Control Of Volatile Organic Compounds Research Articles

Development of seasonal ozone maximum reactivity scales for Beijing, China

We designed scenarios based on urban emissions to develop a Maximum Incremental Reactivity (MIR) scale for 41 conventional volatile organic compounds (VOCs) in Beijing and quantitatively analyzed the various factors affecting MIR in urban areas. We explored the effects of updating the representative urban atmosphere used for ozone reactivity calculations by incorporating updated meteorological data, emission rates, initial condition concentrations, and VOC profile compositions. A box model equipped with the Master Chemical Mechanism (MCM) was used to localize the MIR scale for Beijing based on urban emission model inputs, and this was compared with scenarios in the United States. The MIR differences for most VOC species were minimal; however, Beijing exhibited higher MIR values for aromatic hydrocarbons in the summer, attributed to the higher emission intensity of aromatics in the city. Due to differences in meteorological conditions and emission scenarios, the MIR showed significant seasonal characteristics across different months. It is necessary to calculate independent MIR scales for different urban agglomerations under specific ozone pollution seasons and emission conditions. This study provides recommendations for the application of the MIR scale and can serve as a reference for VOC control strategies in China and other countries facing ozone pollution.

Spatial-Temporal Characteristics, Source Apportionment, and Health Risks of Atmospheric Volatile Organic Compounds in China: A Comprehensive Review.

Volatile organic compounds (VOCs) are ubiquitous in the atmosphere, posing significant adverse impacts on air quality and human health. However, current research on atmospheric VOCs mainly focuses on specific regions or industries, without comprehensive national-level analysis. In this study, a total of 99 articles on atmospheric VOCs in China published from 2015 to 2024 were screened, and data on their concentrations, source apportionment, and health risks were extracted and summarized. The results revealed that the annual average concentrations of TVOCs and their groups in China generally increased and then decreased between 2011 and 2022, peaking in 2018-2019. A distinct seasonal pattern was observed, with the highest concentrations occurring in winter, followed by autumn, spring, and summer. TVOC emissions were highly concentrated in northern and eastern China, mainly contributed by alkanes and alkenes. Source apportionment of VOCs indicated that vehicle sources (32.9% ± 14.3%), industrial emissions (18.0% ± 12.8%), and other combustion sources (13.0% ± 13.0%) were the primary sources of VOCs in China. There was a significant positive correlation (p < 0.05) between the annual mean VOC concentration and population size, and a notable negative correlation (p < 0.05) with GDP per capita. Atmospheric VOCs had no non-carcinogenic risk (HI = 0.5) but exhibited a probable carcinogenic risk (7.5 × 10-5), with relatively high values for 1,2-dibromoethane, 1,2-dichloroethane, and naphthalene. The health risk was predominantly driven by halocarbons. These findings are essential for a better understanding of atmospheric VOCs and for developing more targeted VOC control measures.

The source of volatile organic compounds pollution and its effect on ozone in high-altitude areas

Volatile organic compounds (VOCs) are crucial precursors in the formation of ozone (O3). The sources of pollution are complex and significantly impact O3 generation. Long-term exposure to high-concentration O3 environments causes serious damage to organisms. High-altitude areas experience continuous high temperatures and strong solar radiation, which can easily produce O3 through photochemical reactions, making these areas prone to frequent air pollution. This study utilizes the National Positioning Station of the Yinchuan Urban Ecosystem in Ningxia to conduct field synchronous observations, gathering data on VOCs, meteorological variables, and O3. By employing machine learning algorithms, we examined the seasonal distribution characteristics of VOCs, their pollution sources, and their impact on O3. The results show that the seasonal distribution of VOCs areas is low in spring and autumn and high in summer and winter. The components with higher volume fraction contribution are m-tolualdehyde in spring and summer, ethane in autumn, and acetylene in winter. The main emission sources of VOCs pollution are hydrocarbon volatile emission in spring and winter, solvent volatilization emission in summer, and industrial sources in autumn. VOCs have a negative effect on O3, with a greater impact in winter and spring, evidenced by standardized effect values of −0.26 and −0.24. The key components affecting O3 in VOCs vary by season. Aromatic hydrocarbons are the key components in spring and winter, with contribution rates of 22 % and 21.3 %. Alkenes are the key components in summer and autumn (24.5 % and 26.8 %). Among meteorological variables, temperature is the key factor affecting O3, while wind speed is the key factor affecting O3 only in winter. This study aims to clarify the sources of VOCs pollution in different seasons and their impact on O3, providing a theoretical basis and technical support for the prevention and control of VOCs and O3 pollution in high-altitude areas.

