Seasonal, diurnal and nocturnal variations of carbonyl compounds in the semi-urban environment of Orléans, France

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.

Significant contribution of carbonyls to atmospheric oxidation capacity (AOC) during the winter haze pollution over North China Plain

Atmospheric carbonyl compounds play significant roles in the cycling of radicals and have exhibited surprisingly high levels in winter that were well correlated to particulate matter, for which the reason have not been clearly elucidated. Here we measured carbonyl compounds and other trace gasses together with PM2.5 over urban Jinan in North China Plain during the winter. Markedly higher carbonyl concentrations (average: 14.63 ± 4.21 ppbv) were found during wintertime haze pollution, about one to three-times relative to those on non-haze days, with slight difference in chemical composition except formaldehyde (HCHO). HCHO (3.68 ppbv), acetone (3.17 ppbv), and acetaldehyde (CH3CHO) (2.83 ppbv) were the three most abundant species, accounting for ∼75% of the total carbonylson both haze and non-haze days. Results from observational-based model (OBM) with atmospheric oxidation capacity (AOC) indicated that AOC significantly increased with the increasing carbonyls during the winter haze events. Carbonyl photolysis have supplied key oxidants such as RO2 and HO2, and thereby enhancing the formation of fine particles and secondary organic aerosols, elucidating the observed haze-carbonyls inter-correlation. Diurnal variation with carbonyls exhibiting peak values at early-noon and night highlighted the combined contribution of both secondary formation and primary diesel-fuel sources. 1-butene was further confirmed to be the major precursor for HCHO. This study confirms the great contribution of carbonyls to AOC, and also suggests that reducing the emissions of carbonyls would be an effective way to mitigate haze pollution in urban area of the NCP region.

Assessment of atmospheric levels of carbonyls in an urban environment of Argentina

It is well-documented that carbonyl compounds have adverse effects on human health. On the other hand, these oxygenated volatile organic compounds (OVOCs) are precursors of secondary pollutants such as tropospheric ozone or peroxy acetyl nitrate (PAN). In particular, formaldehyde, the simplest carbonyl, is the most abundant carbonyl in the air generated from the degradation of most volatile organic compounds (VOCs). This work presents for the first time the characterization and determination of levels of carbonyl compounds by passive monitoring performed from April-December 2021 in the city of Córdoba, Argentina, the second most populated Mediterranean city located in the center of the country. Annual concentrations, considering the 11 carbonyls measured, were in the range of 0.13-8.75 μgm-3. Formaldehyde and acetaldehyde were the carbonyls detected in the highest annual average concentrations of 4.44 ± 1.75 μgm-3 and 3.85 ± 1.44 μgm-3, respectively. These carbonyls represent a contribution of around 40-57% on total carbonyls measured. Statistical analysis to determine significant differences and Pearson correlations with the meteorological parameters were performed. Spring and summer were found to be the seasons with the highest carbonyl concentration linked to forest fire episodes, especially in springtime. The values for the C1/C2 and C2/C3 ratios showed that sources of carbonyl formation are anthropogenic. In addition, the prop-Equiv concentration was determined, where formaldehyde and acetaldehyde were the main producers of tropospheric ozone. The ozone formation potential (OFP) showed that spring and summer are the seasons where carbonyls contribute to the formation of tropospheric ozone.This study represents a first approach of the carbonyl concentration in the city and of the influence of meteorological parameters on the behavior of carbonyls.

