Non-methane Hydrocarbon Emissions Research Articles

Observation-constrained kinetic modeling of isoprene SOA formation in the atmosphere

Abstract. Isoprene has the largest global non-methane hydrocarbon emission, and the oxidation of isoprene plays a crucial role in the formation of secondary organic aerosol (SOA). Two primary processes are known to contribute to SOA formation from isoprene oxidation: (1) the reactive uptake of isoprene-derived epoxides on acidic or aqueous particle surfaces and (2) the absorptive gas–particle partitioning of low-volatility oxidation products. In this study, we developed a new multiphase condensed isoprene oxidation mechanism that includes these processes with key molecular intermediates and products. The new mechanism was applied to simulate isoprene gas-phase oxidation products and SOA formation from previously published chamber experiments under a variety of conditions and atmospheric observations during the Southern Oxidant and Aerosol Studies (SOAS) field campaign. Our results show that SOA formation from most of the chamber experiments is reasonably reproduced using our mechanism, except when the concentration ratios of initial nitric oxide to isoprene exceed ∼ 2, the formed SOA is significantly underpredicted. The SOAS simulations also reasonably agree with the measurements regarding the diurnal pattern and concentrations of different product categories, while the total isoprene SOA remains underestimated. The molecular compositions of the modeled SOA indicate that multifunctional low-volatility products contribute to isoprene SOA more significantly than previously thought, with a median mass contribution of ∼ 57 % to the total modeled isoprene SOA. However, this contribution is intricately intertwined with IEPOX-derived SOA (IEPOX: isoprene-derived epoxydiols), posing challenges for their differentiation using bulk aerosol composition analysis (e.g., the aerosol mass spectrometer with positive matrix factorization). Furthermore, the SOA from these pathways may vary greatly, mainly dependent on the volatility estimation and treatment of particle-phase processes (i.e., photolysis and hydrolysis). Our findings emphasize that the various pathways to produce these low-volatility species should be considered in models to more accurately predict isoprene SOA formation. The new condensed isoprene chemical mechanism can be further incorporated into regional-scale air quality models, such as the Community Multiscale Air Quality Modelling System (CMAQ), to assess isoprene SOA formation on a larger scale.

Effect of split injection strategy of diesel fuel on multi-stage heat release and performance of a RCCI engine fueled with diesel and natural gas

Reactivity controlled compression ignition (RCCI) combustion is a advanced low temperature combustion concept to reduce CO2 and brake the trade-off between NOx and PM emissions for next generation compression ignition (CI) engines. However, it leads to the more complex multi-stage heat release in diesel/natural gas (NG) dual fuel engines and is criticized for extra-high methane and carbon monoxide emissions. Using the existing methods, it is difficult to effectively quantify the contribution of the accumulated heat release (AHR) at each stage to the whole combustion process and to create their relevance to the performance and emissions in the RCCI engines.In this paper, experiments were conducted on a ship diesel/NG dual-fuel engine at a load of 25 %. A new identification and quantitative analysis method of multi-stage heat release is proposed, and the coupling effects of the diesel split injection parameters on the multi-stage heat release and performance in the RCCI engine were revealed. The results show that the new method is not only available for analyzing the combustion of traditional CI engines but also is more effective for identifying the multi-stage combustion in RCCI engines. For the increased pre-injection ratio (PR), as the start of first injection (SOI-I) and the start of second injection (SOI-II) advance, the AHR in Stage-I (Q-Stage-I) decreases, and the increased Q-Stage-III lead to the improved indicated thermal efficiency (ITE > 49 %). Meanwhile, methane (CH4), non-methane hydrocarbon (NMHC) and carbon monoxide (CO) emissions can be reduced by more than 50 %, while nitrogen oxides (NOx) emissions increase. The impact significance of SOI-II on Q-Stage-I and Q-Stage-III is higher, their values are + 65.88 % and −51.04 %, respectively, and the Q-Stage-II is mainly controlled by SOI-I. The impact significance of Q-Stage-III on ITE is the highest about + 69.43 %. Q-Stage-I shows a higher positive correlation with CH4, NMHC and CO emissions although the proportion of Q-Stage-I is far smaller than that of Q-Stage-II and Q-Stage-III. Therefore, the simultaneous reduction of incomplete combustion products and NOx emission can be achieved by reasonably adjusting split injection parameters.