Source apportionment of Volatile Organic Compounds (VOCs) in the South Coast Air Basin (SoCAB) During RECAP-CA

Ozone (O3) concentrations in the South Coast Air Basin (SoCAB) surrounding Los Angeles remain at unhealthy levels despite multiple decades of control programs designed to reduce emissions of precursor Volatile Organic Compounds (VOCs). Here we report on comprehensive VOC measurements made at Redlands, which has the highest measured O3 concentrations in SoCAB, as part of the Re-Evaluating the Chemistry of Air Pollutants in California (RECAP-CA) field campaign (July–October 2021). Positive matrix factorization (PMF) analysis was applied to identify nine VOC factors. A photochemical chamber model initialized by field measurements was configured with a tagging technique to quantify the VOC factor contributions to O3 formation in Redlands. Biogenic VOCs (BVOCs) made the largest contribution (26.6%) to O3 formation, followed by traffic VOCs (21.2%), volatile chemical products (VCPs) (19%), and plant decomposition (14.9%). High O3 episodes were not driven by increased VOC emissions from any single source, but rather were associated with stagnation events that concentrated VOCs from all sources and high temperature days that enhanced O3 formation efficiency. This implies that VOC controls optimized to reduce O3 concentrations would look similar in both the NOx-limited and VOC-limited regimes that can occur at Redlands. These results suggest that control strategies that reduce VOC and NOx emissions from the on-road vehicle fleet, such as increasing electrification, may yield O3 reductions on days in both the NOx-limited and VOC-limited chemical regimes at Redlands.

Pollution Characterization and Source Apportionment of Volatile Organic Compounds and Their Odor-causing Species in Industrial Parks

To improve the phenomenon of the volatile organic compounds （VOCs） odor pollution nuisance in industrial parks and to promote the synergistic control of atmospheric VOCs and their odor-causing substances, based on the field observation of atmospheric VOCs in residential living areas and five different types of industrial clusters in industrial parks, we analyzed the pollution characteristics of atmospheric VOCs and their odor-causing volatile organic compounds （O-VOCs） in the residential living areas and each industrial cluster, evaluated the characteristics of the odor activity of the O-VOCs in the industrial parks, and identified the key odor-causing species and their main sources. The results showed that the mean values of atmospheric φ （TVOCs） and φ（O-VOCs） in the residential living area of the industrial park were 102.57×10-9 and 72.33×10-9, respectively. φ（TVOCs） and φ（O-VOCs） were significantly higher in the industrial clusters of basic chemical industry and pharmaceutics than in the other industrial clusters, and the sum （OAVsum） and maximum （OAVmax） of the odor activity values of these two clusters were relatively high, with a potential risk of odor nuisance. Overall, the O-VOCs species with higher odor intensity were similar in residential living areas and the five industrial clusters, and effective control of O-VOCs species such as acrolein, p-diethylbenzene, p-xylene, and 1,3-diethylbenzene is essential to mitigate or eliminate organic odor pollution. The results of the source apportionment of O-VOCs in the residential area showed that the sources of O-VOCs in the residential area were mainly influenced by natural gas chemical and pharmaceutics, and the coefficients of divergence （CDO-VOCs） between the O-VOC chemical profiles from residential areas and those from natural gas chemical and pharmaceutics were 0.31 and 0.38, respectively. Principal component analysis （PCA） also confirmed this result, with residential O-VOCs mainly originating from natural gas chemicals and pharmaceutics, followed by iron and steel manufacturing and automobile manufacturing, with the lowest contribution from the basic chemicals.

