Atmospheric Chemistry of Toxic Contaminants. 3. Unsaturated Aliphatics: Acrolein,Acrylonitrile, Maleic Anhydride

Detailed mechanisms are outlined for the chemical reactions that contribute to In-situ formation and atmospheric removal of the unsaturated aliphatic contaminants acrolein, acrylonitrile, and maleic anhydride. In-situ formation of small amounts of acrolein and maleic anhydride may Involve the reaction of OH (and O₃) with 1,3-dienes and the reaction of OH with aromatic hydrocarbons, respectively. There is no known pathway for In-situ formation of acrylonitrile. Rapid removal of acrolein (half-life = less than one day) and of maleic anhydride (half-life = several hours) is expected from their rapid reactions with OH (major), O₃, and NO₃. These reactions lead to formaldehyde and glyoxal from acrolein and to dicarbonyls from maleic anhydride. Acrylonitrile is removed at a slower rate (half-life = 2–7 days) by reaction with OH, leading to formaldehyde and formyl cyanide.     

Atmospheric Chemistry of Toxic Contaminants. 5. Unsaturated Halogenated Aliphatics: Allyl Chloride,Chloroprene, Hexachlorocyclopentadiene,Vinylidene Chloride

Detailed mechanisms are outlined for the chemical reactions involved In the atmospheric removal of four unsaturated chlorinated aliphatic contaminants, allyl chloride, chloroprene, hexachlorocyclopentadiene and vlnylldene chloride. Rate constants estimated from structure-reactivity relationships Indicate rapid removal for all four compounds by reactions with OH (major), ozone, and NO₃, with half-lives of 2-16 hrs for removal by reaction with OH. Reaction products of allyl chloride (formaldehyde, chloroacetaldehyde, peroxychloroacetyl nitrate) and vinylidene chloride (formaldehyde, phosgene, chloroacetyl chloride) are consistent with OH addition-Initiated pathways that include Cl atom elimination. The chlorine atoms produced In the OH reaction sequence react rapidly with all four unsaturated compounds, but these reactions are of negligible Importance for atmospheric removal of the four toxic contaminants studied. Analogous mechanisms are discussed for chloroprene (leading to formaldehyde, CH₂ = CCICHO, and CICOCHO) and for hexachlorocyclopentadlene (leading to oxalyl chloride and CICOCCI₂COCI).     

Atmospheric alcohols and aldehydes concentrations measured in Osaka,Japan and in Sao Paulo,Brazil

The use of alcohol fuel has received much attention since 1980s. In Brazil, ethanol-fueled vehicles have been currently used on a large scale. This paper reports the atmospheric methanol, ethanol and isopropanol concentrations which were measured from May to December 1997, in Osaka, Japan, where alcohol fuel was not used, and from 3 to 9 February 1998, in Sao Paulo, Brazil, where ethanol fuel was used. The alcohols were determined by the alkyl nitrite formation reaction using gas chromatography (GC-ECD) analysis. The concentration of atmospheric alcohols, especially ethanol, measured in Sao Paulo were significantly higher than those in Osaka. In Osaka, the average concentrations of atmospheric methanol, ethanol, and isopropanol were 5.8±3.8, 8.2±4.6, and 7.2±5.9 ppbv, respectively. The average ambient levels of methanol, ethanol, and isopropanol measured in Sao Paulo were 34.1±9.2, 176.3.±38.1, and 44.2±13.7 ppbv, respectively. The ambient levels of aldehydes, which were expected to be high due to the use of alcohol fuel, were also measured at these sampling sites. The atmospheric formaldehyde average concentration measured in Osaka was 1.9±0.9 ppbv, and the average acetaldehyde concentration was 1.5±0.8 ppbv. The atmospheric formaldehyde and acetaldehyde average concentrations measured in Sao Paulo were 5.0±2.8 and 5.4±2.8 ppbv, respectively. The C₂H₅OH/CH₃OH and CH₃CHO/HCHO were compared between the two measurement sites and elsewhere in the world, which have already been reported in the literature. Due to the use of ethanol-fueled vehicles, these ratios, especially C₂H₅OH/CH₃OH, are much higher in Brazil than these measured elsewhere in the world.     