Non-methane hydrocarbons from integrated semiconductor manufacturing processes: Assessments of chemical footprints, emissions factors, and treatment efficiency

Non-methane hydrocarbons (NMHCs) are harmful chemicals produced from organic solvent use in industrial sectors. Wafer fabrication process from semiconductor fabs utilizes many organic solvents that could intensify NMHCs emissions. This study comprehensively assessed the Total NMHCs (TNMHCs) emissions from 141 exhaust pipes of 59 semiconductor fabs in Taiwan with regards to their concentrations, emission factors, treatment efficiency, and total chemical footprint (ChF) for human toxicity. Throughout three semi-processes of wafer fabrication, the raw emitted NMHCs concentrations were in the ranges of 3–131.25 ppm, 8–288 ppm, and 23–567 ppm for wafer cleaning (WC), photoresist stripping (PS), and photolithography (PL). The average untreated TNMHCs emissions rate was 0.2 ± 0.08 kg/h < 1.72 ± 0.09 kg/h < 2.55 ± 0.08 kg/h in the order of WC < PS < PL, whereas the average treated emissions rates were in the ranges of 0.09–0.10 kg/h. The estimated emission factors for wafer fabrication process were 0.30 ± 0.04 kg/kg, 0.07 ± 0.02 kg/piece, and 1.37 ± 0.11 kg/m2. Further assessment has found that zeolite rotary concentrator and regenerative thermal oxidations (ZRC + RTO) possess the highest overall performances for abating TNMHCs emission with efficiency ranges of 92.31–99.56% (n = 66). ZRC + RTO could produce outlet TNMHCs within the ranges of 2.94–5.56 ppm, which were lower than the upcoming revised emission standard of <14 ppm. ChF analysis of the estimated NMHCs species showed that PL had the largest untreated ChF, followed by PS, and WC of which the ChF were 15.72, 7.05, and 6.79 cases. The speciated ChF was dominated by acetone, methanol, and isopropyl alcohol from three semi-processes. The ChF analysis in this study could potentially become a supporting instrument for industrial sectors to determine the major contributing processes and chemicals with adverse impacts to human health.

Research on the results of the WLTP procedure for a passenger vehicle

The article considers variables registered in the WLTP procedure. The test results of a passenger car with a compression-ignition engine have been analysed. The tests were carried out on a chassis dynamometer. The tests were performed for engine cold start and ran up to the point of reaching stabilized operating conditions. The average specific distance emissions and volumetric fuel consumption were assessed for individual test phases as well as for the entire test. It was found that the results in the first test phase, which corresponded to the engine cold start up to stabilized operating conditions, had the most significant impact on the overall exhaust emission and fuel consumption results in the test. The specific distance emissions of carbon monoxide, non-methane hydrocarbons and nitrogen oxides were by far the highest in the first phase of the test. In the fourth phase of the test, the specific distance emissions of methane and carbon dioxide turned out to be the highest, as well as the operational volumetric fuel consumption being the highest.

Influence of the Use of EtG Synthetic Fuel in Spark-Ignition Engines on Vehicle Fuel Consumption and Pollutant Emissions

This article presents the properties of EtG synthetic fuel (Ethanol to Gasoline) as a substitute for fuels in an installation using ethanol from food waste as a raw material. The results of this research on the process of supplying the engine with EtG fuel are presented, in which the operational suitability of this fuel was verified, including environmental requirements. The results of pollutant emission tests from vehicles with spark-ignition engines in dynamic driving conditions in the New European Driving Cycle (NEDC) type approval tests and the World Harmonized Test Cycle (WLTC) test, both on a “cold” and “hot engine”, are presented. It was found that EtG fuel is characterized by lower emissions of carbon monoxide, nitrogen oxides, and methane, and higher emissions of non-methane hydrocarbons compared to E10 commercial gasoline, while the specific distance emission of carbon dioxide for both fuels was very similar.