Mn/CeO2 contains enriched surface lewis acid sites and pore structures accelerated catalytic oxidation of propane at low temperature

The development of highly efficient non-precious metal catalysts for the low-temperature catalytic oxidation of volatile organic compounds (VOCs) is a critical imperative in VOCs control. In this study, a series of highly active CeMnOx catalysts with Mn-doped CeO2 were investigated. The catalysts (WHSV=30,000 mL g−1 h−1) exhibited the highest catalytic propane oxidation activity (T90 = 230 °C) and excellent stability over 600 h, When the Mn:Ce ratio was 2.5. The introduction of Mn doping resulted in modifications to the pore structure of CeO2, leading to an increase in specific surface area and enhanced gas transfer kinetics. Additionally, it induced surface electronic defects and elevated the concentration of acidic sites, thereby facilitating the adsorption and activation of propane. Consequently, these improvements contributed to an enhanced catalytic performance of the catalyst. The in-situ DRIFTS infrared spectra revealed that Mn doping reduced the activation energy of the reaction and facilitated the conversion of acetone groups as well as decomposition of carboxylic acid groups.

Environmental and economic impact analysis of levying VOCs environmental protection tax in China

China is one of the largest volatile organic compounds (VOCs) emitters worldwide. The emission levels of and harm caused by VOCs have attracted much attention. China has implemented multiple policies for VOCs prevention and control but lacks economic control measures for VOCs In this study, the input-output (IO) price model was used to simulate and analyze the emission reduction and economic effects resulting from the imposition of a VOCs environmental protection tax (EPT) in 31 provinces in China. The results show that, first, the collection of a VOCs-EPT can achieve not only VOCs emission reductions but also the synergistic emission reductions of other major pollutants. Second, the collection of a VOCs-EPT could have a negative impact on the macroeconomy, i.e., the greater the tax scope and the higher the tax rate are, the greater the negative economic impact. Third, differences in the level of economic development, the structure of pollution emissions and the stringency of tax policies among regions would cause the emission reduction effect and related negative economic impact to vary across regions. Finally, the collection of a VOCs-EPT could have heterogeneous impacts on various industries, as high-emission industries would suffer greater negative impacts. Therefore, each region should set tax rates that match its provincial economic and environmental development levels. Furthermore, a VOCs-EPT can be levied on key industries, and reasonable preferential tax policies can be formulated to reduce negative macroeconomic benefits.

Fundamental insights and recent advances in catalytic oxidation processes using ozone for the control of volatile organic compounds.

The development of technologies for highly efficient treatment of emissions containing low concentrations of volatile organic compounds (VOCs) remains an important challenge. Catalytic oxidation with ozone (catalytic ozonation) is useful for the oxidative decomposition of VOCs, particularly aromatic compounds, under ambient temperature conditions. Only inexpensive transition metal oxides are required as catalysts, and Mn-based catalysts are widely used for catalytic ozonation. This review describes the oxidation reaction mechanisms, reaction pathways of aromatic hydrocarbons, and dependence of the catalytic ozonation activity on the reaction conditions. The reasons why Mn oxides are effective in catalytic ozonation are also explained. The structure of the catalytic active sites and the types of supporting materials contributing to the reaction are also discussed in detail, with the aim of establishing a VOC control technology. In addition, recent progress in catalytic oxidation processes using ozone as an oxidant has been outlined, focusing on catalyst materials and reaction conditions.

