxics VOCs, the model showed less predictive skill in the order 1,2,4-trimethylbenzene (R = 0.50, NMB = −41 %), 1,3-butadiene (R = 0.26, NMB = 40 %) and acrolein (R = 0.052, NMB = −51 %). The goal of this study was to apply an air quality model to assess the contribution of mobile sources to ambient levels of toxic VOCs at urban locations across Canada. The mobile source contribution varied in a complex manner for each species for different regions. For benzene and 1,2,4-trimethylbenzene, the mobile source contribution was in the range 40–65 % for major Canadian cities. The model predicted considerably lower mobile source contributions for rural locations in the Canadian Prairies, where other area sources dominate, such as the petrochemical industry. Measured concentration trends in toxics are also presented from 2004 to 2010. The primary emitted toxics declined gradually (13–16 % over 6 yr) whereas the toxic aldehydes showed no trend.


Datum: 01.06.2016


Depositional ice nucleation on NX illite and mixtures of NX illite with organic acids

Abstract

Mineral dust particles are known to be efficient ice nuclei in the atmosphere. Previous work has probed heterogeneous ice nucleation on various laboratory dust samples including Arizona Test Dust, kaolinite, montmorillonite, and illite as atmospheric dust surrogates. However, it has recently been suggested that NX illite may be a better representation of atmospheric dust. Hiranuma et al. (2015) performed a laboratory comparison for immersion ice nucleation on NX illite, but here we focus on depositional ice nucleation because of its importance in low temperature cirrus cloud formation. A Raman microscope setup was used to examine the ice-nucleating efficiency of NX illite. Organic coatings on the NX illite particles were also investigated using a mixture of 5 dicarboxylic acids (M5). The ratio of NX illite to M5 was varied from 1:10 to 100:1. It was found that NX illite efficiently nucleates ice with Sice = 1.07 ± 0.01 at −47 °C, with Sice slightly increasing at lower temperatures. In contrast, pure M5 is a poorer ice nucleus with Sice = 1.30 ± 0.02 at −40 °C, relatively independent of temperature. Further, it was found that M5 coatings on the order of several monolayers thick hindered the ice nucleating ability of NX illite. Optical images suggest that at colder temperatures (< −50 °C) 1:1 NX illite:M5 particles and pure M5 particles nucleate ice depositionally, while at warmer temperatures (> −50 °C) subsaturated immersion ice nucleation dominates. These experiments suggest that mineral dust particles may become less active towards ice nucleation as they age in the atmosphere.


Datum: 28.05.2016


Annual and decadal variation in chemical composition of rain water at all the ten GAW stations in India

Abstract

Spatial variation of long term annual precipitation volume weighted concentrations of major chemical constituents (SO4 −2, NO3 , Cl, NH4 +, Ca+2, Mg+2, Na+ and K+ ) at all the ten Global Atmospheric Watch (GAW) stations in India for the period from 1981 to 2012 is studied in this paper. Ionic abundance and balance is studied as well. The range of long term annual mean pH at ten stations was 5.25 ± 0.82 to 6.91 ± 0.76, lowest at Mohanbari and highest at Jodhpur. The long term annual mean pH for the period 1981–2012 showed decreasing trend at all the stations (significant at 5 % level). Decadal mean pH among ten stations for 1981–1990, 1991–2000 and 2001–2012 ranged between 7.31 to 5.76, 7.45 to 4.92 and 6.16 to 4.77 respectively and showed decreasing trend at all the stations during 1981–1990 to 2001–12. The percentage occurrence of acidic pH (<5.65) at ten stations ranged from 3 to 72 %, lowest at Jodhpur and highest at Mohanbari and it increased from 1981–1990 to 2001–2012 almost at all the stations. Temporal variation of annual mean values of nssSO4 −2, NO3 , Ca+2 and pH for the study period were attempted. Variation of nss K (non sea salt Potassium) at all the stations was studied to assess the biomass burning contribution in different regions. Non-marine (terrestrial) contribution dominated for majority of ionic constituents at most of the stations. However marine contribution was found to be dominant for Mg at Port Blair and Minicoy. Also sea salt fraction of SO4 was higher than terrestrial at Minicoy. Sources of measured ionic constituents in rain water are assessed through correlation analysis. The concentrations of all the ionic species were lowest at Kodaikanal, a high altitude hill top station and the total ionic mass was 136.0 μeq/l. Jodhpur, an arid station not only had highest concentrations of Ca+2, SO4 −2 and K+ but also had highest total ionic content (1051.8 μeq/l) among all the stations. At Srinagar, Jodhpur, Allahabad, Nagpur and Pune stations Ca+2 was the dominant cation while dominant anion was NO3 for Srinagar, Allahabad, and Nagpur and Cl for Jodhpur and Pune; at Mohanbari NO3 and Ca+2; at Visakhapatnam, Port Blair and Minicoy Na+ and Cl were abundant. Temporal variation had shown an increasing trend for nssSO4 −2 and NO3 and obviously decreasing trend for pH at all the stations. However, Ca+2 showed a decreasing trend at all the stations except at Port Blair. With the exception of Pune and Jodhpur stations, nssK showed a decreasing trend at all the stations revealing decreasing influence of soil/biomass burning over Indian GAW stations. Negative correlation of pH with SO4 −2 was found to be weak compared to NO3 .