Experimental investigation on exhaust emissions of a heavy-duty vehicle powered by a methanol-fuelled spark ignition engine under world Harmonized Transient Cycle and actual on-road driving conditions

Compared to the conventional fossil fuels, methanol is a renewable, environment-friendly, and inexpensive oxygenated fuel. In this work, to explore the feasibility of using methanol as a substitute for diesel or gasoline in internal combustion engines, the exhaust emissions of a heavy-duty vehicle powered by the methanol spark ignition (SI) engine are tested under the World Harmonized Transient Cycle (WHTC) and actual on-road driving conditions. The results indicate that the brake specific CO, NOx, PM, and non-methane hydrocarbon emissions of the heavy-duty engine fuelled with methanol under the WHTC are lower than those of the engine fuelled with diesel and diesel-gasoline. However, the NH3 emission of the heavy-duty engine fuelled with natural gas is much higher than that of the methanol-fuelled engine, and exceeds the China VI emission standard. Under the actual road test, CO emission decreases once the exhaust temperature of the test vehicle reaches up to 250 °C, while NOx emissions are maintained at a relatively low level and then sharply increase at the initial cold-start of the road test. However, NOx emissions increase with further increase in the exhaust temperature.

Advanced Catalytic Technologies for Compressed Natural Gas–Gasoline Fuelled Engines

The main challenges of compressed natural gas (CNG) engine fuelling in terms of methane abatement in the aftertreatment system are addressed in this study using differently loaded platinum group metal (pgm) catalysts. A dual-fuel injection strategy of methane-gasoline was implemented where methane gas was port-injected into the intake in stoichiometric conditions at levels corresponding to 20% and 40% energy density replacement of gasoline fuel. High, medium and low loaded palladium-rhodium catalysts were used and compared to study the effect of pgm loading on the catalyst light-off activity for methane. Results indicate that increasing the palladium loading led to significantly earlier light-off temperatures achieved at relatively lower temperatures of 340°C, 350°C and 395°C respectively. However, the benefit diminishes above palladium loading &gt;142.5 g ft–3. The study has also demonstrated that ammonia is formed over the CNG catalyst due to steam-reforming reactions from the increased levels of methane in the exhaust with dual-fuelling. Hence aftertreatment technologies such as selective catalytic reduction (SCR) should be adopted to remove them. This further highlights the need to regulate the harmful ammonia emissions from future passenger cars fuelled with CNG. In addition, the benefits of the dual-fuel system in terms of lower engine output carbon dioxide, non-methane hydrocarbon (NMHC) and particulate matter (PM) emissions compared to the gasoline direct injection (GDI) mode alone are presented.

Characteristics and emissions of isoprene and other non-methane hydrocarbons in the Northwest Pacific Ocean and responses to atmospheric aerosol deposition

Field investigations in the Northwest Pacific Ocean were carried out to determine the distributions of marine and atmospheric non-methane hydrocarbons (NMHCs), sources and environmental effects. We also conducted deck incubation experiments to investigate the effects of atmospheric aerosol deposition on NMHCs production. The marine NMHCs displayed an increasing trend from the South Equatorial Current to the Oyashio Current. The enhanced phytoplankton biomass and dissolved organic materials (DOM) content in the Kuroshio-Oyashio Extension contributed significantly to isoprene and NMHCs production compared with those in tropical waters and the North Pacific subtropical gyre. The Northwest Pacific Ocean was a significant source of atmospheric NMHCs, with average sea-to-air fluxes of 28.0 ± 38.9, 65.2 ± 73.3, 21.0 ± 26.7, 48.7 ± 62.6, 12.7 ± 15.9, 14.2 ± 16.8, and 41.7 ± 80.4 nmol m−2 d−1 for ethane, ethylene, propane, propylene, i-butane, n-butane, and isoprene, respectively. Influenced by seawater release and OH radical consumption, the atmospheric NMHCs apart from isoprene displayed upward trends with increasing latitude. The deck incubation showed that the addition of aerosols and acidic aerosols significantly boosted phytoplankton biomass, altered community structure, and accelerated the production of isoprene. However, the other six NMHCs showed no obvious responses to atmospheric aerosol deposition in the incubation experiments. In summary, ocean current movements and atmospheric deposition could influence the production and release of isoprene in the Northwest Pacific Ocean.