Formation and Removal Reactions of Hazardous Air Pollutants

Current regulatory policies for hazardous air pollutants (HAPs) target the sources of direct emissions. In addition to direct emissions, some of the aromatic, nitrogenated, and oxygenated HAPs can be formed in the atmosphere. Formaldehyde and acetaldehyde, in particular, are produced by almost every hydrocarbon photooxidation reaction. Estimates have been made that, in some urban areas, in situ formation contributes as much as 85 percent of the ambient levels of formaldehyde and 95 percent for acetaldehyde. Over 40 percent of the HAPs being regulated under Title III of the 1990 Clean Air Act Amendments have atmospheric lifetimes of less than one day. The transformation products of these HAPs with low atmospheric persistence are important for assessing risks to human health, especially for cases where the transformation products are more toxic than the HAP itself.     

Products and mechanisms of the gas-phase reactions of OH radicals and O3 with 2-methyl-3-buten-2-ol

Products of the gas-phase reactions of OH radicals (in the presence of NO) and O₃ with the biogenic organic compound 2-methyl-3-buten-2-ol have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatography–mass spectrometry (GC-MS), gas chromatography with Fourier transform infrared detection (GC-FTIR), in situ FT-IR spectroscopy and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS/MS). Formaldehyde, 2-hydroxy-2-methylpropanal and acetone were identified from both the OH radical and O₃ reactions, glycolaldehyde and organic nitrate (s) were also observed from the OH radical reaction, and the OH radical formation yield from the O₃ reaction was measured. The formaldehyde, 2-hydroxy-2-methylpropanal, glycolaldehyde, acetone and organic nitrate yields from the OH radical reaction were 0.29±0.03, 0.19±0.07, 0.61±0.09, 0.58±0.04 and 0.05±0.02, respectively, and the formaldehyde, 2-hydroxy-2-methylpropanal and OH radical formation yields from the O₃ reaction were 0.29±0.03, 0.30±0.06 (0.47 from FT-IR measurements) and 0.19 (uncertain to a factor of 1.5), respectively. Acetone was also observed from the O₃ reaction, but appeared to be formed from secondary reactions. Reaction mechanisms are presented and discussed.     

Atmospheric Chemistry of Toxic Contaminants. 6. Nitrosamines: Dialkyl Nitrosamines and Nitrosomorpholine

Detailed mechanisms are outlined for the reactions that contribute to in-sltu formation and atmospheric removal of dlmethylnitrosamine, diethylnitrosamlne, methyl-ethylnltrosamine, and nitrosomorphollne. In-sltu formation involves the rapid reaction of amines with the hydroxyl radical, leading to nltrosamlnes, nltramlnes, amides, and aldehydes. Nitrosamlne photolysis accounts for their rapid daytime removal, leading to amlno radicals whose atmospheric reactions are also discussed.     

Carbonyl compounds in the urban environment of Athens,Greece

The concentration levels of 15 selected carbonyl compounds in 62 samples were determined at two sites in Athens basin from June to December 2000. Formaldehyde was the most abundant species (0.05-39 microg m(-3)), which comprised from 22% to 37% of the total measured compounds, followed by acetaldehyde (4.32-49 microg m(-3)), acetone/acrolein (0.64-198 microg m(-3)) and butanal (0.79-140 microg m(-3)). The mean formaldehyde/acetaldehyde and acetaldehyde/propanal molar ratios were calculated. No significant seasonal differences were observed for all the carbonyls. Photochemical production was found to weigh upon atmospheric levels for 83-93% in summer days, dropping below 33% in the winter. The importance of formaldehyde and acetaldehyde as a source of hydroxyl radicals in Athens was also assessed.     

Photochemical Pollution at Two Southern California Smog Receptor Sites

A one-year survey of air quality has been carried out at two southern California inland locations, Perris and Palm Springs (90 km E-SE and 120 km E of Los Angeles) to evaluate transport of photochemical smog from the Los Angeles area and to assess population exposure to toxic air pollutants in the Coachella Valley and eastern Riverside County. Air pollutants measured included formaldehyde, acetaldehyde, nitric acid, and peroxyacetyl nitrate (PAN). Acetic acid was also measured as part of the time-integrated method employed to measure PAN. In addition, intensive studies were carried out at both locations and included measurements of aldehydes, nitric acid, PAN, peroxypropionyl nitrate (PPN), methylchloroform and tetrachloroethylene.