Characteristics, sources and health risk assessment of atmospheric carbonyls during multiple ozone pollution episodes in urban Beijing: Insights into control strategies

Carbonyls have attracted continuous attention due to their critical roles in atmospheric chemistry and their potential hazards to the ecological environment and human health. In this study, atmospheric carbonyls were measured during several ground-level-ozone (O₃) pollution episodes at three urban sites (CRAES, IEP and BJUT) in Beijing in 2019 and 2020. Comparative analysis revealed that the carbonyl concentrations were 20.25 ± 6.91 ppb and 13.43 ± 5.13 ppb in 2019 and 2020 in Beijing, respectively, with a significant spatial trend from north to south, and carbonyl levels in urban Beijing were in an upper-intermediate range in China, and higher than those in other countries reported in the literature. A particularly noteworthy phenomenon is the consistency of carbonyl concentrations with variations in O₃ concentrations. On O₃ polluted days, the carbonyl concentrations were 1.3-1.5 times higher than those on non-O₃ polluted days. Secondary formation contributed more to formaldehyde (FA) and acetaldehyde (AA) on O₃ polluted days, while the anthropogenic emissions were more significant for acetone (AC) on non-O₃ polluted days. Vehicle exhaust and solvent utilization were the main primary contributors to carbonyls. Due to reduced anthropogenic emissions caused by the COVID-19 lockdown and the "Program for Controlling Volatile Organic Compounds in 2020" in China, the contributions of primary emissions to carbonyls decreased in 2020 in Beijing. Human cancer risks to exposed populations from FA and AA increased with elevated O₃ levels, and the risks still remained on non-O₃ polluted days. The residents around the BJUT site might experience relatively higher human cancer risks than those around the other two sites. The findings in this study confirmed that atmospheric carbonyl pollution and its potential human health hazards cannot be ignored in urban Beijing; therefore, more strict control strategies for atmospheric carbonyls are urgently needed to better protect human health in Beijing in the future.

Pollution characteristics and sources of carbonyl compounds in a typical city of Fenwei Plain, Linfen, in summer

Field measurements of atmospheric carbonyl compounds (carbonyls) and essential precursors of O₃ were carried out in the urban area of Linfen City (Linfen) where serious O₃ pollution has occurred in recent years due to its unique terrain. Carbonyls were sampled using an automatic carbonyl sampler in August 2019 to determine their pollution characteristics and sources. An average concentration of ten carbonyls was 27 ± 5.7 μg m^-3 detected using an HPLC-UV system. The concentrations of most detected carbonyls in August were significantly higher than those in the winter months in China. Acetone, formaldehyde and acetaldehyde were the most abundant species, accounting for 73% of all detected carbonyls. Formaldehyde, acetaldehyde, and methacrolein (MACR) were the most significant contributors to OH• reactivity and ozone generation, indicating that these three carbonyls were the key species influencing the production of O₃. The concentrations of formaldehyde, acetaldehyde, and MACR showed similar diurnal variations on most days, with high values during the daytime reaching a peak at 10:00. However, the concentrations of the latter two species varied less than that of formaldehyde during the day. The acetone concentration generally increased continuously from morning to night, with the maximum value around 22:00. The C1/C2 ratio in summer was higher than that in winter. These results indicated that the carbonyls in Linfen were not only affected by anthropogenic sources such as vehicle exhaust but also by secondary photochemical production. The results of formaldehyde source apportionment showed that the contributions of background, primary, and secondary sources to the observed formaldehyde concentration were 27.6%, 36.6%, and 35.8%, respectively. Additionally, this study revealed for the first time that the vertical transport of air masses containing high concentrations of O₃ and NO₃ radicals above the boundary layer could increase the secondary generation of formaldehyde at night in summer.

A sensitive simultaneous detection approach for the determination of 30 atmospheric carbonyls by 2,4-dinitrophenylhydrazine derivatization with HPLC-MS technique and its preliminary application

