Anthropogenic Volatile Organic Compounds Research Articles

Chemical oxidative potential of secondary organic aerosol (SOA) generated from the photooxidation of biogenic and anthropogenic volatile organic compounds

Abstract. Particulate matter (PM), of which a significant fraction is comprised of secondary organic aerosols (SOA), has received considerable attention due to its health implications. In this study, the water-soluble oxidative potential (OPWS) of SOA generated from the photooxidation of biogenic and anthropogenic hydrocarbon precursors (isoprene, α-pinene, β-caryophyllene, pentadecane, m-xylene, and naphthalene) under different reaction conditions (RO2+ HO2 vs. RO2+ NO dominant, dry vs. humid) was characterized using dithiothreitol (DTT) consumption. The measured intrinsic OPWS-DTT values ranged from 9 to 205 pmol min−1 µg−1 and were highly dependent on the specific hydrocarbon precursor, with naphthalene and isoprene SOA generating the highest and lowest OPWS-DTT values, respectively. Humidity and RO2 fate affected OPWS-DTT in a hydrocarbon-specific manner, with naphthalene SOA exhibiting the most pronounced effects, likely due to the formation of nitroaromatics. Together, these results suggest that precursor identity may be more influential than reaction condition in determining SOA oxidative potential, demonstrating the importance of sources, such as incomplete combustion, to aerosol toxicity. In the context of other PM sources, all SOA systems, with the exception of naphthalene SOA, were less DTT active than ambient sources related to incomplete combustion, including diesel and gasoline combustion as well as biomass burning. Finally, naphthalene SOA was as DTT active as biomass burning aerosol, which was found to be the most DTT-active OA source in a previous ambient study. These results highlight a need to consider SOA contributions (particularly from anthropogenic hydrocarbons) to health effects in the context of hydrocarbon emissions, SOA yields, and other PM sources.

Composition of gaseous organic carbon during ECOCEM in Beirut, Lebanon: new observational constraints for VOC anthropogenic emission evaluation in the Middle East

Abstract. The relative importance of eastern Mediterranean emissions is suspected to be largely underestimated compared to other regions worldwide. Here we use detailed speciated measurements of volatile organic compounds (VOCs) to evaluate the spatial heterogeneity of VOC urban emission composition and the consistency of regional and global emission inventories downscaled to Lebanon (European Monitoring and Evaluation Programme, EMEP; Atmospheric Chemistry and Climate Model Intercomparison Project, ACCMIP; and MACCity, Monitoring Atmospheric Composition and Climate and megaCITY Zoom for the Environment). The assessment was conducted through the comparison of the emission ratios (ERs) extracted from the emission inventories to the ones obtained from the hourly observations collected at a suburban site in Beirut, Lebanon, during summer and winter ECOCEM (Emissions and Chemistry of Organic Carbon in the Eastern Mediterranean) campaigns. The observed ERs were calculated using two independent methods. ER values from both methods agree very well and are comparable to the ones of the road transport sector from near-field measurements for more than 80 % of the species. There is no significant seasonality in ER for more than 90 % of the species, unlike the seasonality usually observed in other cities worldwide. Regardless of the season, ERs agree within a factor of 2 between Beirut and other representative cities worldwide, except for the unburned fuel fraction and ethane. ERs of aromatics (except benzene) are higher in Beirut compared to northern post-industrialized countries and even the Middle Eastern city Mecca. The comparison of the observed ER to the ones extracted from the ACCMIP and MACCity global emission inventories suggests that the overall speciation of anthropogenic sources for major hydrocarbons that act as ozone and secondary organic aerosol (SOA) precursors in ACCMIP is better represented than other species. The comparison of the specific road transport ERs, relative to acetylene derived from near-field measurements, to ERs from ACCMIP and EMEP emission inventories for the road transport sector showed that ERs of more reactive species are usually consistent within a factor of 2 with EMEP, while xylenes and toluene are underestimated by over a factor of 2 by ACCMIP. The observed heterogeneity of anthropogenic VOC emission composition between Middle Eastern cities can be significant for reactive VOCs but is not depicted by global emission inventories. This suggests that systematic and detailed measurements are needed in the eastern Mediterranean Basin in order to better constrain emission inventory.

