Characteristics of atmospheric carbonyls and VOCs in Forest Park in South China

Origins of formaldehyde in a mountainous background atmosphere of southern China

Formaldehyde (HCHO) is one of the key indicators of severe photochemical pollution and strong atmospheric oxidation capacity in southern China. However, current information on the origins of regional HCHO and the impacts of polluted air masses remains scarce and unclear. In this study, an intensive observation of HCHO was conducted at a mountainous background site in southern China during typical photochemical pollution episodes. The concentrations of HCHO reached up to 6.14 ppbv and averaged at 2.68 ± 1.11 ppbv. Source appointment using a photochemical age-based parameterization method revealed significant contributions of secondary formation (50 %) and biomass burning (42 %). Meanwhile, under the influence of the East Asian Winter Monsoon, polluted air masses from central and western China can significantly increase the regional HCHO levels. The simulation results adopting the Rapid Adaptive Optimization Model for Atmospheric Chemistry model further demonstrated that the intrusion of active anthropogenic pollutants (e.g., small-molecule alkenes) can accelerate the net production rate of HCHO, particularly through BVOC-oxidation pathways. This study suggests a potential enhanced mechanism of HCHO production resulting from anthropogenic-biogenic interactions. It highlights that polluted air masses carrying abundant HCHO from upwind areas may facilitate severe photochemical pollution in the Greater Bay Area.

Comprehensive observations of carbonyls of Mt. Hua in Central China: Vertical distribution and effects on ozone formation

Oxygenated volatile organic compounds (OVOCs) play important roles in tropospheric chemistry, regulating the oxidation capacity and ozone (O3) formation potential of the atmosphere. However, the evolution of OVOCs composition during vertical transport from the near surface to the upper atmosphere layer and the roles of OVOCs in the alpine atmospheric O3 formation are still poorly understood. In this study, we investigated the carbonyl compounds, the most important chemical group of OVOCs, and other gaseous pollutants simultaneously collected at the top (2060 m a.s.l, Top) and the foot (402 m a.s.l, Foot) of Mt. Hua in August 2020. The average concentrations of the total quantified carbonyl compounds (∑carbonyls) at the Top and Foot were 16.05 ± 3.69 and 15.32 ± 5.63 ppbv, respectively. Acetone was the most abundant carbonyl (4.19 ± 1.01 ppbv) at the Top, followed by formaldehyde and n-Nonanal, accounting for ∼58.8 % of ∑carbonyls, while formaldehyde (5.40 ± 2.26 ppbv), acetone, and acetaldehyde were the three most abundant species at the Foot, accounting for 64.7 % of ∑carbonyls. The n-Nonanal, acetone and acetaldehyde showed positive correlations between the Top and Foot during daytime, confirming the vertical transport of carbonyls from the foot to the top of Mt. Hua under the influence of valley winds. The direct emissions from vegetation, transport processes of anthropogenic emissions and photochemical oxidation contributed significantly to the measured carbonyls at the Top, especially for acetone. Formaldehyde, acetaldehyde, glyoxal, and methylglyoxal were the most important contributors to the O3 generation in Mt. Hua. This study could advance our understanding of the vertical distribution of the carbonyls and the effects on O3 formation in the alpine region of China.

Explication on distribution patterns of volatile organic compounds in petro-chemistry and oil refineries of China using a species-transport model and health risk assessment

Volatile organic compounds (VOCs) from industrial emissions have attracted great attention due to their negative effects on human, but there is lack of deterministic air quality model for VOC emissions. In this study, airborne VOCs from a typical petrochemical and oil refinery region, Lanzhou, Gansu province of China, were on-site measured. The regional pollution patterns were investigated using a species transport model and the health risks were evaluated. The spatial distribution of VOCs showed that 87.5 % of the airborne VOCs were benzene, toluene, ethylbenzene, and xylene having higher concentration (146 μg/m³) in the north direction oil refinery industrial areas. The concentrations of toluene and benzene were as high as 41.5 and 33.3 μg/m³ in the 4 km² area away from the petrochemical emission source, respectively, and the concentration of o-/m + p-xylene was up to 79.7 μg/m³. Based on the measured concentration data, the numerical results showed that the accumulation of high concentration of VOC species by mass transfer in the region is related to the atmospheric diffusion driven by downward-moving air over the valley areas. Non-carcinogenic risk assessments showed that airborne benzene exposure had acceptable hazard quotient of 0.185 for adults, which was 1.8 times of children's (0.102), whereas it was found that a high carcinogenic risk (>10^-4) from benzene in several sampling sites and diffuse distance become significant for carcinogenic risk. This study verified the effectiveness of VOC atmospheric diffusion model through a large number of on-site monitoring data, providing data support for model-based risk assessment.

