Anthropogenic Volatile Organic Compounds Research Articles

Sources Profiles of Anthropogenic Volatile Organic Compounds from Typical Solvent Used in Chengdu, China

Volatile organic compound (VOC) source profiles of Chengdu were established based on stack and fugitive emission source samples by field measurements. A total of 54 VOC samples collected from the petrochemical industry, printing, wood-based panel manufacturing, wood furniture coating, and shoemaking industry were measured. A total of 80 VOC species were classified into five categories, including aromatic hydrocarbons, halocarbons, and oxygenated VOCs (OVOCs). Combined with the results of measurement and literature surveys, the sector-specific emission factors conducted from the solvent-using consumption varied range from 0.35 to 1.45 Kg VOCs per Kg of solvent-use consumption (Kg·Kg−1). Ethanol and m-xylene were predominant species of solvent used in the printing industries. Urea-formaldehyde resin was widely used as an adhesive in more than 80% of wood-based panels in Chengdu; a lot of formaldehyde and other harmful substances were directly discharged into the environment without any treatment. The evaluation of the source reactivity for various VOC emission sources were conducted. Aromatic hydrocarbon was found to be the most abundant component in the wood furniture coating and shoemaking industries. The ozone formation potential (OFP) for the unit mass of VOCs emissions was the highest for m/p-xylene (25.12%). The secondary organic aerosol (SOA) formation was also calculated, and the aromatic contributed 82.16% for almost all of the SOA formation. Furthermore, several proposals were made to reduce or regulate VOC emissions in Chengdu.

A high spatiotemporal resolution anthropogenic VOC emission inventory for Qingdao City in 2016 and its ozone formation potential analysis

Accurate and gridded emission inventories are crucial for better air quality modeling and air pollution policy making. As the economic center of the Shandong province and part of the first batch of open coastal cities in China, Qingdao has been frequently plagued by volatile organic compound (VOC) pollution along with its rapid economic development and urbanization in recent years. In this study, a high spatiotemporal resolution VOC emission inventory for Qingdao was established for the year 2016 using updated source-specific emission factors and the latest activity data for different sources. The anthropogenic sources considered in this study are classified into seven major sources and 46 subcategories. The results indicated that a total of 151.5 kt of VOCs were emitted in Qingdao in 2016. The three largest emission sources, industrial process, on-road mobile, and solvent use sources accounted for 49.9% 20.1%, and 14.1% of the total VOC emissions, respectively. Spatially, the Huangdao District (57.9 kt), the Chengyang District (15.4 kt), and Pingdu City (15.1 kt) were the top three emitters of VOCs. The high concentration of VOCs was mainly distributed in the central areas of Qingdao city and the emissions distribution was highly consistent with its road network. The maximum monthly VOC emissions occurred in June (14.4 kt) and the minimum monthly VOC emissions occurred mainly in February (9.5 kt). The uncertainties in the emission inventory were quantified using a Monte Carlo simulation provided by the Oracle Crystal Ball software. There exist relatively high uncertainties in the on-road mobile (-84.79%, 252.07%), biomass burning (-65.38%, 134.77%) and industrial process (-36.08%, 133.62%) sources. For the complicated species and different reaction rates of ozone formation, the control of the amount of VOCs emitted and the highly reactive VOCs are equally important. Based on the emissions of individual VOC species and the corresponding maximum incremental reactivity (MIR), the ozone formation potential (OFP) profiles of Qingdao City were constructed. The results indicated that alkenes/alkynes and aromatics contributed the most to the OFP and that m/p-xylene, ethylene, propylene, formaldehyde, toluene, trans-2-butene, cis-2-butene, 1-butene, o-xylene, and 1-pentene were the top 10 individual VOC species contributing to the OFP. The contribution of industrial process and on-road mobile sources accounted for 37.5% and 24.5% of the total OFP in Qingdao City, respectively. Both the large VOC emission and OFP indicate that the focus of VOC emission control should be on industrial process and on-road mobile sources in Qingdao City.