Maximum concentrations of HCHO, CH₃CHO, HNO₃, PAN, PPN, CH₃COOH and C₂CI₄ were 26, 21, 4.5, 7.6, 0.42, 6.6 and 0.29 ppb in Palm Springs and 15, 30, 6.3, 9.1, 0.73, 7.8 and 0.43 ppb in Perris. Pollutant concentrations measured in Palm Springs and Perris are compared to those measured in the Los Angeles area, and are discussed in terms of formation and removal during transport.     

Atmospheric oxidation mechanisms of polychlorinated dibenzo-p-dioxins are different from those of benzene and dibenzofuran: a theoretical prediction

The reaction mechanisms of dibenzo-p-dioxin (DD) and 2,3,7,8-TCDD with OH radical have been studied using density functional theory calculations. Under the atmospheric conditions, ca 42% of DD + OH reaction proceeds as formation of DD − OH-β adduct, which will react with O₂ slowly; while the rest will proceed as formation of DD − OH-γ adduct, which will decompose to the substituted phenoxy radical P1 by the fused-ring C-O bond cleavage. For 2,3,7,8-TCDD + OH, the reaction will predominantly form the substituted phenoxy radical P2. The reaction mechanisms are drastically different from the peroxy mechanism for the atmospheric oxidations of benzene and dibenzofuran.     

Volatile carbonylic compounds in downtown Santiago, Chile

Formaldehyde, acetaldehyde, acetone, propanal, butanal, 2-butenal, 3-methylbutanal, hexanal, benzaldehyde, 2-methylbenzaldehyde, and 2,5-dimethylbenzaldehyde were measured during six spring days at downtown Santiago de Chile. Measurements were performed 24h/day and averaged over three hour periods. The averages of the maxima (ppbv) were, formaldehyde: 3.9+/-1.4; butanal: 3.3+/-3.4; acetaldehyde: 3.0+/-0.9; acetone: 2.4+/-1.0; 2-butenal: 0.56+/-0.52; propanal: 0.46+/-0.21; benzaldehyde: 0.34+/-0.3; 3-butanal: 0.11+/-0.05; hexanal: 0.11+/-0.08; 2-methylbenzaldehyde: 0.08+/-0.05; 2,5-dimethylbenzaldehyde: 0.05+/-0.03. Aliphatic aldehydes (C1-C3) are strongly correlated among them and weakly with primary (toluene) and secondary (ozone plus nitrogen dioxide or PAN) pollutants. In particular, the correlation between acetaldehyde and propanal values remains even if diurnal and nocturnal data are considered separately, indicating similar sources. All these aldehydes present maxima values in the morning (9-12h) and minima at night (0-3h). The best correlation is observed when butanal and 2-butenal data are considered (r=0.99, butanal/2-butenal=6.2). These compounds present maxima values during the 3-6h period, with minima values in the 0-3h period. These data imply a strong pre-dawn emission. Other aldehydes show different daily profiles, suggesting unrelated origins. Formaldehyde is the aldehyde whose concentration values best correlate with the levels of oxidants. The contribution of primary emissions and photochemical processes to formaldehyde concentrations were estimated by using a multiple regression. This treatment indicates that (32+/-16)% of measured values arise from direct emissions, while (79+/-23)% is attributable to secondary formation.     

Carbonyls in the metropolitan area of Mexico City: calculation of the total photolytic rate constants Kp(s(-1)) and photolytic lifetime (tau) of ambient formaldehyde and acetaldehyde

A great number of studies on the ambient levels of formaldehyde and other carbonyls in the urban rural and maritime atmospheres have been published because of their chemical and toxicological characteristics, and adverse health effects. Due to their toxicological effects, it was considered necessary to measure these compounds at different sites in the metropolitan area of Mexico City, and to calculate the total rate of photolytic constants and the photolytic lifetime of formaldehyde and acetaldehyde. Four sites were chosen. Sampling was carried out at different seasons and atmospheric conditions. The results indicated that formaldehyde was the most abundant carbonyl, followed by acetone and acetaldehyde. Data sets obtained from the 4 sites were chosen to calculate the total rate of photolysis and the photolytic lifetime for formaldehyde and acetaldehyde. Maximum photolytic rate values were obtained at the maximum actinic fluxes, as was to be expected.     