Quantification of furandiones in ambient aerosol

Furandiones are products of the photooxidation of anthropogenic volatile organic compounds (VOC), like toluene, and contribute to secondary organic aerosol (SOA). Because few molecular tracers of anthropogenic SOA are used to assess this source in ambient aerosol, developing a quantification method for furandiones holds a great importance. In this study, we developed a direct and highly sensitive gas chromatography-mass spectrometry method for the quantitative analysis of furandiones in fine particulate matter that is mainly free from interference by structurally-related dicarboxylic acids. Our application of this method in Iowa City, IA provides the first ambient measurements of four furandiones: 2,5-furandione, 3-methyl-2,5-furandione, dihydro-2,5-furandione, and dihydro-3-methyl-2,5-furandione. Furandiones were detected in all collected samples with a daily average concentration of 9.1 ± 3.8 ng m−3. The developed method allows for the accurate measurement of the furandiones concentrations in ambient aerosol, which will support future evaluation of these compounds as tracers for anthropogenic SOA and assessment of their potential health impacts.

Detection and identification of Criegee intermediates from the ozonolysis of biogenic and anthropogenic VOCs: comparison between experimental measurements and theoretical calculations.

Ozonolysis of alkenes is a key reaction in the atmosphere, playing an important role in determining the oxidising capacity of the atmosphere and acting as a source of compounds that can contribute to local photochemical “smog”. The reaction products of the initial step of alkene-ozonolysis are Criegee intermediates (CIs), which have for many decades eluded direct experimental detection because of their very short lifetime. We use an innovative experimental technique, stabilisation of CIs with spin traps and analysis with proton transfer reaction mass spectrometry, to measure the gas phase concentration of a series of CIs formed from the ozonolysis of a range of both biogenic and anthropogenic alkenes in flow tube experiments. Density functional theory (DFT) calculations were used to assess the stability of the CI-spin trap adducts and show that the reaction of the investigated CIs with the spin trap occurs very rapidly except for the large β-pinene CI. Our measurement method was used successfully to measure all the expected CIs, emphasising that this new technique is applicable to a wide range of CIs with different molecular structures that were previously unidentified experimentally. In addition, for the first time it was possible to study CIs simultaneously in an even more complex reaction system consisting of more than one olefinic precursor. Comparison between our new experimental measurements, calculations of stability of the CI-spin trap adducts and results from numerical modelling, using the master chemical mechanism (MCM), shows that our new method can be used for the quantification of CIs produced in situ in laboratory experiments.

VOC emission rates over London and South East England obtained by airborne eddy covariance.

Volatile organic compounds (VOCs) originate from a variety of sources, and play an intrinsic role in influencing air quality. Some VOCs, including benzene, are carcinogens and so directly affect human health, while others, such as isoprene, are very reactive in the atmosphere and play an important role in the formation of secondary pollutants such as ozone and particles. Here we report spatially-resolved measurements of the surface-to-atmosphere fluxes of VOCs across London and SE England made in 2013 and 2014. High-frequency 3-D wind velocities and VOC volume mixing ratios (made by proton transfer reaction - mass spectrometry) were obtained from a low-flying aircraft and used to calculate fluxes using the technique of eddy covariance. A footprint model was then used to quantify the flux contribution from the ground surface at spatial resolution of 100 m, averaged to 1 km. Measured fluxes of benzene over Greater London showed positive agreement with the UK's National Atmospheric Emissions Inventory, with the highest fluxes originating from central London. Comparison of MTBE and toluene fluxes suggest that petroleum evaporation is an important emission source of toluene in central London. Outside London, increased isoprene emissions were observed over wooded areas, at rates greater than those predicted by a UK regional application of the European Monitoring and Evaluation Programme model (EMEP4UK). This work demonstrates the applicability of the airborne eddy covariance method to the determination of anthropogenic and biogenic VOC fluxes and the possibility of validating emission inventories through measurements.

