Organic Emissions of Volatile Chemical Products in Canada: Emission Inventories, Indoor-to-Outdoor Transfer, and Regional Impacts.

The contribution of volatile chemical products (VCPs) to ambient air pollution has increased following decades of regulating combustion sources. There is a research gap concerning the impact of indoor physicochemical phenomena on VCP emissions. In this work, a bottom-up speciated VCP emission inventory with indoor-outdoor resolution was developed for Canada, an industrialized country with low air pollution levels, whose major cities are among the largest urban areas in North America. VCPs were estimated to account for about 290 kilotons of gaseous organic emissions for a typical year in the 2010s, with more than 60% of emissions occurring indoors. Coatings and cleaners were the most emissive VCP categories. Oxygenated species and saturated aliphatics dominated the chemical profiles of most emissions. Less than 5% of VCP emissions were impacted by indoor physicochemical phenomena. VCP emissions were predicted to account for 0.8-3.2 s-1 of OH reactivity and 0.22-0.52 µg/m3 of secondary organic aerosol formation potential in major urban areas in Canada. Our predictions aligned with previous measurements concerning indoor and outdoor organic pollutant levels, underscoring the important air quality impacts of VCPs relative to other sources. Our results provide helpful insights for future research regarding VCP emissions, especially from indoor spaces.

Direct identification of total and missing OH reactivities from light-duty gasoline vehicle exhaust in China based on LP-LIF measurement.

Considerable efforts have been devoted to characterising the chemical components of vehicle exhaust. However, these components may not accurately reflect the contribution of vehicle exhaust to atmospheric reactivity because of the presence of species not accounted for ("missing species") given the limitations of analytical instruments. In this study, we improved the laser photolysis-laser-induced fluorescence (LP-LIF) technique and applied it to directly measure the total OH reactivity (TOR) in exhaust gas from light-duty gasoline vehicles in China. The TOR for China I to VI-a vehicles was 15.6, 16.3, 8.4, 2.6, 1.5, and 1.6 × 104 sec-1, respectively, reflecting a notable drop as emission standards were upgraded. The TOR was comparable between cold and warm starts. The missing OH reactivity (MOR) values for China I to IV vehicles were close to zero with a cold start but were much higher with a warm start. The variations in oxygenated volatile organic compounds (OVOCs) under different emission standards and for the two start conditions were similar to those of the MOR, indicating that OVOCs and the missing species may have similar production processes. Online measurement revealed that the duration of the stable driving stage was the primary factor leading to the production of OVOCs and missing species. Our findings underscore the importance of direct measurement of TOR from vehicle exhaust and highlight the necessity of adding OVOCs and other organic reactive gases in future upgrades of emission standards, such that the vehicular contribution to atmospheric reactivity can be more effectively controlled.

Upgrading Emission Standards Inadvertently Increased OH Reactivity from Light-Duty Diesel Truck Exhaust in China: Evidence from Direct LP-LIF Measurement.

Vehicular exhaust is an important source of reactive gases responsible for the formation of ozone and secondary organic aerosols (SOAs) in the atmosphere. Although significant efforts have been made to characterize the chemical compounds associated with vehicular exhaust, there is still a wealth of compounds that are unable to be detected, posing uncertainties in estimating their contribution to atmospheric reactivity. In this study, by improving laser-induced fluorescence techniques, we achieved the first-ever direct measurement of the total OH reactivity (TOR) from light-duty diesel truck (LDDT) exhaust with different emission standards. We found that the TOR from the LDDT exhaust was 80-130 times the TOR from the gasoline exhaust measured in Japan. Unexpectedly, we discovered increased TOR emissions along with upgrading emission standards, possibly as a collective result of high combustion temperature in the engine and the oxidation catalysts in the exhaust after-treatment that favor production of highly oxidized organics in the stricter emission standard. Most of these oxidized organics are unable to be speciated by routine measurements, resulting in the missing OH reactivity increasing rapidly from 1.91% for China III to 42.0% for China V LDDT. Upgrading the emission standard failed to reduce the TOR from LDDT exhaust, which may inadvertently promote the contribution of LDDT to the formation of ozone and SOA pollution in China.