Atmospheric carbonyls are important precursors of PM_2.5 and ground-level ozone, and some carbonyls are toxic and harmful; thus, it is crucial to obtain accurate information on the ambient levels of carbonyls. However, the detection of carbonyls is difficult due to their relatively higher reactivities and chemical instabilities; therefore, accurate determination of atmospheric carbonyls is important. In this study, an analytical method for atmospheric carbonyls with high concentration or reactivity was developed, the precursor ion of each carbonyl compound was selected, and the declustering potential (DP) and entrance potential (EP) for each precursor ion were optimized. A 2,4-dinitrophenylhydrazine cartridge derivatization-high performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (DNPH-HPLC/APCI-MS) method for the determination of 30 carbonyls was established. The results showed that the linear range of 24 carbonyls was 1.2-600 ng/mL, while other 6 carbonyls was 1.2-300 ng/mL, and the detection limits of 30 carbonyls ranged from 0.092 to 0.947 ng/mL (0.005-0.049 μg/m³ with an ambient air sampling volume of 96 L). The intra-day and inter-day repeatability ranges were 0.55-4.20% and 1.40-12.48%, respectively. A preliminary application of the method was carried out in the urban area of Beijing in spring and summer of 2021, and it was found that the mean total mass concentration of 30 carbonyls was 35.894 μg/m³. This study provided additional concentration information for 14 atmospheric carbonyls, including mono-, di-, oxygen-containing and heterocyclic carbonyls, which accounted for 38% and 35% of the total mass concentration and OH radical reactivities of 30 carbonyls, respectively. This is the first investigation of simultaneous quantitative analysis of multiple atmospheric carbonyls based on commercial standard derivatives. The optimized method could provide more comprehensive information for atmospheric carbonyls and further support research concerning the role of chemical reaction processes and health effects than traditional measuring techniques.

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.

Atmospheric carbonyls in a heavy ozone pollution episode at a metropolis in Southwest China: Characteristics, health risk assessment, sources analysis

Ambient carbonyls were continuously observed in the field during a heavy ozone pollution episode in Chengdu, China from August 4 to August 19, 2019, and the pollution characteristics, atmospheric photochemical reactivity, human health risk, and sources of carbonyls were analyzed. Fifteen carbonyls were quantified with average total mixing ratios of 20.38 ppbv Formaldehyde (9.86 ppbv), acetone (4.41 ppbv), and acetaldehyde (3.57 ppbv) were the three most abundant carbonyls. During the heavy ozone pollution episode, the concentration of carbonyls was found to be higher on pollution days than on the clean days, and relatively higher in the daytime, especially at noon on the pollution days. This was influenced by the intensity of photochemical reactions and precipitation. The "weekend effect" with the concentration of carbonyls was higher on the weekends than on the weekdays was pointed out. Formaldehyde, acetaldehyde and hexaldehyde were the dominant oxidative species during the observation. The carcinogenic and non-carcinogenic risk values of formaldehyde and acetaldehyde were higher on pollution days than on clean days, and these values were higher compared with those of other cities in China and abroad. Long-term exposure to these compounds should therefore be avoided. Diagnostic ratios and correlation analysis together with backward trajectory analysis showed that primary emission and secondary formation accounted 66%-76% and 24%-34% of carbonyls in Chengdu, respectively, with primary emission being the main sources of carbonyls, and carbonyls from the surrounding cities and emission from natural sources also had a significant contribution to the carbonyls in Chengdu.

Pollution Characteristics of Atmospheric Carbonyl Compounds in a Large City of Northern China

To better understand the pollution characteristics and formation mechanisms of atmospheric carbonyl compounds, continuous measurements of carbonyl compounds in Jinan were taken for one month at a sampling frequency of 2 h. The sources, pollution characteristics, and concentration changes of carbonyl compounds during the summers of 2018 and 2020 were compared. The total concentrations of carbonyl compounds were 10.51 ± 0.13 ppbV and 6.30 ± 1.08 ppbV in 2018 and 2020, respectively. In both years, formaldehyde, acetone, and acetaldehyde were the major carbonyls. Diurnal variations and correlation analyses showed that exhaust emissions from motor vehicles during peak traffic periods significantly contributed to the concentrations of carbonyl compounds in Jinan, with formaldehyde exhibiting net production. The ratio of formaldehyde/acetaldehyde (C1/C2) was 2.64 in 2018 and 2.03 in 2020, indicating that carbonyl compounds are jointly affected by anthropogenic sources and photochemical reactions. Master Chemical Mechanism model analyses showed that the formation of formaldehyde in Jinan was controlled by RO + O2 reactions, and formaldehyde was mainly consumed via photolysis and its reaction with the hydroxyl radical. In situ photochemistry can further promote formaldehyde production. The comparison of the reactivities of different carbonyl compounds revealed that formaldehyde, acetaldehyde, butyraldehyde, and propionaldehyde play an important role in hydroxyl radical reactions and ozone generation. Among all the measured carbonyl compounds, benzaldehyde contributed the most to secondary organic aerosols (SOAs). Overall, this study provides new insights into the formation mechanisms of carbonyl compounds as well as their pollution characteristics.