The contributions of non-methane hydrocarbon emissions by different fuel type on-road vehicles based on tests in a heavily trafficked urban tunnel

Automobile exhaust is a major source of volatile organic compounds (VOCs) in metropolitan areas, yet it is difficult to accurately determine the contributions of different types of on-road vehicles. Tunnel tests are an effective way to measure real-world vehicle emissions, and the data collected are also suitable for receptor modeling to analyze the contributions of non-methane hydrocarbons (NMHCs) from different types of vehicles, as the closed environment ensures good mixing and minimal aging. In this study, tunnel tests were conducted inside a heavily trafficked city tunnel in Guangzhou in south China, and the positive matrix factorization (PMF) model was applied to the inlet-outlet incremental NMHC data. The results revealed that gasoline vehicles (GVs), Liquefied Petroleum Gas vehicles (LPGVs), and diesel vehicles (DVs) were responsible for 39 %, 45 % and 16 % of NMHCs, and 52 %, 23 %, and 24 % of the ozone formation potentials, respectively. LPGVs were the largest contributor of (56 %) alkanes, and GVs were the largest contributor of aromatics (61 %) and C2-C4 alkenes (55 %). With the video-recorded traffic counts the emissions of different fuel types are further compared on a per-vehicle-per-kilometer basis, and the results reveal that LPGVs and GVs were comparable in the OFPs of NMHCs emitted per kilometer, while on average a DV emitted 2.0 times more NMHCs than a GV with 2.4 times more OFPs. This study highlights substantial contribution of reactive alkenes and aromatics by DVs and the benefits of strengthening diesel exhaust control in terms of preventing ozone pollution.

Diurnal variation and source analysis of NMHCs at a background site of Nam Co (4,730 m a.s.l.) in the interior area of Tibetan Plateau

As the highest plateau in the world, the atmospheric environment of the Tibetan Plateau (TP) has a significant influence on the continental and global climate. The non-methane hydrocarbon (NMHC) characteristics at the background site Nam Co (4730 m a.s.l.) on the TP were investigated based on the concentration characteristics, diurnal variations, emission source identification, and transport pathways in the summer of 2020. The concentration of NMHC at the sampling site was 3408 pptv, which was lower than most of global background sites. The diurnal variations in the NMHC concentration at the sampling site were higher at night and noon and lower in the morning and afternoon, which was quite different from that in urban areas. Positive matrix factorization (PMF) and HYSPLIT models were used to identify the NMHC emission sources. The PMF model identified regional transport (40.2%), biomass burning (23.6%), vehicle emissions (22.0%), and biogenic sources (14.2%) as the predominant NMHC sources. The HYSPLIT model indicated the air masses over the sampling site could be clustered in three directions. The analysis of the potential source contribution function (PSCF) and concentration-weighted trajectory (WCWT) indicated the NMHC concentration at the sampling site was primarily influenced by air masses from the southern Tibet. The health risk assessment signified the benzene levels were high enough to cause a potential cancer risk during the sampling period. Research on the NMHC characteristics of background sites could provide the basis for studying the NMHC transport pathway between regions and the global atmospheric motions.

Emissions of gaseous pollutants released by forest fire in relation to litter fuel moisture content

The moisture content of forest floor fuel influences fire initiation and spread, but little is known about its impact on the emissions of pollutants. This study aimed to estimate quantitatively the characteristic change of pollutants emitted by forest fires at various fuel moisture content. Thus, litter fuel (both branches and leaves) of two dominant coniferous species (Cunninghamia lanceolata and Pinus massoniana) and two dominant broad-leaved species (Eucalyptus robusta and Cinnamomum camphora) in Southeast China were experimentally burned in an indoor biomass combustion facility, and smoke and non-methane hydrocarbons (NMHCs) were analyzed by gas chromatography-mass spectrometry. The results showed that CO, CO2, NOx, and SO2 reached peak concentrations faster at low moisture content. However, emission factors of CO increased, whereas emission factors of CO2, NOx, and SO2 decreased as the moisture content of fuels increased. Emission factors of CO, CO2, NOx and SO2 released from combustion of conifer fuels significantly increased with fuel moisture content compared to broad-leaved fuels. Total NMHCs emission was positively affected by the fuel moisture content. As the moisture content of the fuels increased, multi-branched and long-chain alkane emissions increased, whereas olefin and aromatic hydrocarbon emissions decreased but emissions of olefins and aromatic hydrocarbons with more branched chains increased. The findings provide valuable insight about the impact of forest fire on atmospheric environment and fire prevention measures.