Two decades of ozone standard exceedances in Santiago de Chile

A drastic decline of 2.4 ppbv decade−1 in the ozone mixing ratio has been measured in Santiago de Chile during the 2000s. Subsequently, in the 2010s, ozone trends stabilized in downtown and showed upward trends in eastern Santiago. The number of days with an 8-h average ozone mixing ratio above 61 ppbv, deemed harmful to health according to Chilean legislation, has declined significantly both in western and central Santiago. However, in eastern Santiago, one finds a 2010–2018 decade average of 43 days per year above recommended levels. Also, at a Receptor Site located ~ 70 km downwind from Santiago, this number rose to up to 3 months per year. A common denominator for the last two decades has been a steady increase in both gasoline and diesel-powered private cars. In the 2010s, the ozone weekend effect was frequently noted, providing evidence that the ozone formation regime in Santiago is VOC-limited. Nitrogen oxides and carbon monoxide (a proxy of anthropogenic VOCs) have increased steadily since 2014 in a relatively constant CO-to-NOx ratio. Therefore, we propose that primary emissions of NOX and VOCs from motor vehicle exhaust have remained as the main driver of the photochemical air pollution in Santiago as well as explaining the weekly variation. Santiago, like other megacities in the world, faces several challenges associated with increasing urbanization as well as the effects of climate change. An increasing population, growth in private car use, and urban sprawl have contributed to maintain high levels of ozone. New threats such as increasing temperatures observed in the central valleys of Chile, along with more frequent occurrences of heat waves, whose number has doubled in the last decade, will require a different approach to manage ozone pollution during the next decade. Santiago will not meet its own goals in the upcoming years without implementing robust, scientifically sound, and cost-effective strategies designed specifically to tackle photochemical pollution.

A multi-scale model analysis of ozone formation in the Bangkok Metropolitan Region, Thailand

Abstract Over the last three decades, Thailand's rapid industrialization and urbanization have led to an impact on urban air quality. A majority of the country's development has occurred within and around Bangkok (BKK), the capital city of Thailand, and the Bangkok Metropolitan Region (BMR). Since 1995, the BMR has experienced air quality degradation, in particular, enhanced ozone (O3) due to a combination of the local increase in emissions from accelerated growth in automotive and industrial activities, local meteorology including strong solar radiation, high temperature and high humidity, and potential long-range effects of regional transport from China. To investigate the O3 formation in the BMR due to the effects of long-range transport and local meteorology feedbacks, we perform a multi-scale simulation with the Weather Research and Forecasting model with Chemistry (WRF-Chem) during the O3 season (January to March), 2010; since O3 mixing ratio exceedances in the BMR occur primarily during this period The results in this study indicate the significance of China's emission reductions on the regional-scale and the local-scale pollution, as far as the BMR region and southern Thailand. Applying China's oxide of nitrogen (NOx)-only emission controls, generally, enhance the domain-wide monthly-average peroxyacetyl nitrate (PAN) and O3 in the regional scale, in the order of ~1–7% and ~1–5%, respectively, while those in the local scale are ~ 0.2–6% and ~0.1–5% compared with the baseline simulation. However, the increases in PAN and O3 are mitigated by 40% China's Volatile Organic Compound (VOC) reduction along with 40% NOx reduction. The results, supported by an indicator analysis, suggest that northern and eastern China, northern and central Thailand and the BMR, are likely VOC-limited during the O3 season. Since the BMR is VOC-limited regime, controlling anthropogenic VOC emissions will show more benefit to control O3 than controlling NOx-only emissions. Other factors that influence on O3 levels in the BMR are biogenic VOC emissions from the Tenasserim range and land- and sea-breeze circulations that recirculate and disperse pollutants along the coastal areas.

Numerical Sensitivity Tests of Volatile Organic Compounds Emission to PM2.5 Formation during Heat Wave Period in 2018 in Two Southeast Korean Cities

