Comprehensive Assessment for the Impacts of S/IVOC Emissions from Mobile Sources on SOA Formation in China.

Semivolatile/intermediate-volatility organic compounds (S/IVOCs) from mobile sources are essential SOA contributors. However, few studies have comprehensively evaluated the SOA contributions of S/IVOCs by simultaneously comparing different parameterization schemes. This study used three SOA schemes in the CMAQ model with a measurement-based emission inventory to quantify the mobile source S/IVOC-induced SOA (MS-SI-SOA) for 2018 in China. Among different SOA schemes, SOA predicted by the 2D-VBS scheme was in the best agreement with observations, but there were still large deviations in a few regions. Three SOA schemes showed the peak value of annual average MS-SI-SOA was up to 0.6 ± 0.3 µg/m3. High concentrations of MS-SI-SOA were detected in autumn, while the notable relative contribution of MS-SI-SOA to total SOA was predicted in the coastal areas in summer, with a regional average contribution up to 20 ± 10% in Shanghai. MS-SI-SOA concentrations varied by up to 2 times among three SOA schemes, mainly due to the discrepancy in SOA precursor emissions and chemical reactions, suggesting that the differences between SOA schemes should also be considered in modeling studies. These findings identify the hotspot areas and periods for MS-SI-SOA, highlighting the importance of S/IVOC emission control in the future upgrading of emission standards.

Source-Receptor Relationship Revealed by the Halted Traffic and Aggravated Haze in Beijing during the COVID-19 Lockdown.

The COVID-19 outbreak greatly limited human activities and reduced primary emissions particularly from urban on-road vehicles but coincided with Beijing experiencing "pandemic haze," raising the public concerns about the effectiveness of imposed traffic policies to improve the air quality. This paper explores the relationship between local vehicle emissions and the winter haze in Beijing before and during the COVID-19 lockdown based on an integrated analysis framework, which combines a real-time on-road emission inventory, in situ air quality observations, and a localized numerical modeling system. We found that traffic emissions decreased substantially during the COVID-19 pandemic, but its imbalanced emission abatement of NOx (76%, 125.3 Mg/day) and volatile organic compounds (VOCs, 53%, 52.9 Mg/day) led to a significant rise of atmospheric oxidants in urban areas, resulting in a modest increase in secondary aerosols due to inadequate precursors, which still offset reduced primary emissions. Moreover, the enhanced oxidizing capacity in the surrounding regions greatly increased the secondary particles with relatively abundant precursors, which was transported into Beijing and mainly responsible for the aggravated haze pollution. We recommend that mitigation policies should focus on accelerating VOC emission reduction and synchronously controlling regional sources to release the benefits of local traffic emission control.

Intermediate-Volatility Organic Compound Emissions from Nonroad Construction Machinery under Different Operation Modes.

Intermediate-volatility organic compounds (IVOCs) have been found as important sources for secondary organic aerosol (SOA) formation. IVOC emissions from nonroad construction machineries (NRCMs), including two road rollers and three motor graders, were characterized under three operation modes using an improved portable emission measurement system. The fuel-based IVOC emission factors (EFs) of NRCMs varied from 245.85 to 1802.19 mg/kg·fuel, which were comparable at magnitudes to the reported results of an ocean-going ship and on-road diesel vehicles without filters. The discrepancy of IVOC EFs is significant within different operation modes. IVOC EFs under the idling mode were 1.24-3.28 times higher than those under moving/working modes. Unspeciated b-alkanes and cyclic compounds, which were the unresolved components in IVOCs at the molecular level, accounted for approximately 91% of total IVOCs from NRCMs. The SOA production potential analysis shows that IVOCs dominated SOA formation of NRCMs. Our results demonstrate that IVOC emissions from NRCMs are non-negligible. Thus, an accurate estimation of their IVOC emissions would benefit the understanding of SOA formation in the urban atmosphere.

Altitude-dependent gaseous emissions from freight trucks along the China-Pakistan Economic Corridor in Pakistan.

Recent increases in emissions from freight transport have caused strong concerns about air quality in Pakistan, following the rapid development of projects related to the China-Pakistan Economic Corridor (CPEC). This study reported the first measurements of on-road truck emissions in Pakistan and investigated their dependence on altitude along CPEC routes. Emissions from 70 trucks were measured on CPEC highways located in Islamabad (540 m above sea level), Sost (2800 m above sea level), and at the Khunjerab Pass (4693 m above sea level). Calculated emission factors for carbon monoxide, hydrocarbons, and nitrogen oxides from heavy-duty trucks in Islamabad were 12.94 ± 1.46, 15.21 ± 1.67, and 10.69 ± 1.34 g km-1 (95% confidence level), respectively, for pre-Pak-II trucks, and 12.75 ± 2.80, 14.24 ± 3.53, and 10.24 ± 2.34 g km-1 (95% confidence level), respectively, for Pak-II trucks, representing 2-20 times higher values than the emission standards in Pakistan and India. An altitude increase of approximately 4000 m, with the associated changes in meteorology and fleet characteristics, induced an average increase of 103.6%, 86.3%, 124.5%, and 133.6% in the emission factors of carbon monoxide, hydrocarbons, nitrogen oxides, and carbon dioxide, respectively. Moreover, on-road emissions along the CPEC were mainly influenced by truck types. This study will support the budget evaluation of transport emissions from the CPEC trade fleet.