Atmospheric Carbonyl Compounds in the Central Taklimakan Desert in Summertime: Ambient Levels, Composition and Sources

Although carbonyl compounds are a key species with atmospheric oxidation capacity, their concentrations and sources have not been sufficiently characterized in various atmospheres, especially in desert areas. In this study, atmospheric carbonyl compounds were measured from 16 May to 15 June 2018 in Tazhong in the central Taklimakan Desert, Xinjiang Uygur Autonomous Region, China. Concentrations, chemical compositions, and sources of carbonyl compounds were investigated and compared with those of different environments worldwide. The average concentration of total carbonyls during the sampling period was 11.79 ± 4.03 ppbv. Formaldehyde, acetaldehyde, and acetone were the most abundant carbonyls, with average concentrations of 6.08 ± 2.37, 1.68 ± 0.78, and 2.52 ± 0.68 ppbv, respectively. Strong correlations between formaldehyde and other carbonyls were found, indicating same or similar sources and sinks. A hybrid single-particle Lagrangian integrated trajectory was used to analyze 72 h back trajectories. The values of C1/C2 (formaldehyde to acetaldehyde, 3.22–4.59) and C2/C3 (acetaldehyde to propionaldehyde, 15.00–17.03) from different directions and distances of the trajectories were consistent with the characteristics of a remote area. Relative to various environments, the carbonyl concentration in the Tazhong desert site was lower than that in urban areas and higher than that in suburban and remote areas, implying contributions from local primary and secondary sources. The obtained data can be used to improve the source and sink estimation of carbonyls at the regional scale.

Spatial and temporal distribution characteristics and ozone formation potentials of volatile organic compounds from three typical functional areas in China

BACKGROUND

Ozone is currently one of the most important air pollutants. Volatile organic compounds (VOCs) can easily react with atmospheric radicals to form ozone. In-field measurement of VOCs may help in estimating the local VOC photochemical pollution level.

METHOD

This study examined the spatial and temporal distribution characteristics of VOCs during winter at three typical sites of varying classification in China; industrial (Guangzhou Economic and Technological Development District (GETDD)), urban (Guangzhou higher education mega center (HEMC)), and rural (Pingyuan county (PYC)), using Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS).

RESULTS

The concentrations of total VOCs (TVOCs) at the GETDD, HEMC and PYC sites were 352.5, 129.2 and 75.1 ppb, respectively. The dominant category of VOCs is nitrogen-containing VOCs (NVOCs, accounting for 43.3% of TVOCs) at GETDD, of which C₄H₁₁N (m/z⁺ = 74.10, butyl amine) was the predominant chemical species (80.5%). In contrast, oxygenated VOCs (OVOCs) were the most abundant at HEMC and PYC, accounting for 60.2% and 64.1% of the total VOCs, respectively; here, CH₄O (m/z⁺ = 33.026, methanol) was the major compound, accounting for 40.5% of the VOCs at HEMC and 50.9% at PYC. The ratios of toluene to benzene (T/B) were calculated for different measured sites, as the ratios of T/B can reveal source resolution of aromatic VOCs. The average contributions to total ozone formation potentials (OFP) of the total measured VOCs in each area were 604.9, 315.9 and 111.7 μg/m³ at GETDD, HEMC and PYC, respectively; the highest OFP contributors of the identified VOCs were aliphatic hydrocarbons (AlHs) at GETDD, aromatic hydrocarbons (AHs) at HEMC, and OVOCs at PYC.

CONCLUSIONS

OFP assessment indicated that the photochemical pollution caused by VOCs at GETDD was serious, and was also significant in the HEMC region. The dominant VOC OFP groups (AlHs and AHs) should be prioritized for control, in order to help reduce these effects.