A record-breaking severe heat wave was recorded in southeast Korea from 11 July to 15 August 2018, and the numerical sensitivity simulations of volatile organic compound (VOC) to secondarily generated particulate matter with diameter of less than 2.5 µm (PM2.5) concentrations were studied in the Busan and Ulsan metropolitan areas in southeast Korea. A weather research and forecasting (WRF) model coupled with chemistry (WRF-Chem) was employed, and we carried out VOC emission sensitivity simulations to investigate variations in PM2.5 concentrations during the heat wave period that occurred from 11 July to 15 August 2018. In our study, when anthropogenic VOC emissions from the Comprehensive Regional Emissions Inventory for Atmospheric Transport Experiment-2015 (CREATE-2015) inventory were increased by approximately a factor of five in southeast Korea, a better agreement with observations of PM2.5 mass concentrations was simulated, implying an underestimation of anthropogenic VOC emissions over southeast Korea. The simulated secondary organic aerosol (SOA) fraction, in particular, showed greater dominance during high temperature periods such as 19–21 July, 2018, with the SOA fractions of 42.3% (in Busan) and 34.3% (in Ulsan) among a sub-total of seven inorganic and organic components. This is considerably higher than observed annual mean organic carbon (OC) fraction (28.4 ± 4%) among seven components, indicating the enhancement of secondary organic aerosols induced by photochemical reactions during the heat wave period in both metropolitan areas. The PM2.5 to PM10 ratios were 0.69 and 0.74, on average, during the study period in the two cities. These were also significantly higher than the typical range in those cities, which was 0.5–0.6 in 2018. Our simulations implied that extremely high temperatures with no precipitation are significantly important to the secondary generation of PM2.5 with higher secondary organic aerosol fraction via photochemical reactions in southeastern Korean cities. Other possible relationships between anthropogenic VOC emissions and temperature during the heat wave episode are also discussed in this study.

Evaluating the effectiveness of multiple emission control measures on reducing volatile organic compounds in ambient air based on observational data: A case study during the 2010 Guangzhou Asian Games

Volatile organic compounds (VOCs) play a crucial role in modulating air pollution by ozone and fine particles, particularly in urban areas. While in recent years short-term intervention actions for better air quality during big events in China did present good opportunities to examine the effectiveness of control measures in reducing anthropogenic VOCs emission, it is highly challenging to interpret the real effect of a specific control measure based on field monitoring data when a cocktail of control measures were adopted. Here we took the air quality intervention actions during the 16th Asian Games (AG) in Guangzhou as a case study to explore the impact of short-term multiple measures on VOCs reduction. The average mass concentrations of VOCs decreased by 52–68% during the AG. These percentages could not reflect emission reduction rates as the concentration might be also heavily impacted by dispersion conditions. Diagnostic ratios, such as methyl tert-butyl ether to carbon monoxide (MTBE/CO) and i-pentane/CO, decreased by over 60% during the AG, suggesting a substantial reduction in gasoline related emissions. A method linking emission reduction rates of two sources with their contribution percentages before and during the AG by using a receptor model was further formulated. With the available reduction rate of 34% for vehicular exhaust obtained during the traffic restriction drill in our previous study, VOCs emissions from gasoline evaporation and solvent use reduced by 45.7% and 13.6% during the AG, respectively. Total VOCs emissions decreased by 25.3% on average during the AG, and the emission control of vehicular exhaust, oil evaporation, and solvent use accounted for 17.0%, 6.3% and 2.0% of total VOCs emission reduction, respectively. This study presented an observed-based method with diagnostic/quantitative approaches to single out the effectiveness of each control measures in reducing VOCs emissions.

Intraday and interday variations of 69 volatile organic compounds (BVOCs and AVOCs) and their source profiles at a semi-urban site

To study the intraday and interday patterns and possible sources of volatile organic compounds (VOCs), 6-h active sampling was performed in April, May, June, July, and August 2017 and in January 2018 in a semi-urban site in Bolu, Turkey. Totally 69 VOCs having biogenic (BVOCs, i.e., isoprene, monoterpenes and oxygenated VOCs) and anthropogenic origins (AVOCs) were examined. Fifty-four of sixty-nine analyzed VOCs could be detected. Decanal followed by benzaldehyde, benzene, phenol, and toluene were detected as the leading anthropogenic VOCs whereas alpha-pinene and hexanal were the dominant biogenic VOCs. There was a decrease in concentrations of most of the VOCs in January and April when light intensity and temperature were relatively low. Atmospheric levels of total biogenic VOCs exceeded that of anthropogenic VOCs in all months except for January and April. Dependence of biogenic VOC emissions on the light intensity, temperature and the increase in leaves were considered to be effective in their higher levels in summer and daytime periods. The daytime anthropogenic VOCs concentrations were higher than the nighttime anthropogenic VOCs probably due to intense vehicle traffic during working hours and/or increased volatilization from their sources at elevated temperatures. The VOCs that significantly and negatively correlated with ozone were evaluated as effective BVOCs in the ozone formation while the maximum incremental reactivity (MIR) method gave the contribution of AVOCs. Positive Matrix Factorization (PMF) was applied for the source apportionment. G score graphs and G score pollution roses were also used to identify possible sources of investigated VOCs. Solvent evaporation, gasoline-powered vehicle emissions, fossil fuel (residential heating), biogenic (hornbeam, grass, oak, beech) emissions, diesel/domestic activities and forested city atmosphere were identified as the possible VOC sources in the study area.