Datum: 06.05.2016


Inorganic ions and trace metals bulk deposition at an Atlantic Coastal European region

Abstract

The inorganic chemical composition (major ions and trace metals) of bulk deposition samples collected monthly with bulk collectors at seven Atlantic Coastal European cities (Galicia, Northwest of Spain) during wet season (September 2011 to March 2012) has been assessed and compared. Trace metals (Al, As, Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn) were analysed in soluble fraction and non-soluble fraction (after acid extraction) of the bulk deposition by inductively coupled plasma-mass spectrometry. Major inorganic ions (Cl, NO3 , SO4 2−, Na+, K+, Ca2+, Mg2+ and NH4 +) were analysed in the soluble fraction of the bulk deposition by capillary zone electrophoresis. Univariate analysis (ANOVA and Multiple Range Test) according to the location of each sampling site was performed. Results also suggest a great influence of cleaner Atlantic air masses. After partition coefficients and enrichment factor estimation, similar sources could be assigned for the ionic and metal composition of bulk deposition at seven urban sites.


Datum: 04.05.2016


Ionic and elemental composition of PM 2.5 aerosols over the Caribbean Sea in the Tropical Atlantic

Abstract

To characterize atmospheric particulate matter equal or less than 2.5 μm in diameter (PM2.5) over the Tropical Atlantic Ocean, aerosol sampling was carried out in Puerto Rico during August and September, 2006. Aerosols were analyzed by ion chromatography for water-soluble inorganic and organic ions (including Na+, NH4 +, Mg2+, Ca2+, K+, Cl, SO4 2−, NH4 +, F, methanesulfonate (MSA), and oxalate), by inductive coupled plasma mass spectrometry (ICPMS) for trace elements (Al, Fe, Zn, Mn, Cu, Ni, V, Pb, Cr, Sb, Co, Sc, Cd), and by scanning electron microscopy for individual aerosol particle composition and morphology. The results show that the dominant cations in aerosols were Na+, (mean: 631 ng m−3), accounting for 63.8 % of the total cation and NH4 + (mean: 164 ng m−3), accounting for 13.8 % of the total cation measured in this study. The main inorganic anions were Cl (576 ng m−3, 54.1 %) and SO4 2− (596 ng m−3, 38.0 %). The main organic anion was oxalate (18 ng m−3). Crustal enrichment factor calculations identified 62 % of the trace elements measured (Cu, Ni, V, Co, Al, Mn, Fe, Sc, and Cr) with crustal origin. Single particle analysis demonstrated that 40 % of the aerosol particles examined were Cl rich particles as sodium chloride from seawater and 34 % of the total particles were Si-rich particles, mainly in the form of aluminosilicates from dust material. Based on the combination of air-mass trajectories, cluster analysis and principal component analysis, the major sources of these PM2.5 particles include marine, Saharan dust and biomass burning from West Africa; however, volcanic emissions from the Soufriere Hills in Montserrat had significant impact on aerosol composition in this region at the time of sample collection.


