Size-segregated chemistry of particulate dicarboxylic acids in the Arctic atmosphere

Gas–particle interactions of low-molecular-weight dicarboxylic acids were studied at a coastal Arctic site during the summer. Size segregated measurements with a Berner low-pressure impactor displayed up to four modes for ionic compounds: an Aitken mode, an accumulation mode, and two supermicron modes. The lower supermicron mode was ascribed to sea-salt, whereas the upper mode consisted mostly of species associated with continental particles. All four modes could be identified for oxalic acid, with the lower supermicron mode being the dominant. Malonic acid displayed a supermicron mode but was not found in the submicron size range. Succinic acid had an accumulation mode and, in a few samples, a supermicron mode. Glutaric acid displayed sometimes and accumulation mode, sometimes a supermicron mode, and occasionally both. The most probable formation pathway for submicron oxalic and glutaric acid was condensation from the gas phase, even though production in cloud droplets cannot be ruled out either. A slightly different formation pathway may have been important for submicron succinic acid production. Supermicron oxalic acid was probably formed by condensation from the gas-phase, by heterogeneous reactions occurring on the surface of pre-existing sea-salt and continental particles, or in cloud droplets. A larger mass median diameter for supermicron malonic and glutaric acid might be indicative of liquid-phase production in aqueous sea-salt particles. Evidence on possibly substantial sampling artifacts related to measuring dicarboxylic acids using filters were also obtained.     

Ammonia in the atmosphere: a review on emission sources, atmospheric chemistry and deposition on terrestrial bodies

Gaseous ammonia (NH₃) is the most abundant alkaline gas in the atmosphere. In addition, it is a major component of total reactive nitrogen. The largest source of NH₃ emissions is agriculture, including animal husbandry and NH₃-based fertilizer applications. Other sources of NH₃ include industrial processes, vehicular emissions and volatilization from soils and oceans. Recent studies have indicated that NH₃ emissions have been increasing over the last few decades on a global scale. This is a concern because NH₃ plays a significant role in the formation of atmospheric particulate matter, visibility degradation and atmospheric deposition of nitrogen to sensitive ecosystems. Thus, the increase in NH₃ emissions negatively influences environmental and public health as well as climate change. For these reasons, it is important to have a clear understanding of the sources, deposition and atmospheric behaviour of NH₃. Over the last two decades, a number of research papers have addressed pertinent issues related to NH₃ emissions into the atmosphere at global, regional and local scales. This review article integrates the knowledge available on atmospheric NH₃ from the literature in a systematic manner, describes the environmental implications of unabated NH₃ emissions and provides a scientific basis for developing effective control strategies for NH₃.     

Ubiquity of bisphenol A in the atmosphere

Bisphenol A (BPA) is a suspected endocrine disruptor in the environment. However, little is known about its distribution and transport in the atmosphere. Here, the concentrations of BPA in the atmospheric aerosols from urban, rural, marine, and the polar regions were measured using solvent extraction/derivatization and gas chromatography/mass spectrometry technique. The concentrations of BPA (1-17,400 pg m⁻³) ranged over 4 orders of magnitude in the world with a declining trend from the continent (except for the Antarctica) to remote sites. A positive correlation was found between BPA and 1,3,5-triphenylbenzene, a tracer for plastic burning, in urban regions, indicating that the open burning of plastics in domestic waste should be a significant emission source of atmospheric BPA. Our results suggest that the ubiquity of BPA in the atmosphere may raise a requirement for the evaluation of health effects of BPA in order to control its emission sources, for example, from plastic burning.     

Transfer of visible radiation in the atmosphere

The problem of the transfer of visible radiation in the terrestrial atmosphere is addressed from the visual-air-quality point-of-view. Attention is therefore focused on computations of the luminance, dominant wavelength, and spectral purity of the sky radiation requiring radiance values for a number of wavelengths in the 0.38–0.78 μm interval of the electromagnetic spectrum. These colorimetric parameters are determined, for five different plane-parallel atmospheric models, from values of the radiances at 23 unequally spaced wavelengths. The diffuse radiation is evaluated after taking into account all orders of scattering, but after neglecting the polarization aspects of the scattered radiation. The atmospheric models studied are for average, cloudfree, mid-latitude summer conditions, and vary from an aerosol-free, absorption-free model at one end to a model with a very large amount of aerosols and absorption by ozone, water vapor and oxygen at the other. These models are assumed to rest on a ground obeying Lambert's law of reflection.Discussion of results is confined to variations of the aforementioned colorimetric parameters as a function of the zenith angle of observation in a vertical plane passing through the sun and the observer, but for several positions of the sun, and for several atmospheric conditions. For a few selected cases, results obtained after including all orders of scattering are compared with those obtained after consideration of the first scattering of the incoming solar, and outgoing ground-reflected radiation.The main features of the sunlit sky for various cloud free atmospheric conditions and for various sun's positions are, qualitatively speaking, well-reproduced by the model calculations. Attention is drawn to the need for a detailed comparison of the colorimetric measurements taken simultaneously with the observations of various atmospheric parameters of crucial importance, and computations carried out with the input parameters representative of the experimental conditions; and also to the need for including absorption by other gases and sphericity of the earth-atmosphere system in future modeling studies.     