Epigenetic response profiles into environmental epigenotoxicant screening and health risk assessment: A critical review

The epigenome may be an important interface between exposure to environmental contaminants and adverse outcome on human health. Many environmental pollutants deregulate gene expression and promote diseases by modulating the epigenome. Adverse epigenetic responses have been widely used for risk assessment of chemical substances. Various pollutants, including trace elements and persistent organic pollutants, have been detected frequently in the environment. Epigenetic toxicity of environmental matrices including water, air, soil, and food cannot be ignored. This review provides a comprehensive overview of epigenetic effects of pollutants and environmental matrices. We start with an overview of the mechanisms of epigenetic regulation and the effects of several types of environmental pollutants (trace elements, persistent organic pollutants, endocrine disrupting chemicals, and volatile organic pollutants) on epigenetic modulation. We then discuss the epigenetic responses to environmental water, air, and soil based on in vivo and in vitro assays. Finally, we discuss recommendations to promote the incorporation of epigenotoxicity into contamination screening and health risk assessment.

Levels of Volatile Carbonyl Compounds in the Atlantic Rainforest, in the City of Rio de Janeiro

When Europeans arrived in America, the Brazilian Atlantic rainforest covered approximately 1,290,000 km². Now, only 8% of the biome's original vegetation remains. One of the largest areas is Tijuca Forest National Park. In this work, the concentrations of 13 carbonyl compounds in an isolated area inside Tijuca Forest, in an urban park with primary and secondary vegetation (Gericinó Natural Park) and in two typical urban areas (Tijuca District and the city of Nilópolis) were determined. The main compounds were formaldehyde and acetaldehyde. The formaldehyde mean concentrations were 0.98 ± 1.00, 1.27 ± 1.67, 3.09 ± 1.60 and 2.33 ± 2.17 μg m^-3 for Tijuca Forest, Gericinó Natural Park, Tijuca District and the city of Nilópolis, respectively. The mean acetaldehyde concentrations were, for the same locations, 0.93 ± 1.05, 2.94 ± 2.54, 2.78 ± 0.91 and 5.48 ± 1.90 μg m^-3. The results indicate that the compounds measured within the forest are transported from the city and that the trees play an important role in removing air pollutants. In contrast, the Gericinó protected area is heavily affected by urban emissions, and its capacity to dilute or absorb pollutants is low because of the sparse vegetation.

Observations of particulate matter, NO2, SO2, O3, H2S and selected VOCs at a semi-urban environment in the Amazon region

This research aims to assess air quality in a transitional location between city and forest in the Amazon region. Located downwind of the Manaus metropolitan region, this study is part of the large-scale experiment GoAmazon2014/5. Based on their pollutant potential, inhalable particulate matter (PM_2.5), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), ozone (O₃), hydrogen sulfide (H₂S), benzene, toluene, ethylbenzene and meta-, orto-, para-xylene (BTEX) were selected for analysis. Sampling took place during the wet season (March-April 2014) and dry season (August-October 2014). The number of forest fires in the surroundings was higher during the dry wet season. Results show significant increase during the dry season in mass concentration (wet: <0.01-10 μg m^-3; dry: 9.8-69 μg m^-3), NH₄⁺ soluble content (wet: 13-125 μg m^-3; dry: 86-323 μg m^-3) and K⁺ soluble content (wet: 11-168 μg m^-3; dry 60-356 μg m^-3) of the PM_2.5, and O₃ levels (wet: 1.4-14 μg m^-3; dry: 1.0-40 μg m^-3), indicating influence of biomass burning emissions. BTEX concentrations were low in both periods, but also increased during the dry season. A weak correlation in the time series of the organic and inorganic gaseous pollutants indicates a combination of different sources in both seasons and NO2 results suggest a spatial heterogeneity in gaseous pollutants levels beyond initial expectations.

Summertime high resolution variability of atmospheric formaldehyde and non-methane volatile organic compounds in a rural background area

On rural background areas atmospheric formaldehyde (HCHO) is important for its abundance and chemical reactivity, directly linked to the tropospheric ozone formation processes. HCHO is also toxic and carcinogenic to humans. Atmospheric HCHO was continuously measured in summer 2016 during 81 days (N = 6722, average: 1.42 ppbv) in a rural background area in Northern Spain, Valderejo Natural Park (VNP) using a Hantzsch fluorimetric system. To better characterize the photochemical processes the database was completed with hourly measurements of 63 Non-Methane Hydrocarbons (NMHC) performed by gas chromatography and other common atmospheric pollutants and meteorological parameters. HCHO mixing ratios were highly correlated with ozone and isoprene. Cloudy and rainy days, with low temperature and radiation, led to low HCHO mixing ratios, with maxima (<2 ppbv) registered around 14 UTC. On days with increased radiation and temperature HCHO maxima occurred slightly later (<6 ppbv, ≈16:00 UTC). During clear summer days with high temperature and radiation, two HCHO peaks were registered daily, one synchronized with the radiation maximum (≈3-4 ppbv, ≈13:00 UTC) and an absolute maximum (<10 ppbv, ≈18:00 UTC), associated with the addition of HCHO coming into VNP due to inbound transport of old polluted air masses. In the ozone episode studied, the processes of accumulation and recharge of ozone and of HCHO ran in parallel, leading to similar daily patterns of variation. Finally, HCHO mixing ratios measured in VNP were compared with other measurements at rural, forested, and remote sites all over the world, obtaining similar values.