Response of ozone to meteorology and atmospheric oxidation capacity in the Yangtze river Delta from 2017 to 2020

China implemented a stringent clean air initiative to improve air quality in 2013. By 2017, fine particulate matter (PM2.5) levels in the Yangtze River Delta (YRD) region dropped significantly, but ozone (O3) pollution surged, which aroused concerns about its adverse impact on crops, climate and human health. Due to the complex influences of atmospheric processes, the variation of O3 is highly nonlinear, making the control of O3 pollution highly challenging. It is urgent to deepen the understanding of the role of meteorological factors and atmospheric oxidation capacity (AOC) during O3 episodes. To provide references for O3 pollution control, the study used the Weather Research and Forecasting model (WRF) and the Community Multi-scale Air Quality model (CMAQ) simulations in the YRD from 2017 to 2020 to analyze the causes of severe O3 pollution. Observations revealed a slight decline in heavily O3 polluted days in the YRD region and the simulation results showed that O3 pollution was more prevalent at temperatures above 25 °C and relative humidity below 80%. The increase in volatile organic compounds (VOCs), hydroxyl radical (OH) and nitrate radical (NO3) was also more conducive to the formation of O3 pollution. For areas that are primarily VOC-limited areas, such as Shanghai, a stricter policy on VOC control is needed to reduce O3 pollution more effectively.

A Year-Long Measurement and Source Contributions of Volatile Organic Compounds in Nanning, South China

Severe ozone (O3) pollution has been recorded in China in recent years. The key precursor, volatile organic compounds (VOCs), is still not well understood in Nanning, which is a less developed city compared to other megacities in China. In this study, a year-long measurement of VOCs was conducted from 1 October 2020 to 30 September 2021, to characterize the ambient variations and apportion the source contributions of VOCs. The daily-averaged concentration of VOCs was measured to be 26.4 ppb, ranging from 3.2 ppb to 136.2 ppb across the whole year. Alkanes and oxygenated VOCs (OVOCs) were major species, contributing 46.9% and 25.2% of total VOC concentrations, respectively. Propane, ethane, and ethanol were the most abundant in Nanning, which differed from the other significant species, such as toluene (3.7 ppb) in Guangzhou, ethylene (3.8 ppb) in Nanjing, and isopentane (5.5 ppb), in Chengdu. The positive matrix factorization (PMF) model resolved six source factors, including vehicular emission (contributing 33% of total VOCs), NG and LPG combustion (19%), fuel burning (17%), solvent use (16%), industry emission (10%), and biogenic emission (5%). This indicated that Nanning was less affected by industrial emission compared with other megacities of China, with industry contributing 12–50%. Ethylene, m/p-xylene, butane, propylene, and isoprene were key species determined by ozone formation potential (OFP) analysis, which should be priority-controlled. The variations in estimated OFP and observed O3 concentrations were significantly different, suggesting that VOC reactivity-based strategies as well as meteorological and NOx effects should be considered collectively in controlling O3 pollution. This study presents a year-long dataset of VOC measurements in Nanning, which gives valuable implications for VOC control in terms of key sources and reactive species and is also beneficial to the formulation of effective ozone control strategies in other less developed regions of China.

Optimization Design of a Recovery System for an Automatic Spray Robot and the Simulation of VOC Recovery

A recovery system for an automatic spraying robot to conduct the spraying operation outdoors for ships is designed in this paper, which addresses the pollution problem of volatile organic compounds (VOCs) by employing the vacuum recovery method. The recovery system consists of the recovery hood, nozzle, and vacuum tubes. The recovery hood is the critical part of the recovery system and is designed with internal and external cavities, as well as four vacuum tubes for recycling VOCs. Based on the computational fluid dynamics (CFD) method, simulation in the time domain of the gas–liquid interaction, droplet evaporation, and wall impingement is conducted. To identify the better recovery performance, three vacuum recovery-hood schemes are designed, and their performance is compared. The numerical results show that the distance between the vacuum tubes and the intake gap has a significant impact on the VOCs’ recovery effect. One of the main reasons for the escape of VOCs is that the swirling airflows in the baffle plane act as vortices which may capture VOCs, causing the accumulation of VOCs beyond the capacity of the external cavity. Dividing the external cavity into four chambers with deflectors (with each chamber equipped with one vacuum tube only) can significantly reduce the leakage rate of the recovery system. The recovery system provides a theoretical solution for implementing the prevention and control of VOCs in shipyards as soon as possible.