Contrasting trends of PM2.5 and surface-ozone concentrations in China from 2013 to 2017.

Although much attention has been paid to investigating and controlling air pollution in China, the trends of air-pollutant concentrations on a national scale have remained unclear. Here, we quantitatively investigated the variation of air pollutants in China using long-term comprehensive data sets from 2013 to 2017, during which Chinese government made major efforts to reduce anthropogenic emission in polluted regions. Our results show a significant decreasing trend in the PM2.5 concentration in heavily polluted regions of eastern China, with an annual decrease of ∼7% compared with measurements in 2013. The measured decreased concentrations of SO2, NO2 and CO (a proxy for anthropogenic volatile organic compounds) could explain a large fraction of the decreased PM2.5 concentrations in different regions. As a consequence, the heavily polluted days decreased significantly in corresponding regions. Concentrations of organic aerosol, nitrate, sulfate, ammonium and chloride measured in urban Beijing revealed a remarkable reduction from 2013 to 2017, connecting the decreases in aerosol precursors with corresponding chemical components closely. However, surface-ozone concentrations showed increasing trends in most urban stations from 2013 to 2017, which indicates stronger photochemical pollution. The boundary-layer height in capital cities of eastern China showed no significant trends over the Beijing–Tianjin–Hebei, Yangtze River Delta and Pearl River Delta regions from 2013 to 2017, which confirmed the reduction in anthropogenic emissions. Our results demonstrated that the Chinese government was successful in the reduction of particulate matter in urban areas from 2013 to 2017, although the ozone concentration has increased significantly, suggesting a more complex mechanism of improving Chinese air quality in the future.

The abundance and inter-relationship of atmospheric peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), O3, and NOy during the wintertime in Beijing, China

Although atmospheric peroxyacetyl nitrate (PAN) and O3 have been extensively measured in Beijing during the summertime, the abundances of PAN, peroxypropionyl nitrate (PPN) and the total odd-reactive nitrogen budget (NOy) and their inter-relationship have been studied comparatively less in the winter. Here we measured atmospheric PAN, PPN, O3, NOx, and NOy in Beijing from Nov. 2012 to Jan. 2013. Compared with our previous results in the summertime, much lower levels were observed in the winter, with the mean and maximum values of 311.8 and 1465 pptv for PAN, 52.8 and 850.6 pptv for PPN, and 11.6 and 36.7 ppbv for O3. In contrast, high levels were found as 94.2 and 374.9 ppbv for NOy, with a major constituent of NOx (75.9%). The source to the west and northwest made the significant contribution to the relatively high O3 concentrations during nighttime. PAN concentrations were highly related with the PAN-rich air mass transported from the southeast during the nighttime, whereas predominated by local photochemical production during the daylight. The distributions of NOx and NOy were dominated by local emission and photochemical production during daylight but also influenced by air masses transported from south direction during nighttime. Significant positive correlation (R2 = 0.9, p < 0.0001) between PAN and PPN with a slope (∆PPN/∆PAN) of 0.17 indicated that anthropogenic volatile organic compounds (AVOCs) dominated the photochemical formation of PANs in Beijing, and the independent relationship between the PPN/PAN ratio and PAN (>500 pptv) implied a steady state between PAN and PPN achieving rapidly in the polluted air masses. Negative correlation and slopes between PAN and O3 likely resulted from their weak photochemical productions in the winter, coupled with the large NO sources which acted as a local sink for O3, but much less so for PAN due to its enhanced thermal stability under low temperature.