Sources and photodecomposition of formaldehyde and acetaldehyde in Rome ambient air

Atmospheric levels of formaldehyde and acetaldehyde as well as their diurnal and seasonal variations were investigated from 1994 to 1997 in downtown Rome during sunny and wind calm days. Hourly concentrations of formaldehyde ranged from 8 to 28 ppbV in summer and 7 to 17 ppbv in winter; acetaldehyde concentrations varied correspondingly within the 3–18 and 2–7 ppbv intervals. Percentages of both aldehydes photochemically produced were estimated through a simple relationship based upon the comparison of individual ratios of formaldehyde and acetaldehyde to toluene in ambient air and automobile emission. Photochemical production was found to weigh upon atmospheric levels for 80–90% in summer days. It dropped below 35% in the winter period, when direct emission from traffic largely predominated. Photochemical summer source was more efficient for acetaldehyde than for formaldehyde, especially in the early morning. The importance of formaldehyde as the major source of hydroxyl radicals in Rome was also assessed.     

Residential indoor,outdoor, and workplace concentrations of carbonyl compounds: relationships with personal exposure concentrations and correlation with sources

Personal 48-hr exposures of 15 randomly selected participants as well as microenvironment concentrations in each participant's residence and workplace were measured for 16 carbonyl compounds during summer-fall 1997 as a part of the Air Pollution Exposure Distributions within Adult Urban Populations in Europe (EXPOLIS) study in Helsinki, Finland. When formaldehyde and acetaldehyde were excluded, geometric mean ambient air concentrations outside each participant's residence were less than 1 ppb for all target compounds. Geometric mean residential indoor concentrations of carbonyls were systematically higher than geometric mean personal exposures and indoor workplace concentrations. Additionally, residential indoor/outdoor ratios indicated substantial indoor sources for most target compounds. Carbonyls in residential indoor air correlated significantly, suggesting similar mechanisms of entry into indoor environments. Overall, this study demonstrated the important role of non-traffic-related emissions in the personal exposures of participants in Helsinki and that comprehensive apportionment of population risk to air toxics should include exposure concentrations derived from product emissions and chemical formation in indoor air.     

Oxidation of diethylene glycol with ozone and modified Fenton processes

This paper describes a study of oxidation of diethylene glycol (DEG) by ozone and modified Fenton process (hydrogen peroxide and ferric salt mixture) in aqueous solution. Both oxidation processes were able to oxidize relatively high concentrations of DEG effectively. DEG reacted primarily through hydroxyl radical produced by decomposition of ozone, and about 3 mol of ozone were consumed per mole of DEG removed during the process. For modified Fenton oxidation, stepwise addition of hydrogen peroxide (H2O2) and ferric salt (Fe(III)) resulted in much higher removal of DEG than one-time pulse addition of the chemicals. The extent of DEG removal increased with increasing concentrations of both H2O2 and Fe(III). Oxidant consumption per mole of DEG oxidized was one order of magnitude higher for hydrogen peroxide than those observed for ozone. Overall, ozonation produced higher concentrations of aldehydes, and modified Fenton treatment produced higher concentrations of carboxylic acids for the same levels of DEG oxidation. The major products of ozonation were glycolaldehyde, glyoxal, formaldehyde, acetaldehyde, and acetic, formic, pyruvic, oxalic and glyoxalic acids. The major products of modified Fenton oxidation were formaldehyde, and formic and acetic acids.     