Airborne Trace Gas Remote Sensing and Surface Mobile In Situ: A Novel Tool for the Study of Structural Geological Controls from a Producing Oil Field

SummaryAccurate and representative determination of greenhouse gases (GHG) from oil and gas (O&amp;G) production facilities requires high-spatial-resolution data, which can be acquired by airborne imaging spectrometers. However, assessment of nonmethane hydrocarbon emissions, which are far less amenable to remote sensing, requires mobile surface in-situ measurements (e.g., a mobile air quality laboratory).Field in-situ measurements and airborne thermal infrared spectral imagery were acquired for three producing California oil fields (Poso Creek, Kern Front, and Kern River) located next to each other on 14 September 2018. In addition, a profile ascending a nearby mountain collected in-situ data for the Round Mountain oilfield. Plume methane to ethane ratios were consistent within different regions of the field and differed between these fields in a manner related to field geological structures.Data acquired by an airborne thermal infrared imaging spectrometer, Mako, in 2015 and 2018 showed most emissions were from distant plumes in the Kern Front and Poso Creek fields. The spatial distribution of detected plumes was strongly related to faults, particularly active faults, which are proposed to stress infrastructure, leading to higher fugitive emissions and/or emissions from natural migration pathways (seepage). Additionally, the spatial distribution of detected plumes suggested unmapped faults. Thus, high-sensitivity imaging spectroscopy can improve understanding of reservoir geological structures that impact hydrocarbon migration and field operations, highlighting the potential for a novel reservoir management tool.

Emissions of non-methane hydrocarbons and typical volatile organic compounds from various grate-firing coal furnaces

Non-methane hydrocarbons (NMHCs) and volatile organic compounds (VOCs) emitted from grate-firing coal furnaces cause serious harmful impacts on the atmospheric environment and human health. To investigate the effects of coal type and grate-firing mode on the emissions of NMHCs and VOCs, four different coal fuels (i.e., bituminous coal (BC), bituminous briquette (BB), anthracite briquette (AB) and semi-coke (SC)) were burnt in three typical grate-firing modes (i.e., updraft mode (UDM), downdraft mode (DDM) and cross-draft mode (CDM)). Offline GC-MS (Gas Chromatography-Mass Spectrometry) analyses show that the mass of benzene and toluene accounts for more than 60% of the total amount of quantifiable benzenoid compounds under the smoldering condition, and up to almost 100% under the flaming condition. The BB burnt in the CDM produces lower NMHCs and VOCs than in the other two modes and the SC burnt in the three modes yields the lowest NMHCs and VOCs among the four coal fuels, as further clarified by online FTIR (Fourier-Transform Infrared spectroscopy) measurements. Combustion mode was found to have a prominent impact on the NMHCs and VOCs emissions in household coal stoves. The NMHCs emission factor determined by the GC-MS measurements under the flaming and smoldering stages is inversely proportional to combustion efficiency. The average VOCs emission factor calculated from the FTIR measuring data inversely varies with combustion efficiency too.