Enhanced VOC emission with increased temperature contributes to the shift of O3-precursors relationship and optimal control strategy

Assessing the impact of anthropogenic volatile organic compounds (VOCs) on ozone (O3) formation is vital for the management of emission reduction and pollution control. Continuous measurement of O3 and the major precursors was conducted in a typical light industrial city in the YRD region from 1 May to 25 July in 2021. Alkanes were the most abundant VOC group, contributing to 55.0% of TVOCs concentration (56.43 ± 21.10 ppb). OVOCs, aromatics, halides, alkenes, and alkynes contributed 18.7%, 9.6%, 9.3%, 5.2% and 1.9%, respectively. The observational site shifted from a typical VOC control regime to a mixed regime from May to July, which can be explained by the significant increase of ROx production, resulting in the transition of environment from NOx saturation to radical saturation with respect to O3 production. The optimal O3 control strategy should be dynamically changed depending on the transition of control regime. Under NOx saturation condition, minimizing the proportion of NOx in reduction could lead to better achievement of O3 alleviation. Under mixed control regime, the cut percentage gets the top priority for the effectiveness of O3 control. Five VOCs sources were identified: temperature dependent source (28.1%), vehicular exhausts (19.9%), petrochemical industries (7.2%), solvent & gasoline usage (32.3%) and manufacturing industries (12.6%). The increase of temperature and radiation would enhance the evaporation related VOC emissions, resulting in the increase of VOC concentration and the change of ROx circulation. Our results highlight determination of the optimal control strategies for O3 pollution in a typical YRD industrial city.

Long-term trends of ozone precursors and ozone sensitivity in Jakarta Metropolitan Area: A view from space

Jakarta Metropolitan Area (JMA) is an urban agglomeration in Indonesia where the air quality has dramatically changed from relatively clean to polluted. Economic growth, increased population, and village-to-city expansion marked the development of Jakarta and the satellite cities surrounding it, such as Bogor, Depok, Tangerang, and Bekasi. In line with human activities, large amounts of air pollutants are emitted and affect human health and vegetation. Ozone (O3) is a secondary air pollutant formed from volatile organic compounds (VOCs) and nitrogen oxides (NOx). This study aims to investigate the long-term trend of ozone precursors and ozone sensitivity in JMA from space. Trends analysis is studied using quantile regression. We used NO2 and formaldehyde (HCHO) column density from the Ozone Monitoring Instrument (OMI) aboard Aura Satellite from 2011 to 2022. Ozone sensitivity is derived from the ratio of HCHO and NO2 (FNR). The results show an upward trend in HCHO and a slight NO2 downward over JMA. In general, FNR changed from a predominantly VOC-limited regime in urban JMA to a transitional regime suggesting control of VOC and NOx is needed to reduce ozone concentration. Meanwhile, FNR in suburban and rural areas such as Bogor is toward a more NOx-limited regime.