亚热带竹林地区的臭氧及其影响因子

2012年7月至2013年1月，在我国浙江省亚热带竹林开展了挥发性有机物(BVOCs)排放、O3、太阳辐射、气象参数等的综合测量。基于PAR能量平衡原理和冠层尺度异戊二烯和单萜烯排放经验模式，建立了考虑O3与异戊二烯和O3与单萜烯关系的O3经验模式，该模式对于O3日变化和平均值有较好的模拟。对经验模式进行了检验，结果表明它可以较好地捕捉O3的变化特征。利用经验模式计算了O3对各个因子(异戊二烯或单萜烯、PAR、水汽、S/Q-散射因子，散射辐射/总辐射)变化的敏感性：对于O3与异戊二烯关系的O3经验模式，O3对PAR的变化最敏感，其次是水汽因子，再次是异戊二烯；最后是S/Q；对于O3与单萜烯关系的O3经验模式，O3对PAR的变化最敏感，其次是水汽和S/Q因子，最后是单萜烯；O3对各因子变化的响应均是非线性的。敏感性研究给出了与实测数据较为一致的结果，增加了我们对于O3、BVOCs化学和光化学机制的理解和认识。基于测量和敏感性研究，提出未来控制高浓度O3污染的一些建议：控制人为原因引起的BVOCs排放、人为源挥发性有机物排放、以及NOx和SO2排放等。 During July 2012-January 2013, integrated measurements of biogenic volatile organic compounds (BVOCs), O3 and solar radiation at a subtropical bamboo forest, Zhejiang province, were carried out. Based on PAR energy balance and empirical models of isoprene and monoterpene emissions at canopy scale, O3 empirical models considering the relationships between O3 and isoprene and O3 and monoterpenes, respectively, were developed. O3 diurnal variation and mean value were better simulated by O3 empirical models. The validation of O3 empirical models was made, which showed that it can capture O3 variation characteristics. A sensitivity study of the response of O3 to changes in its controlling factors (i.e., isoprene or monoterpenes, PAR, water vapor and S/Q-scat- tering factor, ratio of solar scattering radiation to solar global radiation) showed that O3 was most sensitive to PAR, and more sensitive to water vapor, isoprene emission and S/Q, for O3 empirical model considering the relationship of O3 with isoprene emission; O3 was also most sensitive to PAR, and more sensitive to water vapor, S/Q and monoterpene emissions, for O3 empirical model considering the relationship of O3 with monoterpene emissions. The responses of O3 to changes of all controlling factors were nonlinear. The sensitivity studies exhibited good agreements with the observations, and improved our understanding of chemical and photochemical mechanisms associated with O3 and BVOCs. Some suggestions in controlling future high O3 pollution were put forwarded, e.g., controlling emissions of Human-induced BVOC emissions, anthropogenic volatile organic compound emissions, and NOx and SO2 emissions.

Atmospheric Emission Characteristics and Control Policies of Anthropogenic VOCs from Industrial Sources in Yangtze River Delta Region, China

ABSTRACTA bottom-up inventory of atmospheric emissions of industrial MNVOCs in Yangtze River Delta (YRD) region was established for the period of 2010–2012. Results indicated that the total emissions of industrial VOCs increased from 3.34 Tg in 2010 to 3.99 Tg in 2012 at an annual average rate of 9.3%. Furniture manufacturing, machinery equipment manufacturing, architectural ornament, and petroleum refining were estimated to be the key sources, which contributed 58.6% of the total emissions in 2012. Based on the population database, the emission inventory was gridded into 1 km × 1 km grid cells with ArcGIS, which indicated that VOC emissions exhibited remarkable spatial and temporal characteristics. The most polluted areas were mainly centered in Shanghai, Nanjing, Ningbo, Hefei, and the Hangzhou and Taihu lake basin, which were the most developed and industrialized regions in the YRD. VOC emissions from specified anthropogenic sources under three different control scenarios for the different emission targets in 2030 were projected. The estimated average removal efficiency of the control technologies for each anthropogenic source should improve by 68.1% (scenario 2030B) and 79.0% (scenario 2030C). An entire process-control management scheme needs to be established based on the investigation of industrial processes, and the proportion of the application should be improved in the future.