An explicit study of local ozone budget and NOx-VOCs sensitivity in Shenzhen China

In China, a significant reduction in primary pollution has been observed due to the Clean Air Action since 2013, and ozone pollution has become increasingly prominent over the past years. Pearl River Delta (PRD) is one of the most successful regions concerning primary pollution control, while is suffering from severe ozone pollution during autumn. In this study, we present a field campaign in Shenzhen, a megacity in PRD, in October 2018 with measurements of ozone and photochemical precursors. These observational data are helpful to analyze the local ozone budget and its sensitivity to precursors with the help of an observation-based model (RACM2-LIM1). The observed ozone concentration was up to 121 ppbv during a photochemical episode from 1 to 8 October, when intensive ozone formation up to tens of ppbv/h was found. Ozone vertical measurement indicates the fast ozone production is happening throughout the planetary boundary layer (PBL), which is an important source of morning ozone increase resulting in ozone pollution. An explicit case study is performed to reveal the diurnal feature of instantaneous ozone production rate (P(Ox)) and accumulative P(Ox) based on the O3-NOx-VOC sensitivity, ROx radical primary production rate (P (ROx)), and LN/Q for three cases including ozone pollution and attainment periods. Results show that nitrogen oxides (NOx = NO + NO2) reduction have positive and negative impact on local ozone production from one pollution episode to the other, which indicates the complexity of O3-precursors sensitivity and difficulty to control ozone pollution in Shenzhen. Finally, comparison among measurements in other campaigns provides additional evidence on local ozone production sensitivity on NOx and anthropogenic volatile organic compounds (AVOCs) with respect to a temporal and spatial change. The NOx reduction in Shenzhen has led to higher ozone production from 2015 to 2018 given the nearly constant VOC. However, the ozone mitigation would be benefit from further NOx reduction in the conditions of 2018.

Waste biomass-derived oxygen and nitrogen co-doped porous carbon/MgO composites as superior acetone adsorbent: Experimental and DFT study on the adsorption behavior

The amount of anthropogenic volatile organic compounds (VOCs) emission keeps increasing worldwide, and it urges the development of VOC emission reduction technology. Efficient and environmentally friendly adsorption technology is receiving more interest, and carbon-based materials have attracted enormous attention for VOC capture. However, the poor adsorption capacity and cycling stability still hinder their application. Moreover, the mechanism of adsorption behavior between functionalized carbon surfaces and VOCs has not been investigated in detail. Herein, we report a sustainable and cost-effective method for the anchoring of the MgO nanoparticle onto O/N co-doped porous carbon derived from waste biomass (denoted as MgO@ONPC). The optimized 7%MgO@ONPC composite exhibited an exceedingly high acetone adsorption capacity (859 mg g−1 at 25 °C, 18 kPa) and excellent cycling stability (95.2% capacity retention over 10 cycles). Acetone dynamic breakthrough tests showed that the adsorption capacity of 7%MgO@ONPC composite at 10% breakthrough level (10% BT) and 100% BT was 384 and 508 mg g−1, respectively (in terms of PC: 3.9 × 10−3 and 5.2 × 10−2 mol kg−1 Pa−1, respectively). Isotherm model fitting and quantum chemistry calculation studies indicated O/N functional groups and MgO nanoparticles can significantly improve the acetone monolayer adsorption at low relative pressures due to hydrogen bonds and electrostatic interaction. Highly active MgO nanoparticles and pore structure characteristics are found to be determinative factors for acetone adsorption at high relative pressure.