Observation-based sources evolution of non-methane hydrocarbons (NMHCs) in a megacity of China

Both concentrations and emissions of many air pollutants have been decreasing due to implement of control measures in China, in contrast to the fact that an increase in emissions of non-methane hydrocarbons (NMHCs) has been reported. This study employed seven years continuous NMHCs measurements and the related activities data of Shanghai, a megacity in China, to explore evolution of emissions and effectiveness of air pollution control measures. The mixing ratio of NMHCs showed no statistical interannual changes, of which their compositions exhibited marked changes. This resulted in a decreasing trend of ozone formation potential by 3.8%/year (p < 0.05, the same below), which should be beneficial to ozone pollution mitigation as its production in Shanghai is in the NMHCs-limited regime. Observed alkanes, aromatics and acetylene changed by +3.7%/year, -5.9%/year and -7.4%/year, respectively, and alkenes showed no apparent trend. NMHCs sources were apportioned by a positive matrix factorization model. Accordingly, vehicular emissions (-5.9%/year) and petrochemical industry emissions (-7.1%/year) decreased significantly, but the decrease slowed down; significant reduction in solvent usage (-9.0%/year) appeared after 2010; however, emissions of natural gas (+12.6%/year) and fuel evaporation (with an increasing fraction) became more important. The inconsistency between observations and inventories was found in interannual trend and speciation as well as source contributions, emphasizing the need for further validation in NMHCs emission inventory. Our study confirms the effectiveness of measures targeting mobile and centralized emissions from industrial sources and reveals a need focusing on fugitive emissions, which provided new insights into future air policies in polluted region.

Tower-based measurements of NMHCs and OVOCs in the Pearl River Delta: Vertical distribution, source analysis and chemical reactivity

Measurements of vertical distribution of volatile organic compounds (VOCs) have attracted wide attentions, which could help to understand atmospheric oxidation mechanism and provide implications for VOC control. This study measured the non-methane hydrocarbons (NMHCs) and oxygenated VOCs (OVOCs) simultaneously for the first time at three different heights, namely ground, 118 m and 488 m, in the Canton Tower located in the urban core of the Pearl River Delta (PRD). The results show that NMHCs decreased while some OVOC species such as formaldehyde and acetaldehyde increased with increasing height. It was mainly attributed to the dilution and chemical loss of NMHCs but secondary production of OVOCs during vertical transport. Ratio analysis and receptor modeling indicate that vehicle exhausts (47%) and fuel evaporation (39%) were major sources of the total NMHCs. Interestingly, industry contributed much more at 118 m, probably affected by organic gas discharge from the high chimney of industrial factories. The chemical reactivities in terms of OH radical loss rate (LOH), ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) were lowest at 118 m, smaller than those influenced by high fresh NMHC emissions at ground and strong formation of secondary species (e.g. OVOCs) at 488 m. OH exposure estimated by isoprene and m,p-xylene/ethylbenzene was different depending on their time scale of vertical turbulent mixing and chemical loss. OVOC species measured at different heights were positively correlated with Ox (R = 0.48–0.87), indicating that OVOCs were largely contributed by secondary formation in photochemical process. The tower measurements of NMHCs and OVOCs provided a unique opportunity to investigate the VOC distribution and chemical behaviors, which could give important information for understanding O3 and PM2.5 pollution mechanism in the PRD region with fast developing urban setting and substantially changing air quality.

Emission Characteristics of Hazardous Air Pollutants from Medium-Duty Diesel Trucks Based on Driving Cycles

Studies on the characteristics of hazardous air pollutants (HAPs) in the emissions of medium-duty diesel trucks are significantly insufficient compared to those on heavy-duty trucks. This study investigated the characteristics of regulated pollutants and HAPs, such as volatile organic compounds (VOCs), aldehydes, and polycyclic aromatic hydrocarbons (PAHs), and estimated non-methane hydrocarbon (NMHC) speciation in the emissions of medium-duty diesel trucks. Ten medium-duty diesel trucks conforming to Euros 5 and 6 were tested for four various driving cycles (WLTC, NEDC, CVS-75, and NIER-9) using a chassis dynamometer. In an urban area such as Seoul, CO and NMHC emissions were increased because of its longer low-speed driving time. NOx emissions were the highest in the high-speed phase owing to the influence of thermal NOx. PM emissions were almost not emitted because of the DPF installation. Alkanes dominated non-methane volatile organic compound (NMVOC) emissions, 36–63% of which resulted from the low reaction of the diesel oxidation catalyst. Formaldehyde emissions were the highest for 35–53% among aldehydes irrespective of driving cycles. By sampling the particle-phase of PAHs, we detected benzo(k)fluoranthene and benzo(a)pyrene and estimated the concentrations of the gas-phase PAHs with models to obtain the total PAH concentrations. In the particle portion, benzo(k)fluoranthene and benzo(a)pyrene were over 69% and over 91%, respectively. The toxic equivalency quantities of benzo(k)fluoranthene and benzo(a)pyrene from NIER-9 (cold) for both Euro 5 and Euro 6 vehicles were more than five times higher than those of NIER (hot) and NEDC. In the case of NMHC speciation, formaldehyde emissions were the highest for 10–45% in all the driving cycles. Formaldehyde and benzene must be controlled in the emissions of medium-duty diesel trucks to reduce their health threats. The results of this study will aid in establishing a national emission inventory system for HAPs of mobile sources in Korea.