A modelling assessment of the atmospheric fate of volatile methyl siloxanes and their reaction products

Volatile methyl siloxanes break down in the atmosphere by reacting with OH radicals to form OH-substituted silanols. As the silanols become increasingly OH substituted they are increasingly likely to be removed from the atmosphere by wet and dry deposition. A simple equilibrium partitioning model was constructed to explore the relative rates of removal by different mechanisms (reaction vs. deposition) for siloxanes and their resultant silanols. A mass balance is calculated for the parent siloxane molecule and for each silanol, characterised by the number of OH substitutions. The model includes the effect of incomplete equilibrium between the vapour, adsorbed and dissolved phases of silanols in the atmosphere using a non-equilibrium factor (epsilon) expressing relative departure from equilibrium. Model results show: (1) maximum vapour-phase concentrations for non-substituted siloxanes and single-OH-substituted silanols; (2) maximum dissolved-phase and adsorbed-phase concentrations for two-OH-substituted silanols; (3) >99% of the original material will be removed in wet deposition and <1% in dry deposition as silanols. For increasing OH-substitutions, the decreasing concentration of precursor molecules (as a consequence of combined removal processes) means that concentrations are negligible, in all phases, beyond three or four substitutions. Predictions were relatively insensitive to assumed departures from phase equilibrium. Predictions of silanol hydrolysis in liquid water droplets suggest that the mix of diol chain lengths in precipitation may not be in thermodynamic equilibrium and will depend on atmospheric residence time and pH.     

Carbon isotope analysis for source identification of atmospheric formaldehyde and acetaldehyde in Dinghushan Biosphere Reserve in South China

Formaldehyde and acetaldehyde are two most abundant carbonyls in ambient air. Biogenic emission has been proposed as a significant source other than anthropogenic emissions and atmospheric secondary formation. Here at a forest site in South China, the carbon isotopic compositions of formaldehyde and acetaldehyde emitted from leaves of three tree species (Litsea rotundifolia, Canarium album and Castanea henryi) were measured in comparison with the bulk carbon isotopic compositions of tree leaves. δ¹³C data of the emitted aldehydes (from ?31‰ to ?46‰) were quite different for tree species, which were all more depleted in ¹³C than the tree-leaf bulk δ¹³C values (from ?27‰ to ?32‰). Formaldehyde in ambient air at the forest site had δ¹³C values different from those of leaf-emitted formaldehyde, indicating other sources for ambient formaldehyde apart from direct emission from leaves, most probably the photooxidation of biogenic hydrocarbon like isoprene and monoterpene. The δ¹³C differences of acetaldehyde between ambient data and those of tree leaves emission were less than 1‰, implying direct biogenic emission as the dominant source.     

Residential Indoor,Outdoor, and Workplace Concentrations of Carbonyl Compounds: Relationships with Personal Exposure Concentrations and Correlation with Sources

Abstract

Personal 48-hr exposures of 15 randomly selected participants as well as microenvironment concentrations in each participant’s residence and workplace were measured for 16 carbonyl compounds during summer–fall 1997 as a part of the Air Pollution Exposure Distributions within Adult Urban Populations in Europe (EXPOLIS) study in Helsinki, Finland. When formaldehyde and acetaldehyde were excluded, geometric mean ambient air concentrations outside each participant’s residence were less than 1 ppb for all target compounds. Geometric mean residential indoor concentrations of carbonyls were systematically higher than geometric mean personal exposures and indoor workplace concentrations. Additionally, residential indoor/outdoor ratios indicated substantial indoor sources for most target compounds. Carbonyls in residential indoor air correlated significantly, suggesting similar mechanisms of entry into indoor environments. Overall, this study demonstrated the important role of non-traffic-related emissions in the personal exposures of participants in Helsinki and that comprehensive apportionment of population risk to air toxics should include exposure concentrations derived from product emissions and chemical formation in indoor air.     

Chemistry of Atmospheric Oxidants

All of the important oxidants in polluted air are formed there by chemical reactions which occur among the primary pollutants. The most abundant of these oxidants is ozone which is formed in a cycle involving nitric oxide, nitrogen dioxide, atmospheric oxygen, and hydrocarbons. This ozone is best understood, not as a reaction product, but as an intermediate in steady-state concentration between formation and disappearance reactions. Hydrocarbons permit accumulation of ozone by reacting to scavenge the nitric oxide which would otherwise remove the ozone. The amount of ozone which can be formed in ambient polluted air is limited to about 1 ppm because these scavenging reactions become less effective when the nitric oxide concentration becomes very small. The peroxyacyl nitrates are a group of oxidants which result from reactions between oxides of nitrogen and organic pollutants. Olefinic and aromatic hydrocarbons make the largest contribution to PAN formation; saturates contribute little if any. The role of nitrogen dioxide and other oxidizing agents is also discussed.     