Alkyl sulfonic acids in the atmosphere

A gas Chromatographie technique, based on methylation with diazomethane and specific sulfur detection (FDP), is proposed for the on-filter speciation of add aerosol constituents. First results indicate, that apart from sulfuric acid (and/or acid sulfate) the atmospheric aerosol may contain sulfurous acid (and/or acid sulfite) and sulfonic acid. The latter are postulated to be products from the atmospheric oxidation of sulfides, disulfides and mercaptans.     

Chiral organochlorine pesticides in the atmosphere

We measured the enantiomeric fractions (EF) of various organochlorine pesticides in air samples from Indiana, Arkansas, and Louisiana collected in 2002–2003. Enantiomeric fractions for o,p′-DDD are reported here for the first time, and they suggest preferential depletion of one enantiomer over the other, with a mean value of 0.44. For the chlordanes, the EFs followed the same trends as reported in previous studies. EF values for trans-chlordane (TC) were slightly below 0.5, and values for cis-chlordane (CC) were slightly above 0.5. For cis-heptachlor epoxide (HEPX), the EF values averaged 0.65, indicating a clear preferential depletion of the (−)-enantiomer. For TC and CC, no clear distinction could be made between the values measured among the three sites, suggesting that it is not possible to use these EF values as “source signatures”. For HEPX, the Indiana site had significantly higher EF values than did the Arkansas site; this difference may reflect differences in the historic use of heptachlor in these two regions.     

Sampling of carbonaceous particles in the atmosphere

A method for measurement of atmospheric carbonaceous particulate matter is proposed and evaluated. A diffusion denuder, placed ahead of a filter, is used to exclude vapor-phase organic compounds which might be retained by adsorption on the filter. The carbonaceous material lost by volatilization from the filter after collection is retained with a fluidized bed of powdered Al₂O₃. The efficiencies of the denuder and Al₂O₃ were evaluated with vapor phase phenanthrene and octadecane. Atmospheric sampling was done at two urban and one background site in California using the proposed technique in parallel with conventional hi-vol and dichotomous samplers. Hi-vol samples appear to have lost up to half of the particle phase carbon during sampling. About half this error could be eliminated by sampling at low face velocity. The effects of face velocity appear to distort the proportions of fine and coarse particulate carbon obtained with a dichotomous sampler.     

Volatile organic compounds in the atmosphere of forests

The procedure of sampling and gas chromatographic-mass spectrometric analysis of air containing volatile emissions from living plants has been elaborated. The qualitative composition of volatile organic compounds (VOC) produced by 22 species of plants which are characteristic for Northern hemisphere forests has been studied. The emission rate of isoprene and terpenes for some of them has been determined. Terpene concentrations in coniferous forests of different regions of the U.S.S.R. have been also determined. The list of compounds identified includes more than 70 substances of different classes. Total terpene concentrations in the coniferous forests air usually vary from 3.5 to 35 μg⁻³. Strong influence of meteorological conditions on the emission rate and terpene concentrations in the air under the forest canopy has been noted.     

Evolution of vehicle exhaust particles in the atmosphere

Aerosol mass spectrometer (AMS) measurements are used to characterize the evolution of exhaust particulate matter (PM) properties near and downwind of vehicle sources. The AMS provides time-resolved chemically speciated mass loadings and mass-weighted size distributions of nonrefractory PM smaller than 1 microm (NRPM1). Source measurements of aircraft PM show that black carbon particles inhibit nucleation by serving as condensation sinks for the volatile and semi-volatile exhaust gases. Real-world source measurements of ground vehicle PM are obtained by deploying an AMS aboard a mobile laboratory. Characteristic features of the exhaust PM chemical composition and size distribution are discussed. PM mass and number concentrations are used with above-background gas-phase carbon dioxide (CO2) concentrations to calculate on-road emission factors for individual vehicles. Highly variable ratios between particle number and mass concentrations are observed for individual vehicles. NRPM1 mass emission factors measured for on-road diesel vehicles are approximately 50% lower than those from dynamometer studies. Factor analysis of AMS data (FA-AMS) is applied for the first time to map variations in exhaust PM mass downwind of a highway. In this study, above-background vehicle PM concentrations are highest close to the highway and decrease by a factor of 2 by 200 m away from the highway. Comparison with the gas-phase CO2 concentrations indicates that these vehicle PM mass gradients are largely driven by dilution. Secondary aerosol species do not show a similar gradient in absolute mass concentrations; thus, their relative contribution to total ambient PM mass concentrations increases as a function of distance from the highway. FA-AMS of single particle and ensemble data at an urban receptor site shows that condensation of these secondary aerosol species onto vehicle exhaust particles results in spatial and temporal evolution of the size and composition of vehicle exhaust PM on urban and regional scales.     