Contrasting Reactive Organic Carbon Observations in the Southeast United States (SOAS) and Southern California (CalNex).

Despite the central role of reactive organic carbon (ROC) in the formation of secondary species that impact global air quality and climate, our assessment of ROC abundance and impacts is challenged by the diversity of species that contribute to it. We revisit measurements of ROC species made during two field campaigns in the United States: the 2013 SOAS campaign in forested Centreville, AL, and the 2010 CalNex campaign in urban Pasadena, CA. We find that average measured ROC concentrations are about twice as high in Pasadena (73.8 µgCsm-3) than in Centreville (36.5 µgCsm-3). However, the OH reactivity (OHR) measured at these sites is similar (20.1 and 19.3 s-1). The shortfall in OHR when summing up measured contributions is 31%, at Pasadena and 14% at Centreville, suggesting that there may be a larger reservoir of unmeasured ROC at the former site. Estimated O3 production and SOA potential (defined as concentration × yield) are both higher during CalNex than SOAS. This analysis suggests that the ROC in urban California is less reactive, but due to higher concentrations of oxides of nitrogen and hydroxyl radicals, is more efficient in terms of O3 and SOA production, than in the forested southeastern U.S.

The Indoor Chemical Human Emissions and Reactivity (ICHEAR) project: Overview of experimental methodology and preliminary results.

With the gradual reduction of emissions from building products, emissions from human occupants become more dominant indoors. The impact of human emissions on indoor air quality is inadequately understood. The aim of the Indoor Chemical Human Emissions and Reactivity (ICHEAR) project was to examine the impact on indoor air chemistry of whole-body, exhaled, and dermally emitted human bioeffluents under different conditions comprising human factors (t-shirts/shorts vs long-sleeve shirts/pants; age: teenagers, young adults, and seniors) and a variety of environmental factors (moderate vs high air temperature; low vs high relative humidity; presence vs absence of ozone). A series of human subject experiments were performed in a well-controlled stainless steel climate chamber. State-of-the-art measurement technologies were used to quantify the volatile organic compounds emitted by humans and their total OH reactivity; ammonia, nanoparticle, fluorescent biological aerosol particle (FBAP), and microbial emissions; and skin surface chemistry. This paper presents the design of the project, its methodologies, and preliminary results, comparing identical measurements performed with five groups, each composed of 4 volunteers (2 males and 2 females). The volunteers wore identical laundered new clothes and were asked to use the same set of fragrance-free personal care products. They occupied the ozone-free (<2 ppb) chamber for 3 hours (morning) and then left for a 10-min lunch break. Ozone (target concentration in occupied chamber ~35 ppb) was introduced 10 minutes after the volunteers returned to the chamber, and the measurements continued for another 2.5 hours. Under a given ozone condition, relatively small differences were observed in the steady-state concentrations of geranyl acetone, 6MHO, and 4OPA between the five groups. Larger variability was observed for acetone and isoprene. The absence or presence of ozone significantly influenced the steady-state concentrations of acetone, geranyl acetone, 6MHO, and 4OPA. Results of replicate experiments demonstrate the robustness of the experiments. Higher repeatability was achieved for dermally emitted compounds and their reaction products than for constituents of exhaled breath.

[Compositional Characteristics of Volatile Organic Compounds in Typical Industrial Areas of the Pearl River Delta: Importance of Oxygenated Volatile Organic Compounds].