Comparison of vehicle emissions by EMFAC-HK model and tunnel measurement in Hong Kong

On-road vehicular emissions were measured in a Hong Kong roadway tunnel and compared to those from a mobile emission model (EMFAC-HK) for the 2003 and 2015 fleets to assess emission changes and effectiveness of emission controls. EMFAC-HK results compared well with tunnel measurement for the 2015 fleet with differences ≤50% for most pollutants. Both measurement and modeled estimates show that non-methane hydrocarbon (NMHC) and PM2.5 decreased by over 40% from 2003 to 2015. Tunnel measurements also show that nitrogen dioxide (NO2) and liquefied petroleum gas (LPG) -related NMHC emissions increased due to expanded installation of diesel oxidation catalysts and LPG fueling. Motorcycles and LPG-fueled public light buses (3.7% of the fleet) contributed disproportionally high fractions of carbon monoxide (CO; 27%) and NMHC (49%) and deserve additional emission controls. Fuel economy improvements did not result in expected carbon dioxide (CO2) emission reductions, indicating that more aggressive CO2 reductions, particularly from heavy-duty vehicles, are needed.

Air pollutant emissions from the asphalt industry in Beijing, China

Improving our understanding of air pollutant emissions from the asphalt industry is critical for the development and implementation of pollution control policies. In this study, the spatial distribution of potential maximum emissions of volatile organic compounds (VOCs) in the complete life cycle of asphalt mixtures, as well as the particulate matter (PM), asphalt fume, nonmethane hydrocarbons (NMHCs), VOCs, and benzoapyrene (BaP) emissions from typical processes (e.g., asphalt and concrete mixing stations, asphalt heating boilers, and asphalt storage tanks) in asphalt mixing plants, were determined in Beijing in 2017. The results indicated that the potential maximum emissions of VOCs in the complete life cycle of asphalt mixtures were 18,001 ton, with a large contribution from the districts of Daxing, Changping, and Tongzhou. The total emissions of PM, asphalt fume, NMHC, VOCs, and BaP from asphalt mixing plants were 3.1, 12.6, 3.1, 23.5, and 1.9 × 10−3 ton, respectively. The emissions of PM from asphalt and concrete mixing stations contributed the most to the total emissions. The asphalt storage tank was the dominant emission source of VOCs, accounting for 96.1% of the total VOCs emissions in asphalt mixing plants, followed by asphalt heating boilers. The districts of Daxing, Changping, and Shunyi were the dominant regions for the emissions of PM, asphalt fume, NMHC, and BaP, while the districts of Shunyi, Tongzhou, and Changping contributed the most emissions of VOCs.

The production and hydrolysis of organic nitrates from OH radical oxidation of &amp;lt;i&amp;gt;β&amp;lt;/i&amp;gt;-ocimene