Understanding the sources and spatiotemporal characteristics of VOCs in the Chengdu Plain, China, through measurement and emission inventory

In order to evaluate the volatile organic compounds (VOCs) pollution characteristics in Chengdu and to identify their sources, ambient air sample collection and measurement were conducted at 28 sampling sites covering all districts/counties of Chengdu from May 2016 to January 2017. Meanwhile, a county-level anthropogenic speciated VOCs emission inventory was established by “bottom-up” method for 2016. Then, a comparison was made between the VOCs emissions, spatial variations, and source structures derived from the measurement and emission inventory. Ambient measurements showed that the annual average mixing ratios of VOCs in Chengdu were 57.54 ppbv (12.36 to 456.04 ppbv), of which mainly dominated by alkanes (38.8%) and OVOCs (22.0%). The ambient VOCs in Chengdu have distinct spatiotemporal characteristics, with a high concentration in January at the middle-northern part of the city and a low concentration in September at the southwestern part. The spatial distribution of VOCs estimated by the emission inventory was in good agreement with ambient measurements. Comparison of individual VOCs emissions indicated that the emissions of non-methane hydrocarbon species agreed within ±100% between the two methods. Both positive matrix factorization (PMF) model results and emission inventory showed that vehicle emissions were the major contributor of anthropogenic VOCs in Chengdu (31% and 37%), followed by solvent utilization (26% and 27%) and industrial processes (23% and 30%). The large discrepancies were found between the relative contribution of combustion sources, and the PMF resolved more contributions (20%) than the emission inventory (6%). Overall, this study demonstrates that measurement results and emission inventory were in a good agreement. However, to improve the reliability of the emission inventory, we suggest significant revision on source profiles of oxygenated volatile organic compounds (OVOCs) and halocarbons, as well as more detailed investigation should be made in terms of energy consumption in household.

Anthropogenic and biogenic hydrophobic VOCs detected in clouds at the puy de Dôme station using Stir Bar Sorptive Extraction: Deviation from the Henry's law prediction

Abstract Cloud droplets are able to trap many gaseous compounds and represent a very reactive media in the atmosphere. However, phase-partitioning of Volatile Organic Compounds (VOCs) between gaseous phase (interstitial air) and atmospheric liquid phase (cloud droplets) is still poorly characterized. In the present work, air samples and cloud water were collected simultaneously and hydrophobic organic compounds from anthropogenic and biogenic origins were quantified in order to evaluate their air/water partitioning. For this, cloud events were sampled at the puy de Dome station (PUY). A new analytical approach was optimized to explore dissolved VOCs in the aqueous phase by Stir Bar Sorptive Extraction (SBSE) and gaseous samples were collected using sorbent tubes. All samples were analyzed by Thermal Desorption (TD) Gas Chromatography (GC) coupled with Mass Spectrometry (MS). Extraction efficiencies by SBSE vary between 22% and 97% and the detection limit of VOCs in aqueous cloud samples lies between 1.0 and 8.7 ng L−1. Experimental partitioning is evaluated towards the theoretical one described by the Henry's Law constants. Our results show that observed concentrations of hydrophobic VOCs are supersaturated by a factor of 10–103 in comparison with Henry's law equilibrium. Calculations have been performed to evaluate the potential role of adsorption at the air/water interface and of sorption with non-dissolved organic carbon. However, the supersaturation in the cloud droplets requires more laboratory experiments to understand processes at the air/water interface and constrain cloud chemistry models.

Estimation of Anthropogenic VOC Source Area around Tokyo Bay: Results from the VOC Concentration Changes in Relation to Wind Direction

Estimation of Anthropogenic VOC Source Area around Tokyo Bay: Results from the VOC Concentration Changes in Relation to Wind Direction

Isomeric Identification of Particle-Phase Organic Nitrates through Gas Chromatography and Time-of-Flight Mass Spectrometry Coupled with an Electron Capture Negative Ionization Source.

Organic nitrates (ONs) are an important component of secondary organic aerosols that play significant roles in atmospheric chemical processes such as ozone formation and as a reservoir of nitrogen oxides (NOx). However, hindered by the availability of analytical techniques, characteristics of ON molecules remain unclear in regions influenced by anthropogenic volatile organic compounds (VOCs) and pollution. In this study, we achieved isomeric identification of particle-phase ONs in such regions. Using gas chromatography and time-of-flight mass spectrometry with an electron capture negative ionization source, we established a systematic procedure for screening unknown ONs in fine particulate matter (PM) collected in Beijing based primarily on the characteristic fragment ions of NO2- and [M-NO2]-/[M-NO2-H2]-. We found 78 ON candidates, 12 of which were confirmed using synthesized standards. Seventy-three of these detected ONs might originate from anthropogenic VOC precursors especially alkenes. Significantly, we observed two isomers generated from straight-chain 1-alkenes, namely, 2-hydroxy-1-nitrate and 1-hydroxy-2-nitrate. The signal ratios of the two isomers suggested that these hydroxy nitrates are mainly produced photochemically rather than through nighttime reactions. This study provides a promising method for identifying ONs in atmospheric PM and elucidating their formation pathways.