Volatile organic compounds (VOCs) are key components of tropospheric chemistry, of which industrial emissions are an important source of atmospheric VOCs. In this study, online measurements of 74 VOCs were made in a typical industrial area of the Pearl River Delta in southern China during the early summer of 2021. The mean volume mixing ratio of total volatile organic compounds (TVOC) was (81.9±45.4)×10-9 during the campaign. Among them, oxygenated volatile organic compounds (OVOCs) accounted for the largest fraction of TVOC, with an average of 51.5%, followed by aromatics, accounting for 19.4% of TVOC. The proportion of OVOCs in TVOC gradually increased with the increase in TVOC concentration. Industry-related emissions were the main contributors to aromatics and OVOCs in this region. Aromatics and OVOCs were the two major contributors to the ozone formation potential (OFP), accounting for 56.4% and 26.7%, respectively. Furthermore, OVOCs also contributed 40.0% of the total ·OH reactivity from VOCs. Xylenes, toluene, acrolein, and ethyl acetate had a greater contribution to the formation of secondary pollution; thus, these species should be given priority for controlling secondary pollution. Our results underscore the severity of OVOCs pollution in industrial areas and the important roles of OVOCs in secondary pollution.

Chemical reactivity of volatile organic compounds and their effects on ozone formation in a petrochemical industrial area of Lanzhou, Western China.

Measurements of ozone (O3) and its precursors were performed in the summer of 2019 in Lanzhou, a petrochemical industrial city, to better understand the reactivity of volatile organic compounds (VOCs) and their effects on O3 production. During the campaign, the daily maximum 8-hour average (MDA8) O3, NO2, and total VOC (TVOC) concentrations reached 72.2 ± 19.9 ppb, 24.9 ± 10.8 ppb, and 50.8 ± 46.1 ppb, respectively. Alkanes, alkenes, halocarbons, aromatics, and alkynes contributed 45.3%, 24.0%, 16.5%, 10.0%, and 4.2% to TVOCs, respectively. The OH reactivity and relative incremental reactivity (RIR) of VOCs at different times were calculated. The results indicated that alkenes played a predominant role, accounting for an average of 68.5% of the initial VOC reactivity. Compared to other regions, alkenes are relatively more important for O3 formation in the petrochemical industry area of Lanzhou, while aromatics are relatively less important. Generally, O3 formation occurred in a VOC-limited regime in the morning and in a transitional regime in the afternoon. The response surface methodology (RSM) combined with a chemical box model was applied to obtain relationships between O3 and its precursors and determine the most effective way to reduce the O3 concentration. Reduction in the non-alkene concentration slightly affected the O3 concentration. In contrast, the effect of nitrogen oxides (NOx) was closely related to the alkene concentration, and NOx concentration reduction could lead to an increase in the O3 concentration when alkenes were abated to less than 80% of the present concentration. To mitigate O3 pollution near the petrochemical industrial area of Lanzhou, reducing the alkene concentration, especially the C4 alkene concentration (1,3-butadiene, cis-2-butene, and trans-2-butene), was the fastest and most effective control strategy. The results of this study serve as a reference for O3 pollution control in petrochemical industrial areas.

Quantification of temperature dependence of vehicle evaporative volatile organic compound emissions from different fuel types in China.

The evaporative emissions of volatile organic compounds (VOCs) from motor vehicles are dependent upon the ambient temperature. However, the quantitative relationship between evaporative VOC emissions and ambient temperature has rarely been reported, and it is not reflected in the Chinese VOCs emission inventory (EI). In this study, a series of evaporative tests were conducted on a parked gasoline-fueled vehicle in a Variable Temperature Sealed Housing Evaporative Determination chamber under seven temperatures from 298 K to 313 K at intervals of 2.5 K. Results showed that total hydrocarbon emissions at 313 K were 25.7, 12.3, and 26.7 times those at 298 K for China V, China VI, and ethanol-blended E10 fuels, respectively. China V consistently exhibited the lowest evaporative VOC emissions at all temperatures, while those of E10 surpassed even those of China VI and became the highest at 308 K and higher. Along with increasing temperature, the proportions of alkanes and alkenes gradually increased whereas those of aromatics and oxygenated VOCs decreased. Alkenes accounted for less than 20% of the evaporative VOC emissions but contributed to approximately 60% of the total OH loss (LOH) at 298 K and to over 70% at 313 K. cis-2-Butene and trans-2-butene were responsible for the greatest increase in LOH from China V, due to their higher OH reactivity. Our results clearly demonstrated the exponential increases of evaporative VOC emissions and the associated atmospheric reactivity with temperature, and also highlighted that upgrading the emission standard from China V to China IV and promoting the E10 fuel would not contribute to the reduction of evaporative VOC emissions. The strong temperature dependence of evaporative VOC emissions underscores the importance of developing a temperature-driven dynamic EI in China, and the functional relationships retrieved from this study form an essential step in developing such a dynamic EI.