Elucidating the mechanisms of rapid O3 increase in North China Plain during COVID-19 lockdown period

Ozone (O3) levels in North China Plain (NCP) suffered from rapid increases during the COVID-19 period. Many previous studies have confirmed more rapid NOx reduction compared with VOCs might be responsible for the O3 increase during this period, while the comprehensive impacts of each VOC species and NOx on ambient O3 and their interactions with meteorology were not revealed clearly. To clarify the detailed reasons for the O3 increase, a continuous campaign was performed in a typical industrial city of NCP. Meanwhile, the machine-learning technique and the box model were employed to reveal the mechanisms of O3 increase from the perspective of meteorology and photochemical process, respectively. The result suggested that the ambient O3 level in Tangshan increased from 18.7 ± 4.63 to 45.6 ± 8.52 μg/m3 (143%) during COVID-19 lockdown, and the emission reduction and meteorology contributed to 54 % and 46 % of this increment, respectively. The lower wind speed (WS) coupled with regional transport played a significant role on O3 increase (30.8 kg/s). The O3 sensitivity verified that O3 production was highly volatile organic compounds (VOC)-sensitive (Relative incremental reactivity (RIR): 0.75), while the NOx showed the negative impact on O3 production in Tangshan (RIR: −0.59). It suggested that the control of VOCs rather than NOx might be more effective in reducing O3 level in Tangshan because it was located on the VOC-limited regime. Besides, both of ozone formation potential (OFP) analysis and observation-based model (OBM) demonstrated that the alkenes (36.3 ppb) and anthropogenic oxygenated volatile organic compounds (OVOCs) (15.2 ppb) showed the higher OFP compared with other species, and their reactions released a large number of HO2 and RO2 radicals. Moreover, the concentrations of these species did not experience marked decreases during COVID-19 lockdown, which were major contributors to O3 increase during this period. This study also underlined the necessity of priority controlling alkenes and OVOCs across the NCP.

Impact of spatial scales of control measures on the effectiveness of ozone pollution mitigation in eastern China

Ozone (O3) pollution is becoming the primary air pollution issue with the large decrease in fine particulate concentrations in eastern China. The development of widely recognized policies for controlling O3 pollution episodes is urgent. This study aims to provide actionable and comprehensive suggestions for O3 control policy development, with an emphasis on the precursor emission reductions.Here, we compared the impacts of different spatial scale reductions on a widespread O3 pollution episode in eastern China by a state-of-the-art regional air quality model. We find that region-scale joint control (in >30 cities) is much more effective than city-scale sporadic reduction in reducing O3 concentration. Sporadic controls only reduce the maximum daily 8-h average (MDA8) O3 by ∼1 μg/m3 in the controlled city, whereas regional controls lead to a MDA8 O3 decrease of ∼8 μg/m3 in the controlled region. In addition, the emission reduction effectiveness increased by 2.6 times from <5 cities to >30 cities. Continuous reductions have a cumulative effect on the decrease of MDA8 O3, showing the strongest effects within 24 h and diminishing after 48 h, which underscores the importance of reducing emissions 24 h prior to an episode. Moreover, the effect of control measures on MDA8 O3 varies spatially depending on the ratio of volatile organic compounds (VOCs) to nitrogen oxides (NOx) (VOCs/NOx). Both the reductions of VOC and NOx emissions have a positive effect on the decrease of MDA8 O3 in summer, but the effects of VOC reductions are 1.2 to 1.7 times higher than those of NOx reductions. The residential sector, due to its high VOCs/NOx emission ratio, exhibits the highest efficiency in the reduction of O3 concentrations. Our results highlight the importance of regional joint control and synergistic reduction of VOCs and NOx in eastern China.

Volatile organic compounds during routine production and planned shutdown of a petrochemical refinery: Emission characteristics, source and risk assessment

During the routine production and planned shutdown of a petrochemical refinery in China, ambient volatile organic compound (VOC) data were continuously determined by an online monitoring system, and VOC characteristics, source apportionment, and health risks were calculated based on those data. The data showed that the total VOC concentration emitted during the planned shutdown period was significantly higher than that under daily production conditions, especially the alkane concentration, which increased from 137.4 μg m−3 to 481.8 μg m−3. A source apportionment study was performed using a positive matrix factorization model based on VOC data collected during different sampling times. The contributions of petroleum refinery emissions increased from 63.8% during routine production to 79.4% during the shutdown period. In addition, carcinogenic and noncarcinogenic risk assessment revealed that workers could be under higher acute and chronic health risks during the shutdown and maintenance period than during the routine production of the refinery. The results also indicated that VOCs emitted during maintenance might have more influence on public health. Therefore, more attention should be paid to the emission characteristics and source apportionment of VOCs during planned shutdowns. This work provides valuable data that can help regulatory agencies formulate VOC control strategies during routine production and shutdown maintenance in petrochemical refineries.