Abstract. Biogenic volatile organic compounds (BVOCs) emitted by plants represent the largest source of non-methane hydrocarbon emissions on Earth. Photochemical oxidation of BVOCs represents a significant pathway in the production of secondary organic aerosol (SOA), affecting Earth's radiative balance. Organic nitrates (RONO2), formed from the oxidation of BVOCs in the presence of NOx, represent important aerosol precursors and affect the oxidative capacity of the atmosphere, in part by sequestering NOx. In the aerosol phase, RONO2 hydrolyze to form nitric acid and numerous water-soluble products, thus contributing to an increase in aerosol mass. However, only a small number of studies have investigated the production of RONO2 from OH oxidation of terpenes, and among those, few have studied their hydrolysis. Here, we report a laboratory study of OH-initiated oxidation of β-ocimene, an acyclic, tri-olefinic monoterpene released during the daytime from vegetation, including forests, agricultural landscapes, and grasslands. We conducted studies of the OH oxidation of β-ocimene in the presence of NOx using a 5.5 m3 all-Teflon photochemical reaction chamber, during which we quantified the total (gas- and particle-phase) RONO2 yield and the SOA yields. We sampled the organic nitrates produced and measured their hydrolysis rate constants across a range of atmospherically relevant pH. The total organic nitrate yield was determined to be 38(±9) %, consistent with the available literature regarding the dependence of organic nitrate production (from RO2 + NO) on carbon number. We found the hydrolysis rate constants to be highly pH dependent, with a hydrolysis lifetime of 51(±13) min at pH = 4 and 24(±3) min at pH = 2.5, a typical pH for deliquesced aerosols. We also employed high-resolution mass spectrometry for preliminary product identification. The results indicate that the ocimene SOA yield (&lt; 1 %) under relevant aerosol mass loadings in the atmosphere is significantly lower than reported yields from cyclic terpenes, such as α-pinene, likely due to alkoxy radical decomposition and formation of smaller, higher-volatility products. This is also consistent with the observed lower particle-phase organic nitrate yields of β-ocimene – i.e., 1.5(±0.5) % – under dry conditions. We observed the expected hydroxy nitrates by chemical ionization mass spectrometry (CIMS) and some secondary production of the dihydroxy dinitrates, likely produced by oxidation of the first-generation hydroxy nitrates. Lower RONO2 yields were observed under high relative humidity (RH) conditions, indicating the importance of aerosol-phase RONO2 hydrolysis under ambient RH. This study provides insight into the formation and fate of organic nitrates, β-ocimene SOA yields, and NOx cycling in forested environments from daytime monoterpenes not currently included in atmospheric models.

Occurrence and emission of non-methane hydrocarbons in the East China Sea: roles of phytoplankton assemblages

Environmental context Marine-derived non-methane hydrocarbons (NMHCs) are thought to affect atmospheric oxidation balance and aerosol formation, hence playing an important role in regulating climate. In this study, we report the distributions and sea-to-air fluxes of 10 NMHCs in the East China Sea (ECS), and assess the roles of phytoplankton assemblages in the occurrence and emission of NMHCs in the ECS. The results will improve our understanding of the biogeochemical cycling of NMHCs in marine systems. Abstract Non-methane hydrocarbons (NMHCs) are important reactive trace-gases that are emitted from oceanic sources. However, it remains unclear how phytoplankton, either total biomass or specific species, affect the generation and emission of NMHCs. This study conducted field observations of NMHCs in the East China Sea (ECS) in autumn, 2014. The mean concentrations of ethane, propane, i-butane, n-butane, pentane, ethene, propene, 1-butene, 1-pentene and isoprene were 20.1 ± 3.6, 20.3 ± 20.2, 4.5 ± 0.9, 10.5 ± 2.3, 14.8 ± 3.4, 63.7 ± 20.8, 23.6 ± 6.6, 7.4 ± 2.9, 15.9 ± 4.3 and 69.4 ± 24.9 pmol L−1 respectively. Horizontal and vertical profiles of NMHCs showed that different water masses had distinct influences and the coastal areas had generally higher concentrations of NMHCs. There were significant positive correlations between alkanes or alkenes, which suggested that their production and fates in the surface seawater were similar. A significant positive correlation was observed between the isoprene and Chl-a concentrations, while no significant correlation was found between Chl-a and any other NMHCs. These results highlighted that, although NMHCs can be produced by phytoplankton, using Chl-a data or phytoplankton assemblages to estimate the production of other NMHCs in seawater is unreliable. Therefore, future research must determine the factors that control the production of these NMHCs. In addition, the results of estimated sea-to-air fluxes of NMHCs underscored the importance of the ECS as a source of NMHCs and the related atmospheric volatile organic compounds.