Highly spatial and temporal bottom-up vehicle emission characterization and its control in a typical ecology-preservation area.

The Chishui River Valley is a microscale ecology-preservation area with industrial clusters. The significance of evaluating vehicular emissions has been gradually highlighted with the rapid development of the local transportation and tourism sectors. This study provides the first estimates based on both bottom-up and top-down approaches. The annual total emissions of CO, NOx, hydrocarbons (HC), PM10, and PM2.5 in 2019 were 347.8, 189.6, 46.3, 6.9, and 6.3 Mg, respectively. Trucks contributed the most (55%) to the NOx emissions, followed by heavy-duty passenger vehicles (26%). In contrast, light-duty passenger vehicles and motorcycles generated 75% of the HC emissions. The superior accuracy of highly spatial and temporal bottom-up estimates versus top-down estimates is validated by the similar variation trends of hourly emission intensities and enhanced concentrations relative to background observations for both NOx and CO, with Pearson correlation coefficients between the intensities and concentrations ranging from 0.79 to 0.85. Historical HC emissions peaked in 2013, followed by a sharp decline in 2014 and a continuous rise since then, whereas NOx emissions have kept increasing since 2010. These indicated the necessity and urgency of effective vehicular emission mitigations. Based on scenario analysis, traffic restrictions combined with upgrading the emission standards of admitted vehicles will possess huge emission reduction potentials. Future recommendations about establishing a low emission zone in the valley and supporting policies were introduced.

An updated comprehensive IVOC emission inventory for mobile sources in China.

Intermediate volatility organic compounds (IVOCs) from mobile sources contribute significantly to secondary organic aerosol (SOA) formation. However, the assessments of IVOC emissions remain considerably uncertain due to the lack of localized measured data and detailed emission source classifications. This study established a comprehensive database of IVOC emission factors (EFs) for mobile sources based on the diversified measured EFs and correlations with hydrocarbons. The provincial-level IVOC emission inventories over China were further established by integrating activity data of various mobile sources. The national mobile source IVOC emissions were 507.5 Gg in 2017. The IVOC emissions of on-road and non-road mobile sources were roughly the same. Trucks and non-road construction machineries were the major contributors to IVOC emissions, accounting for >66 % of the total. The IVOC emission characteristics and spatial distributions from various mobile sources varied significantly with different types and usages. The IVOC emission inventories with detailed classifications can be used to evaluate emission control policies for mobile sources. Incorporating localized measured data would be beneficial for a better understanding for the atmospheric impacts of mobile source IVOC emissions.

Molecular characterization of atmospheric particulate organosulfates in a port environment using ultrahigh resolution mass spectrometry: Identification of traffic emissions.

Organosulfates (OSs) are an important component of atmospheric organic aerosol (OA) and are widespread in various environments. However, the OSs generated from anthropogenic emissions are poorly understood. In this study, the molecular compositions of OSs from atmospheric PM2.5 samples collected during a winter measurement campaign (SEISO-Bohai) at Jingtang Harbor were characterized via ultrahigh resolution mass spectrometry (UHRMS). The changes of port OS compositions were observed in episodes of complete haze pollution. As the pollution aggravated, the relative abundances of OSs were apparently increased, and the molecule compositions became more complex, primarily driven by the oxidation and fragmentation processes. Potential OS precursors from traffic emissions were identified based on an optimized "OS precursor map" developed in the previous study. OSs characterized by high molecular weights and low degrees of both unsaturation and oxidization were suggested to mainly derive from secondary reactions of intermediate volatile organic compounds (IVOCs) emitted by traffic sources. These OSs were primarily detected in clean-day samples, followed by decreasing with the pollution process. In addition, our study also finds that ship emissions may further facilitated OS productions under haze pollution conditions.

Road freight emission in China: From supply chain perspective.

Freight emissions management has entered the deep-water zone. This study evaluated road freight emissions from supply chain perspective using China's 2007, 2010 and 2012 multiregional input-output table. For the first time, we quantified road freight emission based on sectors in China. Heavy industries, mining, agriculture and light industry contributed 71%,14%, 12% and 3% of total NOx emissions in 2012 from production perspective. Construction was the largest consumption sector (43%) responsible for road freight emission from consumption perspective. Upstream transport and final product transport emitted 3.04 Tg (80%) and 0.77 Tg (20%) NOx in 2012. Huge disparities of road freight emissions flows and allocation patterns were found across provinces in China in terms of resource endowments, geographical position and economic development. The road freight emission increased rapidly from 2007 to 2012, and economic growth effect outpaced emission control effect caused by emission standard upgrade and thus dominated the emission growth. The production structure and consumption pattern changes also promoted the emission growth. It is thus important to mitigate freight emissions with different strategies based on a certain sector's freight emissions features from the whole supply chain.