Seasonal Variations of Carbonyls and Their Contributions to the Ozone Formation in Urban Atmosphere of Taiyuan, China

Ambient carbonyls are critical precursors of ozone (O3) and secondary organic aerosols (SOA). To better understand the pollution characteristics of carbonyls in Taiyuan, field samplings were conducted, and 13 carbonyls were detected in an urban site of Taiyuan for the four seasons. The total concentration of carbonyls in the atmosphere was 19.67 ± 8.56 μg/m3. Formaldehyde (7.70 ± 4.78 μg/m3), acetaldehyde (2.95 ± 1.20 μg/m3) and acetone (5.57 ± 2.41 μg/m3) were the dominant carbonyl compounds, accounting for more than 85% of the total carbonyls. The highest values for formaldehyde and acetone occurred in summer and autumn, respectively, and the lowest occurred in winter. The variations for acetaldehyde were not distinct in the four seasons. Formaldehyde and acetone levels increased obviously in the daytime and decreased at night, while acetaldehyde did not show significant diurnal variations. Higher temperature and stronger sunlight intensity could facilitate the photochemical reaction of volatile organic compounds (VOCs) and enhance the O3 levels in summer. Formaldehyde and acetaldehyde contributed 70–95% of carbonyls’ ozone formation potential (OFP) caused by carbonyls with the highest totals of 268.62 μg/m3 and 38.14 μg/m3, respectively. The highest concentrations of carbonyls from south and southwest winds in summer suggest that the coke industries in the southern Taiyuan Basin should be, firstly, controlled for the alleviation of ozone pollution.

Characterizing carbonyl compounds and their sources in Fuzhou ambient air, southeast of China

In recent years, ozone (O₃) concentrations in the southeastern coastal areas of China have shown a gradual upward trend. As precursors and intermediates in the formation of O₃, carbonyl compounds play key roles in the atmospheric photochemical oxidation cycle. To explore the main pollution characteristics of carbonyl compounds in a typical coastal city in southeast China, ambient samples were collected in Fuzhou (the provincial capital of Fujian province, located on the southeast coast of China) and analyzed using high-performance liquid chromatography with ultraviolet detection. The study was continuously carried out at an urban site (Jinjishan) and a suburban site (Gushan) in Fuzhou from May 8 to 20, 2018. The total concentration of 16 carbonyl compounds at the urban site was 15.45 ± 11.18 ppbv, and the total concentration at the suburban site was 17.57 ± 12.77 ppbv. Formaldehyde (HCHO), acetaldehyde, and acetone were the main species detected in the samples, and acetone had the highest concentration among the species detected. The suburban site had a higher formaldehyde/acetaldehyde ratio and lower acetaldehyde/propionaldehyde ratio than the urban site, implying that biogenic sources potentially contributed to the carbonyl compound concentrations at the suburban site. The results of an observation-based model showed that anthropogenic hydrocarbons promoted HCHO production on May 17 at the urban site. Compared to biogenic emissions, anthropogenic activity is a more important source of carbonyl compounds.