Optical absorption enhancement of TiO2 via plasmonic effect of gold nanoparticles in volatile organic compounds medium

Controlling volatile organic compounds (VOC) is of utmost importance due to their adverse impacts on human health and environment. Photocatalytic degradation using TiO2 nanoparticles has emerged as a promising approach for VOC control. However, the limited photocatalytic activity of TiO2 under visible light owing to its wide bandgap presents a significant challenge. To address this limitation, the integration of plasmonic materials with TiO2 enables efficient hot electron injection into TiO2 under visible light. In this study, we investigate the influence of gold nanoparticles (AuNP) on TiO2-based structures, namely AuNP-decorated TiO2 thin films, Au@TiO2 core@shell structures, and AuNP-loaded TiO2 nanoparticles, using finite difference time domain (FDTD) simulations. Simulation results demonstrate that the presence of AuNP in TiO2 structures reduces the bandgap and enhances light absorption. Moreover, the localized electric field enhancement observed at the AuNP-TiO2 interface indicates the potential for effective hot electron injection into TiO2. Additionally, simulations conducted in a VOC medium demonstrate higher absorption compared to vacuum conditions. This work provides insights into the mechanisms underlying previously published experiments and proposes an appealing design for the development of highly efficient photocatalytic materials under visible light.

Climate co-benefits of VOC control policies in China based on a cross-scale approach

Volatile organic compounds (VOC) contributing to smog formation, have been an important indicator of atmospheric governance during China's “14th Five-Year Plan”. VOC would be possibly incorporated into the scope of environmental protection tax, but previous studies have seldom explored impacts of VOC control policies at national and regional levels. Here, we design a national uniform VOC control policy, as well as two regionally differentiated policies based on regional disparities in PM2.5 concentrations and energy intensity by using a cross-scale dynamic computable general equilibrium (CGE) model. Our analysis is to assess the impacts of these policies on VOC, CO2, sulfur dioxide (SO2), nitrogen oxides (NOX), and PM2.5 emissions, air quality and environmental equity, and to estimate health benefits, policy costs and net benefits. We find that national and regionally differentiated VOC control policies generally lead to VOC emission reductions and generate co-benefits on emission reductions in CO2, SO2, NOX and PM2.5 at national and provincial levels. However, regional emission leakage exists due to differences in the provincial costs of VOC mitigation. The regionally differentiated VOC pricing policies are found to be more effective to enhance environmental equity than the uniform policy. In particular, the regionally differentiated VOC control policy based on provincial energy efficiency is found to be superior to other policies in terms of improve air quality. Furthermore, the human health benefits associated with VOC pricing policies would partially offset policy costs at both the national and regional levels. Our results suggest that policymakers would pay attention to developing regions with low energy efficiency which have the great emission reduction potential. Advanced producing technology and further end-of-pipe control measures to reduce non-combustion PM2.5 emissions are needed. VOC policy designed based on provincial energy efficiency provides great insights for environmental policy making to accomplish 2035 goal of building a Beautiful China.