Atmospheric Chemistry of α‐Diketones: Kinetics of C5 and C6 Compounds with Cl Atoms and OH Radicals

ABSTRACTCarbonyls play an important role in atmospheric chemistry due to their formation in the photooxidation of biogenic and anthropogenic volatile organic compounds and their high atmospheric reactivity. The Cl‐initiated kinetics of two α‐diketones (2,3‐pentanedione (PTD) and 2,3‐hexanedione (HEX)) have been determined as well as the OH + HEX rate constant using atmospheric simulation chamber experiments and the relative rate method. Up to three different reference compounds were used to assess robust results. The following rate constants (in cm3 molecule−1 s−1) have been obtained at 298 K: k(Cl + PTD) = (1.6 ± 0.2) × 10−11, k(Cl + HEX) = (8.8 ± 0.4) × 10−11, and k(OH + HEX) = (3.6 ± 0.7) × 10−12 with a global uncertainty of 30%. The present determinations of Cl‐ and OH‐ reaction rate constants for HEX constitute first measurements. Using the present measurements, a recently improved structure–activity relationship for Cl + ketone reactions has been updated by introducing an F(–COCO–) factor of 8.33 × 10−4. Atmospheric lifetime calculations indicate that chlorine‐initiated oxidation may be a significant α‐diketone sink in the marine‐boundary layer or in places where high Cl concentrations may be found.

Emission Inventory of Anthropogenic VOCs and Its Contribution to Ozone Formation in Shanxi Province

Based on the activity levels, emission factors and composition characteristics of VOCs, which was obtained in statistic data and references, the emission amount of anthropogenic VOCs in Shanxi province in 2013 was calculated, and the ozone formation potential of VOCs was studied in this study. The results showed that the emission amount of anthropogenic VOCs in Shanxi province in 2013 was 723700 t, with the major sector of the industrial emission and vehicle emission, accounting for 36.47% and 24.28% of total emission amount, respectively. Coke and chemicals production, the major emission source of VOCs in industrial emission, emitting 190600 t and 38800 t VOCs in 2013, accounting for 72.22% and 14.72% of industrial emission, respectively. The emission amount of ozone precursor VOCs was 435900 t, and the total amount of ozone formation potential in Shanxi province in 2013 was 1769900 t. The sources of the greatest contribution to total ozone were vehicle emission, combustion sources and industrial emission. The results indicated that industrial emission was the major source of VOCs emission, which showed the simplification and heavy industrial structure. The increasing numbers of vehicles led to the huge emission of VOCs in recent years. In conclusion, the main measure of controlling the ozone pollution caused by VOCs emissions was controlling the VOCs emission from industrial emission and vehicle emission.

Contributions and source identification of biogenic and anthropogenic hydrocarbons to secondary organic aerosols at Mt. Tai in 2014

Ambient fine particulate matter (PM2.5) and volatile organic compounds (VOCs) collected at Mt. Tai in summer 2014 were analysed and the data were used to identify the contribution of biogenic and anthropogenic hydrocarbons to secondary organic aerosols (SOA) and their sources and potential source areas in high mountain regions. Compared with those in 2006, the 2014 anthropogenic SOA tracers in PM2.5 aerosols and VOC species related to vehicular emissions exhibited higher concentrations, whereas the levels of biogenic SOA tracers were lower, possibly due to decreased biomass burning. Using the SOA tracer and parameterisation method, we estimated the contributions from biogenic and anthropogenic VOCs, respectively. The results showed that the average concentration of biogenic SOA was 1.08 ± 0.51 μg m−3, among which isoprene SOA tracers were dominant. The anthropogenic VOC-derived SOA were 7.03 ± 1.21 μg m−3 and 1.92 ± 1.34 μg m−3 under low- and high-NOx conditions, respectively, and aromatics made the greatest contribution. However, the sum of biogenic and anthropogenic SOA only contributed 18.1–49.1% of the total SOA. Source apportionment by positive matrix factorisation (PMF) revealed that secondary oxidation and biomass burning were the major sources of biogenic SOA tracers. Anthropogenic aromatics mainly came from solvent use, fuel and plastics combustion and vehicular emissions. However, for > C6 alkanes and cycloalkanes, vehicular emissions and fuel and plastics combustion were the most important contributors. The potential source contribution function (PSCF) identified the Bohai Sea Region (BSR) as the major source area for organic aerosol compounds and VOC species at Mt. Tai.