Temperature dependence of PCBs in the UK atmosphere

A thermodynamic approach was taken to assess the state of equilibrium between air and the Earth’s surface for PCBs at a variety of sites located in urban and rural areas. The Clausius–Clapeyron equation was applied to atmospheric PCB data, relating PCB partial vapour pressure (ln P) to inverse temperature (1/K); essentially representing the temperature controlled transition between condensed phases and the atmospheric gas phase. The slopes of the resulting plots ranged from −3100 to −8272 for a range of congeners at two city sites, significantly steeper than those generated at two rural locations, where there was little or no correlation between ln P and temperature. It was inferred that advection and variable meteorological conditions mask any localised, temperature dependent, air–surface exchange at these rural locations when weekly or two weekly integrated samples were taken. At a third rural site, close to Lancaster University, an intensive highly time-resolved sampling regime, carried out during very stable meteorological conditions resulted in highly correlated plots (r²>0.6), with slopes ranging from −7151 to −14 148 for different congeners. By reducing meteorological variables in this manner localised temperature controlled air–surface exchange became evident. Enthalpies of phase change generated from the temperature coefficients were similar to literature values for the enthalpy of vapourisation and the enthalpy of phase change from octanol to air. This suggests that, under these stable conditions, equilibrium was achieved as a function of either vapour pressure (P^°_L) or the octanol–air partition coefficient (K_OA).     

Measurement of methyl halides in the marine atmosphere

An analytical method for measuring atmospheric methyl halides was established based on canister sampling and capillary GC/MS. Stability tests for air samples collected in two kinds of canisters (electro-chemical buffing and fused-silica lined) with smooth inner surfaces, showed that both provided stable storage for CH₃Cl, CH₃Br, and CH₃I. The method was applied to the measurement of methyl halides at a remote island (Okinawa, Japan) in August 1996, where nocturnal ozone depletion had been observed in summer. We found that atmospheric CH₃Cl increased during stable nights and was negatively correlated with surface ozone concentration. The highest CH₃Cl concentration amounted to as high as 1400 pptv and indicated that CH₃Cl emitted from the surrounding coastal areas had accumulated in the boundary layer under a stable atmosphere at that time. A positive correlation was observed between CH₃Br and CH₃I, suggesting a common source in the area.     

Homogeneous oxidation of sulphur compounds in the atmosphere

Work carried out under the European COST 61a Project on the homogeneous oxidation of sulphur compounds in the atmosphere is briefly reviewed. Mechanisms for sulphur dioxide can be divided into three classes;

• 1.(a) oxidation by free radicals generated photochemically,
• 2.(b) oxidation by intermediates produced in thermal reactions, and
• 3.(c) direct photo-oxidation.

Only (a) makes a substantial contribution to SO₂ oxidation with calculated maximum rates of between 2 and 6% h⁻¹ in sunlight irradiated urban air during summer months and 1–2% h⁻¹ in unpolluted air. Most of the oxidation is brought about by the attack of the OH radical on SO₂ but the contribution of RO₂ radical attack is not well determined due to uncertainties in RO₂ rate constants. H₂S, CH₃SH and (CH₃)₂S react with OH radicals giving atmospheric life-times about 1 day.     

Smoke concentration in the greater Cairo atmosphere

A study of smoke content of the atmosphere over the Greater Cairo area was conducted during the 12 months from June 1977 to May 1978. Smoke samples were taken continuously over two-hour periods at two sites, one in Shubra El-Kheima industrial sector on the northern boundary of the study area and the other in a purely residential district about 15 km south-south-west of the first site.A comparison was made between the averaged concentrations at both sites. It was found that the industrial area was considerably higher in smoke contamination and that industrial activity is the principal source of smoke in the Cairo atmosphere.Daily and yearly cycles of smoke concentration were also studied and discussed in terms of man-made source activities and meteorological conditions. Concentrations were found to be much higher in the cold months. The daily cycle rhythm was the same at the two sites, having two well developed maxima in the morning and late evening and a pronounced minimum in the mid-afternoon. Daily maxima were almost of the same order of magnitude in each site. The morning maximum seemed to be formed by fumigation just after sunrise in the industrial sector and appeared two hours later in the downwind residential district.No significant difference was found between smoke concentrations during weekdays and weekends.     

Efficiency of filter sampling for arsenic in the atmosphere

The efficiency of hi-vol samplers with glass fiber filters for collection of atmospheric arsenic was assessed by parallel sampling with a technique able to retain both particle and gas-phase arsenic trioxide. Sampling was done adjacent to the Kennecott copper smelter in Magna, Utah during the winter of 1981. Arsenic concentrations up to 0.2 μg m⁻³ (24-h average) were observed. The hi-vol sampler retained, on average, 83% of the As retained by the parallel sampler, implying at least 17% As penetration through the glass fiber filter. Laboratory evaluations of the sampling and analytical method are also presented.