Effect of NO&amp;lt;sub&amp;gt;&amp;lt;i&amp;gt;x&amp;lt;/i&amp;gt;&amp;lt;/sub&amp;gt; on 1,3,5-trimethylbenzene (TMB) oxidation product distribution and particle formation

Abstract. Secondary organic aerosol (SOA) represents a significant fraction of the tropospheric aerosol and its precursors are volatile organic compounds (VOCs). Anthropogenic VOCs (AVOC) dominate the VOC budget in many urban areas with 1,3,5-trimethylbenzene (TMB) being among the most reactive aromatic AVOCs. TMB formed highly oxygenated organic molecules (HOMs) in an NOx-free environment, which could contribute to new particle formation (NPF) depending on oxidation conditions where elevated OH oxidation enhanced particle formation. The experiments were performed in an oxidation flow reactor, the Go:PAM unit, under controlled OH oxidation conditions. By addition of NOx to the system we investigated the effect of NOx on particle formation and on the product distribution. We show that the formation of HOMs, and especially HOM accretion products, strongly varies with NOx conditions. We observe a suppression of HOM and particle formation with increasing NOx/ΔTMB ratio and an increase in the formation of organonitrates (ONs) mostly at the expense of HOM accretion products. We propose reaction mechanisms and pathways that explain the formation and observed product distributions with respect to oxidation conditions. We hypothesise that, based on our findings from TMB oxidation studies, aromatic AVOCs may not contribute significantly to NPF under typical NOx/AVOC conditions found in urban atmospheres.

Mechanistic study of the formation of ring-retaining and ring-opening products from the oxidation of aromatic compounds under urban atmospheric conditions.

Aromatic hydrocarbons make up a large fraction of anthropogenic volatile organic compounds and contribute significantly to the production of tropospheric ozone and secondary organic aerosol (SOA). Four toluene and four 1,2,4-trimethylbenzene (1,2,4-TMB) photooxidation experiments were performed in an environmental chamber under relevant polluted conditions (NO x ~ 10ppb). An extensive suite of instrumentation including two proton-transfer-reaction mass spectrometers (PTR-MS) and two chemical ionisation mass spectrometers ( CIMS and I- CIMS) allowed for quantification of reactive carbon in multiple generations of hydroxyl radical (OH)-initiated oxidation. Oxidation of both species produces ring-retaining products such as cresols, benzaldehydes, and bicyclic intermediate compounds, as well as ring-scission products such as epoxides and dicarbonyls. We show that the oxidation of bicyclic intermediate products leads to the formation of compounds with high oxygen content (an O : C ratio of up to 1.1). These compounds, previously identified as highly oxygenated molecules (HOMs), are produced by more than one pathway with differing numbers of reaction steps with OH, including both auto-oxidation and phenolic pathways. We report the elemental composition of these compounds formed under relevant urban high-NO conditions. We show that ring-retaining products for these two precursors are more diverse and abundant than predicted by current mechanisms. We present the speciated elemental composition of SOA for both precursors and confirm that highly oxygenated products make up a significant fraction of SOA. Ring-scission products are also detected in both the gas and particle phases, and their yields and speciation generally agree with the kinetic model prediction.