Ozone air quality simulations with WRF-Chem (v3.5.1) over Europe: model evaluation and chemical mechanism comparison

Abstract. We present an evaluation of the online regional model WRF-Chem over Europe with a focus on ground-level ozone (O3) and nitrogen oxides (NOx). The model performance is evaluated for two chemical mechanisms, MOZART-4 and RADM2, for year-long simulations. Model-predicted surface meteorological variables (e.g., temperature, wind speed and direction) compared well overall with surface-based observations, consistent with other WRF studies. WRF-Chem simulations employing MOZART-4 as well as RADM2 chemistry were found to reproduce the observed spatial variability in surface ozone over Europe. However, the absolute O3 concentrations predicted by the two chemical mechanisms were found to be quite different, with MOZART-4 predicting O3 concentrations up to 20 µg m−3 greater than RADM2 in summer. Compared to observations, MOZART-4 chemistry overpredicted O3 concentrations for most of Europe in the summer and fall, with a summertime domain-wide mean bias of +10 µg m−3 against observations from the AirBase network. In contrast, RADM2 chemistry generally led to an underestimation of O3 over the European domain in all seasons. We found that the use of the MOZART-4 mechanism, evaluated here for the first time for a European domain, led to lower absolute biases than RADM2 when compared to ground-based observations. The two mechanisms show relatively similar behavior for NOx, with both MOZART-4 and RADM2 resulting in a slight underestimation of NOx compared to surface observations. Further investigation of the differences between the two mechanisms revealed that the net midday photochemical production rate of O3 in summer is higher for MOZART-4 than for RADM2 for most of the domain. The largest differences in O3 production can be seen over Germany, where net O3 production in MOZART-4 is seen to be higher than in RADM2 by 1.8 ppb h−1 (3.6 µg m−3 h−1) or more. We also show that while the two mechanisms exhibit similar NOx sensitivity, RADM2 is approximately twice as sensitive to increases in anthropogenic VOC emissions as MOZART-4. Additionally, we found that differences in reaction rate coefficients for inorganic gas-phase chemistry in MOZART-4 vs. RADM2 accounted for a difference of 8 µg m−3, or 40 % of the summertime difference in O3 predicted by the two mechanisms. Differences in deposition and photolysis schemes explained smaller differences in O3. Our results highlight the strong dependence of modeled surface O3 over Europe on the choice of gas-phase chemical mechanism, which we discuss in the context of overall uncertainties in prediction of ground-level O3 and its associated health impacts (via the health-related metrics MDA8 and SOMO35).

Changing odour landscapes: the effect of anthropogenic volatile pollutants on plant–pollinator olfactory communication

Summary Olfactory signals, often in synergy with visual signals, mediate the interactions between plants and animals. However, urbanization and agricultural practices are both sources of volatile organic compounds (VOCs) and reactive oxygen species (ROS) that have the potential to interfere with plant–animal communication and to disrupt mutualistic interactions. In this review, we explore how anthropogenic airborne pollutants may disrupt chemical information transfer between flowering plants and flower visitors. The emission of anthropogenic volatile pollutants (AVPs) including VOCs and formation of ROS, for example from traffic or industries, and non‐natural biogenic VOCs, for example from introduced crops, may have a number of effects: (i) changes in plant signalling as a consequence of plants experiencing physiological stress; (ii) chemical interference (chemical degradation/transformation of infochemicals); (iii) increased levels of background noise impeding signal detection; and (iv) changes in pollinator signal perception and behaviour. All of the above in turn could have consequences for the biological fitness of plants and animals that rely on olfactory information as pivotal functional signals. The study of anthropogenic airborne pollutants and their effects on plant signalling is just emerging and the impacts of this aspect of anthropogenic emissions are barely understood. Volatiles emitted from anthropogenically changed landscapes could, however, have far‐reaching consequences for ecosystem functioning in adjacent natural zones, particularly in fragmented landscapes. In response to the wide gap in our knowledge on the mechanisms that govern interference of anthropogenic VOCs with olfactory information, future research directions are proposed with the aim to inspire research to help elucidate the risks of anthropogenic VOCs for plant–pollinator communities and improve risk assessment strategies. A lay summary is available for this article.

Urban forests near roads do not reduce gaseous air pollutant concentrations but have an impact on particles levels

The ability of urban vegetation to improve air quality for the benefit of urban residents is often considered fact since plants can absorb and capture air pollutants. However, there is little empirical evidence that urban air quality at the local scale is improved by the presence of, e.g. trees, especially in northern climatic regions. We studied the impact of urban forest vegetation on the levels of five types of air pollutants (NO2, ground-level O3, anthropogenic and biogenic VOCs, and particulate matter) in near-road environments during summer (June) using passive samplers in Helsinki, Finland. Concentrations of gaseous pollutants did not differ significantly between tree-covered and adjacent open areas, while particle pollutant levels were significantly lower in tree-covered areas than in adjacent open, treeless areas. Vegetation-related variables (canopy closure, tree number and size, and ground vegetation) did not explain differences in air quality. Our results suggest that the role of urban, mostly deciduous, vegetation is negligible in improving local air quality, in terms of the anthropogenic pollutants measured here, in northern climates. However, air particulate pollution, which is likely to be dominated by large-sized particles in our study, can be reduced by urban vegetation.