Characterisation of urban inhalation exposures to benzene,formaldehyde and acetaldehyde in the European Union

BACKGROUND, AIM AND SCOPE: All across Europe, people live and work in indoor environments. On average, people spend around 90% of their time indoors (homes, workplaces, cars and public transport means, etc.) and are exposed to a complex mixture of pollutants at concentration levels that are often several times higher than outdoors. These pollutants are emitted by different sources indoors and outdoors and include volatile organic compounds (VOCs), carbonyls (aldehydes and ketones) and other chemical substances often adsorbed on particles. Moreover, legal obligations opposed by legislations, such as the European Union's General Product Safety Directive (GPSD) and Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), increasingly require detailed understanding of where and how chemical substances are used throughout their life-cycle and require better characterisation of their emissions and exposure. This information is essential to be able to control emissions from sources aiming at a reduction of adverse health effects. Scientifically sound human risk assessment procedures based on qualitative and quantitative human exposure information allows a better characterisation of population exposures to chemical substances. In this context, the current paper compares inhalation exposures to three health-based EU priority substances, i.e. benzene, formaldehyde and acetaldehyde. MATERIALS AND METHODS: Distributions of urban population inhalation exposures, indoor and outdoor concentrations were created on the basis of measured AIRMEX data in 12 European cities and compared to results from existing European population exposure studies published within the scientific literature. By pooling all EU city personal exposure, indoor and outdoor concentration means, representative EU city cumulative frequency distributions were created. Population exposures were modelled with a microenvironment model using the time spent and concentrations in four microenvironments, i.e. indoors at home and at work, outdoors at work and in transit, as input parameters. Pooled EU city inhalation exposures were compared to modelled population exposures. The contributions of these microenvironments to the total daily inhalation exposure of formaldehyde, benzene and acetaldehyde were estimated. Inhalation exposures were compared to the EU annual ambient benzene air quality guideline (5 microg/m3-to be met by 2010) and the recommended (based on the INDEX project) 30-min average formaldehyde limit value (30 microg/m3). RESULTS: Indoor inhalation exposure contributions are much higher compared to the outdoor or in-transit microenvironment contributions, accounting for almost 99% in the case of formaldehyde. The highest in-transit exposure contribution was found for benzene; 29.4% of the total inhalation exposure contribution. Comparing the pooled AIRMEX EU city inhalation exposures with the modelled exposures, benzene, formaldehyde and acetaldehyde exposures are 5.1, 17.3 and 11.8 microg/m3 vs. 5.1, 20.1 and 10.2 microg/m3, respectively. Together with the fact that a dominating fraction of time is spent indoors (>90%), the total inhalation exposure is mostly driven by the time spent indoors. DISCUSSION: The approach used in this paper faced three challenges concerning exposure and time-activity data, comparability and scarce or missing in-transit data inducing careful interpretation of the results. The results obtained by AIRMEX underline that many European urban populations are still exposed to elevated levels of benzene and formaldehyde in the inhaled air. It is still likely that the annual ambient benzene air quality guideline of 5 microg/m3 in the EU and recommended formaldehyde 30-min average limit value of 30 microg/m3 are exceeded by a substantial part of populations living in urban areas. Considering multimedia and multi-pathway exposure to acetaldehyde, the biggest exposure contribution was found to be related to dietary behaviour rather than to inhalation. CONCLUSIONS: In the present study, inhalation exposures of urban populations were assessed on the basis of novel and existing exposure data. The indoor residential microenvironment contributed most to the total daily urban population inhalation exposure. The results presented in this paper suggest that a significant part of the populations living in European cities exceed the annual ambient benzene air quality guideline of 5 microg/m3 in the EU and recommended (INDEX project) formaldehyde 30-min average limit value of 30 microg/m3. RECOMMENDATIONS AND PERSPECTIVES: To reduce exposures and consequent health effects, adequate measures must be taken to diminish emissions from sources such as materials and products that especially emit benzene and formaldehyde in indoor air. In parallel, measures can be taken aiming at reducing the outdoor pollution contribution indoors. Besides emission reduction, mechanisms to effectively monitor and manage the indoor air quality should be established. These mechanisms could be developed by setting up appropriate EU indoor air guidelines.