Season-wise analyses of VOCs, hydroxyl radicals and ozone formation chemistry over north-west India reveal isoprene and acetaldehyde as the most potent ozone precursors throughout the year.

The north-west Indo-Gangetic Plain is the agricultural cereal-basket of India owing to its prolific wheat and rice production. Surface ozone pollution is of growing concern over it, yet no detailed year-round in-situ measurements of its most reactive precursors, particularly the volatile organic compounds (VOCs) are available from this region. Here, using the first year-long continuous measurements of 23 major VOCs, ozone, NOx, CO and their atmospheric oxidation products from a regionally representative site in north-west India, we evaluated speciated OH reactivities (OHR), ozone formation potential (OFP) and ozone production regimes (OPR) across all seasons. The average seasonal OHR ranged from 14 s-1 (winter) to 21.5 s-1 (summer). We provide the first estimate of OH radical mixing ratios varying between 0.06 and 0.37 ppt in different seasons for the peak daytime hours in this region. Recycling via HO2+NO was the most important pathway contributing to >85% of the OH production throughout the year. Contrary to satellite derived proxies and chemical transport models which predict NOx sensitive OPR, we show it to be strongly sensitive to both VOCs and NOx (>90% days in a year). Remarkably for densely populated regions, isoprene and acetaldehyde collectively accounted for ~30-50% of the total OFP in all seasons. Biogenic emissions of isoprene (reaching 12.9 mg/m2/h) and high acetaldehyde from anthropogenic and photochemical sources were observed for all seasons. Monitoring and control of isoprene and acetaldehyde are therefore urgently required for efforts focused on mitigating surface ozone pollution in this demographically important region of the world.

Parameterized atmospheric oxidation capacity and speciated OH reactivity over a suburban site in the North China Plain: A comparative study between summer and winter.

The atmospheric oxidation capacity (AOC) and photochemical reactivity are of increasing concern owing to their roles in photochemical pollution. The AOC and OH reactivity were evaluated based on simultaneous measurements of volatile organic compounds (VOCs), trace gases and photolysis frequency during summer and winter campaigns at a suburban site in Xianghe. The AOC exhibited well-defined seasonal and diurnal patterns, with higher intensities during the summertime and daytime than during the wintertime and nighttime, respectively. The major reductants contributing to the AOC during the summertime were CO (41%) and alkenes (41%), whereas CO (40%) and oxygenated VOCs (OVOCs) (30%) dominated the AOC during the wintertime. The dominant oxidant contributor to the AOC during the daytime was OH (≥93%), while the contributions of O3 and NO3 (≥75%) to the AOC increased during the nighttime. High values during the wintertime and an increase at night were features of the speciated OH reactivity. Inorganic compounds (NOx and CO) dominated the speciated OH reactivity (76% and 85% during the summer and winter campaigns, respectively). Among VOCs, the dominant contributors were alkenes (12%) and OVOCs (7%) during the summer and winter campaigns, respectively. The ratio of NOx- and VOC-attributed OH reactivity indicated that O3 formation occurred under a VOC-limited regime during the summertime and that aromatics had the largest potential to form O3. Isoprene and m/p-xylene were the most important contributors to the AOC, OH reactivity and O3-forming among VOCs during the summertime, biogenic sources and secondary formation and industrial production were the main sources of these species. During the wintertime, hexanal and ethylene were the key VOC species contributing to the AOC and OH reactivity, and solvent usage and traffic-related emissions were the main contributing sources. We recommend that priority measures for the control of VOC species and sources should be taken when suitable. CAPSULE: This study focused on the similarities and differences in the AOC and speciated OH reactivity during summer and winter campaigns.