Ozone sensitivity to isoprene chemistry and emissions and anthropogenic emissions in central California

Ozone formation in California in year 2017 was simulated using three chemical mechanisms: the Statewide Air Pollution Research Center 2007 mechanism with updated toxics and isoprene chemistry (S07TIC); the Carbon Bond 6, revision 2 (CB6r2) mechanism; a modified CB6r2 mechanism with increased hydroxyl radical (OH) production from isoprene oxidation at low nitrogen oxide (NOx) concentrations (CB6r2OH). The simulations with a photochemical grid model (PGM) showed little difference in ozone between CB6r2 and CB6r2OH. Further analysis with a box model found little sensitivity of ozone to OH production in the isoprene chemistry of all three mechanisms under conditions representative of California. The S07TIC generally predicts greater ozone than the CB6r2, and the difference in the predicted concentrations exceeds the uncertainty estimated from uncertainties in the emissions inventory. The sensitivity of ozone to anthropogenic volatile organic compound (VOC), NOx and carbon monoxide (CO) emissions and to isoprene emissions was also calculated with the PGM. Accounting for uncertainties in the emissions inventory, the sensitivity to NOx emissions is significantly different between S07TIC and CB6r2 in central and northern California; the sensitivity to isoprene emissions is significantly different in southern California. All mechanisms give a negative sensitivity of ozone to isoprene emissions in areas of northern California where NOx emissions are small. The CB6r2 and S07TIC differ in the sensitivity of ozone to organic nitrate (ON) formation from isoprene oxidation, likely because all ONs recycle to NOx in the S07TIC mechanism but only first-generation ONs do so in the CB6r2. For current California conditions, uncertainties in OH production from isoprene have little impact on ozone, but the extent to which isoprene ONs recycle NOx does impact ozone concentration and ozone sensitivity to NOx emissions.

Seasonal variations of fine particulate organosulfates derived from biogenic and anthropogenic hydrocarbons in the mid-Atlantic United States

Organosulfates (OSs) are an important and ubiquitous class of organic compounds found in ambient fine particulate matter (PM2.5) that serves as markers for multiphase chemical processes leading to secondary organic aerosol (SOA) formation. In this study, high-volume filter sampling was implemented to collect PM2.5 samples during the August 2012–June 2013 time period in suburban Towson, MD. By utilizing ultra-performance liquid chromatography coupled with high-resolution quadrupole time-of-flight mass spectrometry employing an electrospray ionization source (UPLC/ESI-HR-QTOFMS), 58 OSs were characterized and quantified in PM2.5 collected across all seasons. The selection of the extraction solvent was also found to be important for OS characterization. Seasonal trends demonstrate that the atmospheric oxidation of biogenic volatile organic compounds (VOCs) dominates OS formation in early fall and spring, with substantial contributions from isoprene OS (∼15 ng/m3), and limonene and α-pinene OS (∼5 ng/m3). From November to March anthropogenic OSs, including polycyclic aromatic hydrocarbon (PAH)- and alkane-derived OSs recently characterized in laboratory-generated SOA, reached their highest levels averaging 4 ng/m3. Nitrogen-containing OSs derived from terpene chemistry remain consistent over the sampling period averaging 2 ng/m3 and do not demonstrate strong seasonal fluctuations. Correlations between the identified OSs and known organic acids that arise from either the atmospheric oxidation of biogenic or anthropogenic VOCs assist in source apportionment. Meteorological data coupled with air mass back-trajectory analyses using HYSPLIT provide insight into meteorological and transport conditions that promote the formation/occurrence of OSs within the mid-Atlantic U.S. region.