Characteristics and health effects of formaldehyde and acetaldehyde in an urban area in Iran

This study reports a spatiotemporal characterization of formaldehyde and acetaldehyde in the summer and winter of 2017 in the urban area of Shiraz, Iran. Sampling was fulfilled according to EPA Method TO-11 A. The inverse distance weighting (IDW) procedure was used for spatial mapping. Monte Carlo simulations were conducted to evaluate carcinogenic and non-cancer risk owing to formaldehyde and acetaldehyde exposure in 11 age groups. The average concentrations of formaldehyde/acetaldehyde in the summer and winter were 15.07/8.40 μg m-3 and 8.57/3.52 μg m-3, respectively. The formaldehyde to acetaldehyde ratios in the summer and winter were 1.80 and 2.43, respectively. The main sources of formaldehyde and acetaldehyde were photochemical generation, vehicular traffic, and biogenic emissions (e.g., coniferous and deciduous trees). The mean inhalation lifetime cancer risk (LTCR) values according to the Integrated Risk Information System (IRIS) for formaldehyde and acetaldehyde in summer and winter ranged between 7.55 × 10-6 and 9.25 × 10-5, which exceed the recommended value by US EPA. The average LTCR according to the Office of Environmental Health Hazard Assessment (OEHHA) for formaldehyde and acetaldehyde in summer and winter were between 4.82 × 10-6 and 2.58 × 10-4, which exceeds recommended values for five different age groups (Birth to <1, 1 to <2, 2 to <3, 3 to <6, and 6 to <11 years). Hazard quotients (HQs) of formaldehyde ranged between 0.04 and 4.18 for both seasons, while the HQs for acetaldehyde were limited between 0.42 and 0.97.

Isoprene Emissions and Ozone Formation in Urban Conditions: A Case Study in the City of Rio de Janeiro

The potential role of isoprene oxidative processes, as well as the possible impact of air pollution on isoprene emissions, are more important in tropical cities, surrounded by rainforests. In this study, the contribution of isoprene to ozone formation was determined considering different scenarios, mainly volatile organic compounds/NO _x (VOC/NO _x ) ratios, and typical atmospheric conditions for the city of Rio de Janeiro, where more than 36% of the urbanized area is covered by vegetation. Ozone isopleths and incremental reactivity coefficients (IR) were evaluated to understand the direct contribution of isoprene to ground-level ozone formation and the negative impact of anthropogenic NO _x emissions on the natural atmospheric balance. Although isoprene accounted for only 2.7% of the total VOC mass, excluding the isoprene concentration from the model reduced the maximum ozone value by 14.1%. The calculated IR coefficient (grams of O₃ formed per gram of added isoprene) was 2.2 for a VOC/NO _x ratio of 8.86.

The synthesis of two long-chain N-hydroxy amino coumarin compounds and their applications in the analysis of aldehydes

Two long-chain N-substituted coumaryl hydroxylamines were synthesized, which can serve as excellent probes for the analysis of various aldehydes.

Role of carbonyls and aromatics in the formation of tropospheric ozone in Rio de Janeiro, Brazil

The ozone in Rio de Janeiro has been in violation of national air quality standards. Among all of the monitoring stations, the Bangu neighbourhood has the most violations of the national standard of 160 μg m(-3) for the years 2012 and 2013. This study evaluated the reactivity of the carbonyls and aromatics in the tropospheric ozone formation processes. The samples were collected between July and October of 2013. Carbonyls were sampled using SiO2 cartridges coated with C18 and impregnated with 2,4-dinitrophenylhydrazine and were analysed by HPLC. Activated carbon cartridges and GC/MS were used to measure the concentration of monoaromatic hydrocarbons. An air quality monitoring station provided the concentrations of the criteria pollutants and the meteorological parameters. Cluster analysis and a Pearson correlation matrix were used to determine the formation of groups and the correlation of the variables. The evaluation of the volatile organic compounds (VOC) reaction with OH radicals and the MIR scale was used to extrapolate the reactivity of VOCs to the ozone formation. The average concentrations obtained were 19.7 and 51.9 μg m(-3) for formaldehyde and acetaldehyde, respectively. The mean concentrations obtained for aromatics were 1.5, 6.7, 1.5, 2.6 and 1.6 μg m(-3) for benzene, toluene, ethyl benzene, m+p-xylene and o-xylene, respectively. The cluster analysis indicated the presence of three similar groups, with one formed by gaseous criteria pollutants, another formed by the meteorological parameters, ozone and fine particles, and the last group formed by the aromatics. For the two reactivity scales evaluated, acetaldehyde and toluene were the main ozone precursors.