Real-world emission characteristics and inventory of volatile organic compounds originating from construction and agricultural machinery

Volatile organic compound (VOC) emissions originating from nonroad mobile sources constitute an important but uncertain source of secondary organic aerosols (SOAs) and ozone (O3). In this study, we investigated the emission factors (EFs) of 120 individual VOC species for 40 machines via gas chromatography–mass spectrometry/flame ionization detection and high-performance liquid chromatography. The results showed that the diesel-based VOC EF for the tested machines was 4.18 ± 2.55 (average ± standard deviation) g/kg fuel, dominated by alkanes (38.20 % ± 18.08 %) and oxygenated VOCs (OVOCs; 30.94 % ± 15.71 %). The machine type, rated power, emission standards, and operating conditions affected the emissions of VOCs and their components, and this effect maybe mostly depends on the fuel combustion efficiency. The VOC species were primarily distributed in the C1–C2 and C4–C6 (based on the carbon number) and B4–B6 (based on the saturated vapor concentration) intervals. Furthermore, the estimated formation potential (FP) values of SOAs and O3 from VOCs were 21.02 ± 15.57 mg/kg fuel and 15.96 ± 11.87 g/kg fuel, respectively. VOC control based on the SOA formation potential (SOAFP) and ozone formation potential (OFP) could be more effective in the mitigation of fine particulate matter (PM2.5) and O3 pollution because the top 5 species ranked by percentage contribution accounted for 83.09 % ± 9.59 % and 51.78 % ± 14.38 % of the estimated SOAFP and OFP, respectively. Finally, the emission estimates showed that the VOC emissions originating from construction and agricultural machinery in China (2020) reached 64.05 and 95.24 Gg, respectively. We provide species-specific VOC EFs and detailed emission characteristics to facilitate a comprehensive understanding of gas emissions originating from nonroad mobile sources and an update of emission inventories and atmospheric chemistry models.

Development of a CMAQ–PMF-based composite index for prescribing an effective ozone abatement strategy: a case study of sensitivity of surface ozone to precursor volatile organic compound species in southern Taiwan

Abstract. Photochemical ozone pollution is a serious air quality problem under weak synoptic conditions in many areas worldwide. Volatile organic compounds (VOCs) are largely responsible for ozone production in urban areas where nitrogen oxide (NOx) mixing ratios are high while usually not a limiting precursor to ozone (O3). In this study, the Community Multiscale Air Quality model higher-order decoupled direct method (CMAQ-HDDM) at an urban-scale resolution (1.0 km×1.0 km) in conjunction with positive matrix factorization (PMF) was used to identify the dominant sources of highly sensitive VOC species to ozone formation in southern Taiwan, a complex region of coastal urban and industrial parks and inland mountainous areas. First-order, second-order, and cross sensitivities of ozone concentrations to domain-wide (i.e., urban, suburban, and rural) NOx and VOC emissions were determined for the study area. Negative (positive) first-order sensitivities to NOx emissions are dominant over urban (inland) areas, confirming ozone production sensitivity favors the VOC-limited regime (NOx-limited regime) in southern Taiwan. Furthermore, most of the urban areas also exhibited negative second-order sensitivity to NOx emissions, indicating a negative O3 convex response where the linear increase of O3 from decreasing NOx emissions was largely attenuated by the nonlinear effects. Due to the solidly VOC-limited regime and the relative insensitivity of O3 production to increases or decreases of NOx emissions, this study pursued the VOC species that contributed the most to ozone formation. PMF analysis driven by VOCs resolved eight factors including mixed industry (21 %), vehicle emissions (22 %), solvent usage (17 %), biogenic sources (12 %), plastic industry (10 %), aged air mass (7 %), motorcycle exhausts (7 %), and manufacturing industry (5 %). Furthermore, a composite index that quantitatively combined the CMAQ-HDDM sensitivity coefficient and PMF-resolved factor contribution was developed to identify the key VOC species that should be targeted for effective ozone abatement. Our results indicate that VOC control measures should target (1) solvent usage for painting, coating and the printing industry, which emits abundant toluene and xylene; (2) gasoline fuel vehicle emissions of n-butane, isopentane, isobutane, and n-pentane; and (3) ethylene and propylene emissions from the petrochemical industry.