Impacts of projected changes of emissions and climate on future U.S. Air quality

Projected changes in emissions and climate will impact future air quality and related human and environmental health. In this work, an advanced online-coupled meteorology and chemistry model, the Weather Research and Forecasting Model with Chemistry (WRF/Chem), has been applied to the continental U.S. for current (2001–2010) and future (2046–2055) decades under four emission/ climate scenarios including the Representative Concentration Pathways (RCP) 4.5 and 8.5 that regulate future radiative forcing and the Technology-driven model (TDM) A1B and B2 that explicitly simulate the relationship between the socioeconomic variables and technological changes. A comprehensive evaluation has been performed for current decade using available observations from surface networks and satellites and shows an overall good performance in reproducing observations. The future decadal simulations show that future climate features with stronger radiation, higher surface temperature and planetary boundary layer height, and enhanced precipitation under all scenarios, with less warming and drier atmosphere by RCP4.5 than 8.5 and by TDM B2 than A1B. The simulations under RCP8.5/TDM A1B show the enhanced future O 3 levels, which are attributed to warmer climate, higher emissions of methane (CH 4 ) and biogenic volatile organic compounds (VOCs), and dis-benefit of nitrogen oxides (NO x ) reduction in VOC-limited regime. The latter factor offsets the benefits of reduced emissions of NO x and anthropogenic VOCs. Future air quality features greater reduction in PM 2.5 by RCP4.5/8.5 than TDM B2/A1B and decreased O 3 over most areas by RCP4.5 and TDM B2, indicating the benefits of carbon policy and technology changes with greater emission reductions and the importance of win–win emission control strategies in mitigating air pollution and adverse climate change.

Relative humidity-dependent viscosity of secondary organic material from toluene photo-oxidation and possible implications for organic particulate matter over megacities

Abstract. To improve predictions of air quality, visibility, and climate change, knowledge of the viscosities and diffusion rates within organic particulate matter consisting of secondary organic material (SOM) is required. Most qualitative and quantitative measurements of viscosity and diffusion rates within organic particulate matter have focused on SOM particles generated from biogenic volatile organic compounds (VOCs) such as α-pinene and isoprene. In this study, we quantify the relative humidity (RH)-dependent viscosities at 295 ± 1 K of SOM produced by photo-oxidation of toluene, an anthropogenic VOC. The viscosities of toluene-derived SOM were 2 × 10−1 to ∼ 6 × 106 Pa s from 30 to 90 % RH, and greater than ∼ 2 × 108 Pa s (similar to or greater than the viscosity of tar pitch) for RH ≤ 17 %. These viscosities correspond to Stokes–Einstein-equivalent diffusion coefficients for large organic molecules of ∼ 2 × 10−15 cm2 s−1 for 30 % RH, and lower than ∼ 3 × 10−17 cm2 s−1 for RH ≤ 17 %. Based on these estimated diffusion coefficients, the mixing time of large organic molecules within 200 nm toluene-derived SOM particles is 0.1–5 h for 30 % RH, and higher than ∼ 100 h for RH ≤ 17 %. As a starting point for understanding the mixing times of large organic molecules in organic particulate matter over cities, we applied the mixing times determined for toluene-derived SOM particles to the world's top 15 most populous megacities. If the organic particulate matter in these megacities is similar to the toluene-derived SOM in this study, in Istanbul, Tokyo, Shanghai, and São Paulo, mixing times in organic particulate matter during certain periods of the year may be very short, and the particles may be well-mixed. On the other hand, the mixing times of large organic molecules in organic particulate matter in Beijing, Mexico City, Cairo, and Karachi may be long and the particles may not be well-mixed in the afternoon (15:00–17:00 LT) during certain times of the year.

Ozone and secondary organic aerosol formation potential from anthropogenic volatile organic compounds emissions in China