Primary organic gas emissions from gasoline vehicles in China: Factors, composition and trends.

Continuous tightening emission standards (ESs) facilitate the reduction of organic gas emissions from gasoline vehicles. Correspondingly, it is essential to update the emissions and chemical speciation of total organic gases (TOGs), including volatile organic compounds (VOCs), intermediate volatility organic compounds (IVOCs), CH4, and unidentified non-methane hydrocarbons (NMHCs) for assessing the formation of ozone and secondary organic aerosol (SOA). In this study, TOG and speciation emissions from 12 in-use light-duty gasoline vehicle (LDGV) exhausts, covering the ESs from China II to China V, were investigated on a chassis dynamometer under the Worldwide Harmonized Light-duty Test Cycle (WLTC) in China. The results showed that the most effectively controlled subgroup in TOG emissions from LDGVs was VOCs, followed by the unidentified NMHCs and IVOCs. The mass fraction of VOCs in TOGs also reduced from 61 ± 9% to 46 ± 18% while the IVOCs gently increased from 2 ± 0.4% to 8 ± 4% along with the more stringent ESs. For the VOC subsets, the removal efficiency of oxygenated VOCs (OVOCs) was lower than those of other VOC subsets in the ESs from China IV to V, suggesting the importance of OVOC emission controls for relatively new LDGVs. The IVOC emissions were mainly subject to the ESs, then driving cycles and fuel use. The formation potentials of ozone and SOA from LDGVs decreased separately 96% and 90% along with the restricted ESs from China II-III to China IV. The major contributor of SOA formation transformed from aromatics in the VOC subsets for China II-III vehicles to IVOCs for China IV/V vehicles, highlighting that IVOC emissions from LDGVs are also needed more attentions to control in future.

A big data approach to improving the vehicle emission inventory in China.

Estimating truck emissions accurately would benefit atmospheric research and public health protection. Here, we developed a full-sample enumeration approach TrackATruck to bridge low-frequency but full-size vehicles driving big data to high-resolution emission inventories. Based on 19 billion trajectories, we show how big the emission difference could be using different approaches: 99% variation coefficients on regional total (including 31% emissions from non-local trucks), and ± as large as 15 times on individual counties. Even if total amounts are set the same, the emissions on primary cargo routes were underestimated in the former by a multiple of 2-10 using aggregated approaches. Time allocation proxies are generated, indicating the importance of day-to-day estimation because the variation reached 26-fold. Low emission zone policy reduced emissions in the zone, but raised emissions in upwind areas in Beijing's case. Comprehensive measures should be considered, e.g. the demand-side optimization.

Estimation of PM2.5 mortality burden in China with new exposure estimation and local concentration-response function.

The estimation of PM2.5-related mortality is becoming increasingly important. The accuracy of results is largely dependent on the selection of methods for PM2.5 exposure assessment and Concentration-Response (C-R) function. In this study, PM2.5 observed data from the China National Environmental Monitoring Center, satellite-derived estimation, widely collected geographic and socioeconomic information variables were applied to develop a national satellite-based Land Use Regression model and evaluate PM2.5 exposure concentrations within 2013-2015 with the resolution of 1 km × 1 km. Population weighted concentration declined from 72.52 µg/m3 in 2013 to 57.18 µg/m3 in 2015. C-R function is another important section of health effect assessment, but most previous studies used the Integrated Exposure Regression (IER) function which may currently underestimate the excess relative risk of exceeding the exposure range in China. A new Shape Constrained Health Impact Function (SCHIF) method, which was developed from a national cohort of 189,793 Chinese men, was adopted to estimate the PM2.5-related premature deaths in China. Results showed that 2.19 million (2013), 1.94 million (2014), 1.65 million (2015) premature deaths were attributed to PM2.5 long-term exposure, different from previous understanding around 1.1-1.7 million. The top three provinces of the highest premature deaths were Henan, Shandong, Sichuan, while the least ones were Tibet, Hainan, Qinghai. The proportions of premature deaths caused by specific diseases were 53.2% for stroke, 20.5% for ischemic heart disease, 16.8% for chronic obstructive pulmonary disease and 9.5% for lung cancer. IER function was also used to calculate PM2.5-related premature deaths with the same exposed level used in SCHIF method, and the comparison of results indicated that IER had made a much lower estimation with less annual amounts around 0.15-0.5 million premature deaths within 2013-2015.