Diurnal and seasonal variations of carbonyls and their effect on ozone concentrations in the atmosphere of Monterrey, Mexico

Few studies have been made regarding carbonyl concentrations in Monterrey, México. The Monterrey Metropolitan Area (MMA) has the third largest population in the country and has increasing pollution issues. The concentrations of 10 aldehydes and two ketones were measured in the MMA, in the spring and fall of 2011 and 2012. Formaldehyde (16-42 ppbv) was the most abundant carbonyl, followed by acetaldehyde (5-15 ppbv) and acetone (7-15 ppbv). The concentrations showed marked diurnal trends with maximum values between 10:00 a.m. and 2:00 p.m., when photochemical activity is intense. Thus, secondary production of carbonyls is statistically significant in the city. Biogenic production of several carbonyls, such as 2-butanone, was supported by their mid correlation with solar radiation and low correlation with propionaldehyde, which is mainly emitted by anthropogenic sources. The seasonal variability of the concentrations was observed in the first three samplings, with the highest levels reached in the fall. The rainy conditions during the fourth sampling did not allow comparison. Carbonyl-NOx-O3 analysis was made. Results indicated a carbonyl-sensitive atmosphere, especially during the midday samplings of 10:00 a. m. to 2:00 p.m. and 2:00 p.m. and 6:00 p.m. because of the intense solar radiation during these periods.

IMPLICATIONS

Monitoring of carbonyls in Monterrey, Mexico, was performed to quantify the pollutant concentration in the city's atmosphere. Although primary emission is significantly important, the secondary production of the pollutants, along with ozone production being carbonyl sensitive, indicates that air pollution controls must address the direct sources and the precursors of the pollutants to achieve air quality.

Seasonal variations of monocarbonyl and dicarbonyl in urban and sub-urban sites of Xi'an, China

Seventeen airborne carbonyls including monocarbonyls and dicarbonyls were determined in urban and sub-urban sites of Xi'an, China in three seasons in 2010. In winter, acetone was the most abundant carbonyl in the urban site due to usage of organic solvents in constructions and laboratories and its slower atmospheric removal mechanisms by photolysis and reaction with hydroxyl radical than those of formaldehyde and acetaldehyde. In the sub-urban site, acetaldehyde was the most abundant carbonyl, followed by formaldehyde and acetone. During summer, however, formaldehyde was the most dominant carbonyl in both sites. The photooxidations of a wide range of volatile organic compounds (VOCs) yielded much more formaldehyde than other carbonyls under high solar radiation and temperature. In the urban site, the average concentrations of dicarbonyls (i.e., glyoxal and methyglyoxal) in spring and summer were higher than that in winter. Transformation of aromatic VOCs emitted from fuel evaporation leads to the formation of 1,2-dicarbonyls. A reverse trend was observed in sub-urban sites, as explained by the relatively low abundances and accumulations of VOC precursors in the rural atmosphere during warm seasons. Moreover, cumulative cancer risk based on measured outdoor carbonyls (formaldehyde and acetaldehyde) in Xi'an Jiaotong University and Heihe was estimated (8.82 × 10(-5) and 4.96 × 10(-5), respectively). This study provides a clear map on the abundances of carbonyls and their source interpretation in the largest and the most economic city in Northwestern China.