Pollution Characteristics of Atmospheric Carbonyls in Urban Linfen in Winter

Atmospheric carbonyls (aldehyde and ketone compounds) can be precursors for ozone and PM2.5, and they play an essential role in atmospheric chemistry. Linfen is a basin between mountains on the east and west, and there are many coking plants on the north and south sides of its urban area. The special topography and unfortunate industrial layout have frequently contributed to serious air pollution in Linfen. In order to investigate the pollution characteristics of atmospheric carbonyls in winter in urban Linfen, the carbonyl compounds were collected from the Municipal Committee site (MC) and the Yaowangtai site (YWT) from 16 to 25 January 2019, and their concentrations were analyzed by a high performance liquid chromatography-ultraviolet detector (HPLC-UV). The results show that formaldehyde, acetaldehyde, and acetone were the most abundant compounds, accounting for more than 70% of the total mass concentration of carbonyls in urban Linfen. Levels of these three carbonyls increased during the morning and evening traffic rush hours. The mass concentration of formaldehyde at both sites reached peak values at around noon (10:00–14:00). In addition, the mass concentrations of formaldehyde, acetaldehyde, and acetone were positively correlated with CO mass concentrations, whereas only formaldehyde and acetaldehyde were positively correlated with temperature. Therefore, atmospheric formaldehyde in urban Linfen’s winter mainly came from vehicle exhaust emissions and the secondary generation of photochemical reactions. Most of the acetaldehyde came from vehicle exhaust emissions, and photochemical reactions also partially contributed to it. For acetone, vehicle exhaust emissions were the main source. In addition, coking industry emissions from Northern Linfen′s Hongtong County may also have contributed to the atmospheric carbonyls in the urban area of Linfen. For the first time, this study found that formaldehyde showed different behavior to acetaldehyde and acetone; that is, the nighttime decrease in formaldehyde mass concentration was greater than that of acetaldehyde and acetone.

Seasonal and diurnal characteristics of carbonyls in the urban atmosphere of Changsha, a mountainous city in south-central China

Seasonal and diurnal variations of carbonyl compounds were investigated in the ambient air of a mountainous city in China, from September 2014 to July 2015. The most abundant carbonyl compounds are formaldehyde, acetaldehyde and acetone, propionaldehyde and methacryladehyde (MACR), which were all measured in most samples. The average concentrations of formaldehyde, acetaldehyde, acetone, propionaldehyde and MACR in the atmosphere in Changsha were broken down into each season: 6.57, 3.29, 3.66, 0.67 and 0.54 μg/m³ respectively during Spring, 14.09, 8.28, 9.02, 1.28 and 0.6 μg/m³, respectively during Summer, 9.24, 5.48, 8.62, 0.73 and 0.62 μg/m³, respectively during Autumn, and 5.88, 4.84, 7.84, 0.87 and 0.26 μg/m³ respectively during Winter. And majority of the species had higher concentration during noon, showing photochemical oxidation and human activities played an important role in diurnal variation. The highest average C1/C2 (formaldehyde/acetaldehyde) ratio was observed in summer (2.10) compared to those (1.33-2.03) in other seasons, implying the photochemical activities had a positive effect on increasing the ratio of C1/C2. In this study, the monthly concentration of formaldehyde produced from isoprene accounts for 4.8%-39.1% of formaldehyde in ambient air. Strong correlation among some carbonyl compounds means that they came from the same sources. Photochemical reaction was the main source of carbonyl compounds in summer and vehicular exhaust (gasoline and diesel engines) in winter. Changsha is not a completely urbanized city and it is rich in vegetation of broadleaf evergreen shrubs. Both atmospheric photochemical reactions and anthropogenic sources, including vehicular exhaust and industrial processes, dominate the levels of carbonyls. The ILTCR and HQ values of formaldehyde and acetaldehyde are 1.23E-04 and 1.34E-05, 2.80E-01 and 1.86E-01, respectively.