Datum: 03.05.2016


Photochemical activation of chlorine by iron-oxide aerosol

Abstract

The photochemical activation of chlorine by dissolved iron in artificial sea-salt aerosol droplets and by highly dispersed iron oxide (Fe2O3) aerosol particles (mainly hematite, specific surface ~150 m2 g−1) exposed to gaseous HCl, was investigated in humidified air in a Teflon simulation chamber. Employing the radical-clock technique, we quantified the production of gaseous atomic chlorine (Cl) from the irradiated aerosol. When the salt aerosol contained Fe2O3 at pH 6, no significant Cl production was observed, even if the dissolution of iron was forced by “weathering” (repeatedly freezing and thawing for five times). Adjusting the pH in the stock suspension to 2.6, 2.2, and 1.9 and equilibrating for one week resulted in a quantifiable amount of dissolved iron (0.03, 0.2, and 0.6 mmol L−1, respectively) and in gaseous Cl production rates of ~1.6, 6, and 8 × 1021 atoms cm−2 h−1, respectively. In a further series of experiments, the pure Fe2O3 aerosol was exposed to various levels of gaseous hydrogen chloride (HCl). The resulting Cl production rates ranged from 8 × 1020 Cl atoms cm−2 h−1 (at ~4 ppb HCl) to 5 × 1022 Cl atoms cm−2 h−1 (at ~350 ppb HCl) and confirmed the uptake and conversion of HCl to atomic Cl (at HCl to Cl conversion yields of 2–5 %, depending on the relative humidity). The Fe2O3 experiments indicate that iron-induced Cl formation may be important for highly soluble combustion-aerosol particles in marine environments in the presence of gaseous HCl.


Datum: 14.04.2016


Seasonal variation of bromocarbons at Hateruma Island, Japan: implications for global sources

Abstract

High-frequency measurements of dibromomethane (CH2Br2) and bromoform (CHBr3) at Hateruma Island, in the subtropical East China Sea, were performed using automated preconcentration gas chromatography/mass spectrometry. Their baseline concentrations, found in air masses from the Pacific Ocean, were 0.65 and 0.26 ppt, respectively, in summer and 1.08 and 0.87 ppt, respectively, in winter. Air masses transported from Southeast Asia were rich in bromocarbons, suggesting strong emissions in this area. The passage of cold fronts from the Asian continent was associated with sharp increases in observed concentrations of bromocarbons derived from coastal regions of the continent. Comparison of the relationships between [CH2Br2]/[CHBr3] and [CHBr3] in the Hateruma Island data with those in monthly mean data from 14 globally distributed U.S. National Oceanic and Atmospheric Administration ground stations suggested that these gases are produced primarily from a common process on a global scale.


Datum: 13.04.2016


Ambient volatile organic compounds in the atmosphere of industrial central India

Abstract

Volatile organic compounds (VOCs) are an important group of compounds because of their role in atmospheric chemistry and the risk they pose to human health and ecosystem. Therefore, the interest in determining VOCs in the atmosphere has increased over the last few decades to understand their emission, distribution, and sources. Considering the expanding urbanization and increasing use of fuels, very limited data of VOCs in India is available. This paper describes the chemical analysis of 12 light VOCs in 144 ambient air samples collected from three different sites near Raipur, India during a period of April, 2006-March, 2007 in order to understand their temporal and spatial distributions. This data has provided some important insights into the VOC profile, for the first time, of an industrial area in India. The annual average concentrations of all 12 VOCs in our study ranged from 43.2 to 160.4 μg m−3 (mean: 95.6 ± 31.0). The annual average concentration of individual VOCs in Raipur region ranged from 3.4 μg m−3 for xylenes to 18.3 μg m−3 for n-butane. n-Butane, i-butane, and propane were the three most abundant pollutants among all of the VOCs measured. The observed concentrations of these compounds in Raipur region were comparable to other Asian cities with some exceptions. The levels of total VOCs showed seasonal variations with a statistically significant winter maximum and lower values during summer and monsoon ranging from 55.9 ± 9.9 μg/m3 in August to 144.5 ± 15.5 μg/m3 in January. Sources of these VOCs have been described using species ratios and correlation studies.


Datum: 05.04.2016


A method for the selective measurement of HO 2 and RO 2 radical concentrations using a Nafion-PERCA system

Abstract

An instrument is developed for the measurement of peroxy radical using chemical amplification coupled with NO2-luminol chemiluminescence detection. The chain length of 147 ± 10 (1σ) is determined by an HO2 source that uses the photolysis of water vapor under 184.9 nm in air. A Nafion system equipped with a Nafion tube of ~2.2 mm external diameter and 350 mm length is employed in the PERCA instrument (Nafion-PERCA system). When flowing an air sample containing HO2 through the Nafion system, it is found that - 94.6 % of HO2 is removed. In contrast, only 17.8 % of RO2 radicals (a mixtures of CH3O2 and CH3C(O)O2 with a ratio of 1.1:0.9) are removed. The results indicate the Nafion system has a good selective removing performance of HO2 radical during the PERCA measurement. Therefore, the method could be applied to ambient and laboratory measurements of absolute concentrations of RO2 as well as the sum of HO2 and RO2.


Datum: 01.04.2016






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