Volatile organic compounds (VOCs) are major precursors for ozone and secondary organic aerosol (SOA), both of which greatly harm human health and significantly affect the Earth's climate. We simultaneously estimated ozone and SOA formation from anthropogenic VOCs emissions in China by employing photochemical ozone creation potential (POCP) values and SOA yields. We gave special attention to large molecular species and adopted the SOA yield curves from latest smog chamber experiments. The estimation shows that alkylbenzenes are greatest contributors to both ozone and SOA formation (36.0% and 51.6%, respectively), while toluene and xylenes are largest contributing individual VOCs. Industry solvent use, industry process and domestic combustion are three sectors with the largest contributions to both ozone (24.7%, 23.0% and 17.8%, respectively) and SOA (22.9%, 34.6% and 19.6%, respectively) formation. In terms of the formation potential per unit VOCs emission, ozone is sensitive to open biomass burning, transportation, and domestic solvent use, and SOA is sensitive to industry process, domestic solvent use, and domestic combustion. Biomass stoves, paint application in industrial protection and buildings, adhesives application are key individual sources to ozone and SOA formation, whether measured by total contribution or contribution per unit VOCs emission. The results imply that current VOCs control policies should be extended to cover most important industrial sources, and the control measures for biomass stoves should be tightened. Finally, discrepant VOCs control policies should be implemented in different regions based on their ozone/aerosol concentration levels and dominant emission sources for ozone and SOA formation potential.

Organic nitrate chemistry and its implications for nitrogen budgets in an isoprene- and monoterpene-rich atmosphere: constraints from aircraft (SEAC4RS) and ground-based (SOAS) observations in the Southeast US.

Formation of organic nitrates (RONO2) during oxidation of biogenic volatile organic compounds (BVOCs: isoprene, monoterpenes) is a significant loss pathway for atmospheric nitrogen oxide radicals (NOx), but the chemistry of RONO2 formation and degradation remains uncertain. Here we implement a new BVOC oxidation mechanism (including updated isoprene chemistry, new monoterpene chemistry, and particle uptake of RONO2) in the GEOS-Chem global chemical transport model with ∼25 × 25 km2 resolution over North America. We evaluate the model using aircraft (SEAC4RS) and ground-based (SOAS) observations of NOx, BVOCs, and RONO2 from the Southeast US in summer 2013. The updated simulation successfully reproduces the concentrations of individual gas- and particle-phase RONO2 species measured during the campaigns. Gas-phase isoprene nitrates account for 25-50% of observed RONO2 in surface air, and we find that another 10% is contributed by gas-phase monoterpene nitrates. Observations in the free troposphere show an important contribution from long-lived nitrates derived from anthropogenic VOCs. During both campaigns, at least 10% of observed boundary layer RONO2 were in the particle phase. We find that aerosol uptake followed by hydrolysis to HNO3 accounts for 60% of simulated gas-phase RONO2 loss in the boundary layer. Other losses are 20% by photolysis to recycle NOx and 15% by dry deposition. RONO2 production accounts for 20% of the net regional NOx sink in the Southeast US in summer, limited by the spatial segregation between BVOC and NOx emissions. This segregation implies that RONO2 production will remain a minor sink for NOx in the Southeast US in the future even as NOx emissions continue to decline.

Urban stress-induced biogenic VOC emissions and SOA-forming potentials in Beijing

Abstract. Trees can significantly impact the urban air chemistry by the uptake and emission of reactive biogenic volatile organic compounds (BVOCs), which are involved in ozone and particle formation. Here we present the emission potentials of "constitutive" (cBVOCs) and "stress-induced" BVOCs (sBVOCs) from the dominant broadleaf woody plant species in the megacity of Beijing. Based on the municipal tree census and cuvette BVOC measurements on leaf level, we built an inventory of BVOC emissions, and assessed the potential impact of BVOCs on secondary organic aerosol (SOA) formation in 2005 and 2010, i.e., before and after realizing the large tree-planting program for the 2008 Olympic Games. We found that sBVOCs, such as fatty acid derivatives, benzenoids, and sesquiterpenes, constituted a significant fraction ( ∼ 40 %) of the total annual BVOC emissions, and we estimated that the overall annual BVOC budget may have doubled from ∼ 4.8 × 109 g C year−1 in 2005 to ∼ 10.3 × 109 g C year−1 in 2010 due to the increase in urban greening, while at the same time the emission of anthropogenic VOCs (AVOCs) decreased by 24 %. Based on the BVOC emission assessment, we estimated the biological impact on SOA mass formation potential in Beijing. Constitutive and stress-induced BVOCs might produce similar amounts of secondary aerosol in Beijing. However, the main contributors of SOA-mass formations originated from anthropogenic sources (> 90 %). This study demonstrates the general importance to include sBVOCs when studying BVOC emissions. Although the main problems regarding air quality in Beijing still originate from anthropogenic activities, the present survey suggests that in urban plantation programs, the selection of low-emitting plant species has some potential beneficial effects on urban air quality.