Air pollution survey across the western Mediterranean Sea: overview on oxygenated volatile hydrocarbons (OVOCs) and other gaseous pollutants

Despite the Mediterranean Sea basin is among the most sensitive areas over the world for climate change and air quality issues, it still remains less studied than the oceanic regions. The domain investigated by the research ship Minerva Uno cruise in Summer 2015 was the Tyrrhenian Sea. An overview on the marine boundary layer (MBL) concentration levels of carbonyl compounds, ozone (O₃), and sulfur dioxide (SO₂) is reported. The north-western Tyrrhenian Sea samples showed a statistically significant difference in acetone and SO₂ concentrations when compared to the south-eastern ones. Acetone and SO₂ values were higher in the southern part of the basin; presumably, a blend of natural (including volcanism) and anthropogenic (shipping) sources caused this difference. The mean acetone concentration reached 5.4 μg/m³; formaldehyde and acetaldehyde means were equal to 1.1 μg/m³ and 0.38 μg/m³, respectively. Maximums of 3.0 μg/m³ for formaldehyde and 1.0 μg/m³ for acetaldehyde were detected along the route from Civitavecchia to Fiumicino. These two compounds were also present at levels above the average in proximity of petrol-refining plants on the coast; in fact, formaldehyde reached 1.56 μg/m³ and 1.60 μg/m³, respectively, near Milazzo and Augusta harbors; meanwhile, acetaldehyde was as high as 0.75 μg/m³ at both sites. The levels of formaldehyde agreed with previously reported measurements over Mediterranean Sea and elsewhere; besides, a day/night trend was observed, confirming the importance of photochemical formation for this pollutant. According to this study, Mediterranean Sea basin, which is a closed sea, was confirmed to suffer a high anthropic pressure impacting with diffuse emissions, while natural contribution to pollution could come from volcanic activity, particularly in the south-eastern Tyrrhenian Sea region.

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.

Seasonal Trends of Formaldehyde and Acetaldehyde in the Megacity of São Paulo

The Metropolitan Area of São Paulo (MASP) is the largest megacity in South America, with 21 million inhabitants and more than 8 million vehicles. Those vehicles run on a complex fuel mix, with ethanol accounting for nearly 50% of all fuel sold. That has made the MASP a unique case study to assess the impact of biofuel use on air quality. Currently, the greatest challenge in terms of improving air quality is controlling the formation of secondary pollutants such as ozone, which represents the main air pollution problem in the MASP. We evaluated the temporal trends in the concentrations of ozone, its precursors (formaldehyde, acetaldehyde, and NO2), CO, and NO, from 2012 to 2016. Formaldehyde and acetaldehyde concentrations were frequently higher in winter than in other seasons, showing the importance of meteorological conditions to the distribution of atmospheric pollutants in the MASP. We found no clear evidence that the recent growth in ethanol consumption in Brazil has affected acetaldehyde concentrations, which are associated with emissions from ethanol combustion. In fact, the formaldehyde/acetaldehyde ratio remained relatively constant over the period studied, despite the change in the fuel consumption profile in the MASP.

Seasonal and diurnal variations of BTEX compounds in the semi-urban environment of Orleans, France

Atmospheric concentrations of BTEX (benzene, toluene, ethylbenzene and xylene) were measured at a semi-urban site in Orleans, France, from October 2010 to August 2011. Air samples were collected by multi-bed adsorbent tubes. The BTEX concentrations were determined by thermal desorption-gas chromatography-mass spectrometry detector (TD-GC-MSD) technique. The average concentrations of the total measured BTEX during spring, summer, autumn and winter were 724.2, 337.4, 682.3, 823.0ppt, respectively. Maximal values for their diurnal variations usually happened during rush hours in the morning and late afternoon, and the minimal values in the daytime usually happened in around noontime. The diurnal variation of BTEX in four seasons and the correlations between BTEX and NO indicated that vehicular exhaust might be the primary source of BTEX. Benzene was found in relatively high levels and the B/T ratio was significant high in spring, indicating an irregular emission source of benzene other than traffic-related emissions.