Compositions, sources and health risks of ambient volatile organic compounds (VOCs) at a petrochemical industrial park along the Yangtze River

Petrochemical industry (PI) is an important emission sector of anthropogenic volatile organic compounds (VOCs). The health impacts of VOCs from PI have caused a wide attention by both scientists and publics. In this study, compositions, sources and health risks of VOCs at a typical petrochemical industrial park along the middle reach of Yangtze River were studied. The total VOC concentrations were in the range of 5.59 to 541 ppbv with a mean value of 54.8 ppbv. Alkanes (41.4 ± 15.7%) were the predominant group, followed by alkenes (19.9 ± 18.3%), OVOCs (14.7 ± 9.26%), halo hydrocarbon (11.2 ± 6.42%), aromatics (8.17 ± 5.08%), and acetylene (4.54 ± 2.80%). Compound-specific health risk results showed that acrolein and 1,3-butadiene had the highest non-carcinogenic risk (expressed by hazard ratio, HR: 22.8) and carcinogenic risk (expressed by lifetime cancer risk, LCR: 6.7 × 10−3), respectively. Positive matrix factorization (PMF) model identified four VOC sources including fuel evaporation, industrial sources, ethylene industry and regional background with the average contributions of 35.6%, 12.0%, 26.5% and 25.9%, respectively. The receptor-originated approach combining the PMF model and conventional methods (HR and LCR) was used to assess the source-specific health risks. The non-cancer risks of four VOC sources were above safe level with regional background contributing most (38.3% or 4.91) to HR. The cancer risks of the four sources were below the tolerable level (<10−4) and regional background also contributed most, with relative contribution of 58.4% (or 10–4.22) to LCR. Our results are conductive to the formulation of countermeasures to reduce human exposure to ambient VOCs at petrochemical industrial parks in China.

Satellite UV-Vis spectroscopy: implications for air quality trends and their driving forces in China during 2005\u20132017

Abundances of a range of air pollutants can be inferred from satellite UV-Vis spectroscopy measurements by using the unique absorption signatures of gas species. Here, we implemented several spectral fitting methods to retrieve tropospheric NO2, SO2, and HCHO from the ozone monitoring instrument (OMI), with radiative simulations providing necessary information on the interactions of scattered solar light within the atmosphere. We analyzed the spatial distribution and temporal trends of satellite-observed air pollutants over eastern China during 2005–2017, especially in heavily polluted regions. We found significant decreasing trends in NO2 and SO2 since 2011 over most regions, despite varying temporal features and turning points. In contrast, an overall increasing trend was identified for tropospheric HCHO over these regions in recent years. Furthermore, generalized additive models were implemented to understand the driving forces of air quality trends in China and assess the effectiveness of emission controls. Our results indicated that although meteorological parameters, such as wind, water vapor, solar radiation and temperature, mainly dominated the day-to-day and seasonal fluctuations in air pollutants, anthropogenic emissions played a unique role in the long-term variation in the ambient concentrations of NO2, SO2, and HCHO in the past 13 years. Generally, recent declines in NO2 and SO2 could be attributed to emission reductions due to effective air quality policies, and the opposite trends in HCHO may urge the need to control anthropogenic volatile organic compound (VOC) emissions.

Spatiotemporal characteristics of ozone pollution and policy implications in Northeast China

The ground-level ozone (O3) pollution has become an emerging air quality issue in China. To effectively mitigate ozone pollution in Northeast China (NEC), this study focuses on its characteristics based on the surface ozone, meteorological data, and Ozone Monitoring Instrument (OMI) satellite data. Statistical methods are applied to analyze the effects of meteorology on O3 pollution. The results show that the area and annual averaged maximum 8-h average O3 concentrations rose from 81.3 to 87.4 μg/m3 during 2015–2018 and the nonattainment days kept increasing. The ground-observed O3 concentrations and OMI ozone vertical column densities (VCDs) displayed the pattern of highs in the southwest and lows the northeast of the NEC region with the exceedance areas mainly located over the Liaoning and Jilin provinces in spring and summer. The long-term series of O3, HCHO and NO2 VCDs averaged over NEC all exhibited annual upward trends. Indicated by the OMI HCHO/NO2 ratio, the seasonal and spatial O3-VOCs-NOx sensitivities in NEC provide the control measure guidance for government agencies. Also the ozone control measure needs to consider the biogenic emissions along with the anthropogenic VOCs emissions due to the vast forest areas and large-scale agricultural production in NEC. The ozone pollution episodes in NEC were correlated with weather conditions of high temperature, low relative humidity, long sunshine duration and southwesterly wind in summer and the impact of the East Asia summer monsoon cannot be ignored. Future investigation into VOCs’ measurements and emission inventories are much needed for ozone pollution control in NEC.