Characteristics of atmospheric non-methane hydrocarbons in Foshan City, China

Foshan is the most air-polluted city in Pearl River Delta. Non-methane hydrocarbons (NMHCs) were investigated for the first time in Foshan in winter 2008. Ethene, ethane, ethyne, propane, i-pentane, and toluene were the most abundant hydrocarbons and observed to be higher in Foshan than those in many other cities in China. Different from other cities, ethene and ethane were observed to be the two highest compounds in Foshan. Generally, the most abundant hydrocarbons showed high mixing ratios in the morning (0930-1030 hours), decreased to the lowest level in the afternoon (1430-1530 hours), and increased to higher value in the evening (1930-2030 hours). But i-pentane exhibited a different diurnal pattern with the highest level (13.4 ± 5.8 ppbv) in the afternoon, implying the acceleration of solvent evaporation resulting from higher temperature. Correlation coefficients (R(2) = 66% for n = 6 at 95% confidence level) of the individual hydrocarbons with ethyne and i-pentane indicated vehicular emissions were the main sources of ethene, propene, i-butene, isoprene, benzene and toluene, while gasoline evaporation was responsible for n-pentane, n-hexane, and n-heptane. The good correlation of most of the hydrocarbons with ethyne, indicating vehicular emissions, were the main sources of NMHCs. B/T ratio was 0.36 ± 0.06, implying vehicular emissions acted as the major contributors as well as additional emissions of toluene emitted from solvent usage. According to investigation, it also suggested that LPG leakage was the main source of propane, while NG leakage was responsible for ethane in Foshan City.

Carbonyl compounds and BTEX in the special rooms of hospital in Guangzhou, China

The occurrence of carbonyl compounds and benzene, toluene, ethylbenzene and xylenes (BTEXs) was assessed in the indoor and outdoor air of a hospital in Guangzhou, China. The pharmacy room, the preparing traditional Chinese medicine room, the supply room (where the medical appliances are disinfected), the laundry and the garbage room were selected as sampling sites. Acetaldehyde (ranging from 4.56 to 66.8 microg m(-3)) was in all samples the most abundant among the 18 carbonyls detected, and toluene (ranging from 33.5 to 264 microg m(-3)) among the BTEXs. The indoor/outdoor (I/O) concentration ratios of BTEXs in the morning were always >1.0, and close to 1.0 or slightly <1.0 in the afternoon, while the concentration ratios of carbonyls in the afternoon showed large variation. These ratios demonstrate the significance of outdoor emissions that deteriorate the indoor air quality at the various rooms of the hospital. The possible sources of BTEXs and carbonyls in these rooms are discussed with the use of specific ratios and with the use of statistical methods, like principal components analysis.

Pattern of volatile aldehydes and aromatic hydrocarbons in the largest urban rainforest in the Americas

Atmospheric concentrations of aldehydes and monoaromatic hydrocarbons were determined in Tijuca Forest, the largest urban tropical forest in the Americas. The forest is a protected area, surrounded by the city of Rio de Janeiro. Data were also obtained in a commercial and a residential area for comparison. A total of 160 aldehyde samples and 60 BTEX (benzene, toluene, ethyl-benzene and xylenes) samples were collected from four locations between January and August of 2008. The aldehydes were collected using C18 resin cartridges coated with 2,4-dinitrophenylhydrazine and analyzed by high performance liquid chromatography (HPLC) with a diode array UV-Vis detector, while the BTEX samples were collected using tubes of coconut charcoal, which were then extracted with dichloromethane and analyzed by gas chromatography (GC). Within Tijuca Forest, formaldehyde and acetaldehyde levels were in the range of <detection limit - 5.09 ppbV and <detection limit - 4.08 ppbV, respectively. Formaldehyde concentrations strongly correlated with temperature and solar radiation. The different ratios for formaldehyde and acetaldehyde concentrations in the forest and in the urban sites clearly suggested that carbonyl levels within the forest might have an important contribution from biogenic sources. BTEX concentrations in the forest were very low, showing that the forest acted as a sink for many pollutants. Toluene/benzene ratios in the forest were also lower than in the city, which may be attributed to the faster photochemical oxidation of toluene. These observations were indicators of the low impact of the urban area on the studied forest.

Comparative study of automotive, aircraft and biogenic emissions of aldehydes and aromatic compounds

Air samples were collected in three well characterized locations in the city of Rio de Janeiro, Brazil: downtown, the idle and taxi way areas of the national airport and an urban forest, where the main emissions are from vehicular, aircraft and biogenic sources, respectively. Aldehydes and BTEX concentrations show a characteristic profile which may be attributed to the emission sources. Formaldehyde/acetaldehyde ratios, in the early morning, were 1.39, 0.62 and 2.22 in downtown, airport and forest, respectively. Toluene/benzene ratios, for downtown, airport and forest areas, were 1.11, 1.82 and 1.06, respectively. The results show that the impact of the urban emissions on the forest is negligible as well as the impact of aircraft emissions over the urban area.