Significant decreases in the volatile organic compound concentration, atmospheric oxidation capacity and photochemical reactivity during the National Day holiday over a suburban site in the North China Plain.

To what extent anthropogenic emissions could influence volatile organic compound (VOCs) concentrations and related atmospheric reactivity is still poorly understood. China's 70th National Day holidays, during which anthropogenic emissions were significantly reduced to ensure good air quality on Anniversary Day, provides a unique opportunity to investigate these processes. Atmospheric oxidation capacity (AOC), OH reactivity, secondary transformation, O3 formation and VOCs-PM2.5 sensitivity are evaluated based on parameterization methods and simultaneous measurements of VOCs, O3, NOx, CO, SO2, PM2.5, JO1D, JNO2, JNO3 carried out at a suburban site between Beijing and Tianjin before, during, and after the National Day holiday 2019. During the National Day holidays, the AOC, OH reactivity, O3 formation potential (OFP) and secondary organic aerosol formation potential (SOAP) were 1.6 × 107 molecules cm-3 s-1, 41.8 s-1, 299.2 µg cm-3 and 1471.8 µg cm-3, respectively, which were 42%, 29%, 47% and 42% lower than pre-National Day values and -12%, 42%, 36% and 42% lower than post-National Day values, respectively. Reactions involving OH radicals dominated the AOC during the day, but OH radicals and O3 reactions at night. Alkanes (the degree of unsaturation = 0, (D, Equation (1)) accounted for the largest contributions to the total VOCs concentration, oxygenated VOCs (OVOCs; D ≤ 1) to OH reactivity and OFP, and aromatics (D = 4) to the SOAP. O3 production was identified as VOCs-limited by VOCs (ppbC)/NOx (ppbv) ratios during the sampling campaign, with greater VOCs limitation during post- National Day and more-aged air masses during the National Day. The VOCs-sensitivity coefficient (VOCs-S) suggested that VOCs were more sensitive to PM2.5 in low-pollution domains and during the National Day holiday. This study emphasizes the importance of not only the abundance, reactivity, and secondary transformation of VOCs but also the effects of VOCs on PM2.5 for the development of effective control strategies to minimize O3 and PM2.5 pollution.

Total hydroxyl radical reactivity measurements in a suburban area during AQUAS-Tsukuba campaign in 2017.

Missing hydroxyl radical (OH) reactivity from unknown/unmeasured trace species empirically accounts for 10%-30% of total OH reactivity and may cause significant uncertainty regarding estimation of photochemical ozone production. Thus, it is essential to unveil the missing OH reactivity for developing an effective ozone mitigation strategy. In this study, we conducted simultaneous observations of total OH reactivity and 54 reactive trace species in a suburban area as part of the Air QUAlity Study (AQUAS)-Tsukuba campaign for the summer of 2017 to gain in-depth insight into total OH reactivity in an area that experienced relatively high contributions of secondary pollutants. The campaign identified on average 35.3% of missing OH reactivity among total OH reactivity (12.9 s-1). In general, ozone-production potential estimation categorized ozone formation in this area as volatile organic compound (VOC)-limited conditions, and missing OH reactivity may increase ozone production potential 40% on average if considered. Our results suggest the importance of photochemical processes of both AVOCs and BVOCs for the production of missing OH reactivity and that we may underestimate the importance of reducing precursors in approach to suppressing ozone production if we ignore the contribution of their photochemical products.

Oxidizing capacity of the rural atmosphere in Hong Kong, Southern China.

Atmospheric oxidizing capacity (AOC), dominated by the hydroxyl radical (OH), is an important index of the self-cleaning capacity of atmosphere and plays a vital role in the tropospheric chemistry. To better understand the key processes governing the chemistry of rural atmosphere of southern China, we analyzed the oxidation capacity and radical chemistry at a regional background site in Hong Kong from 23 August to 22 December 2012, which covered the summer, autumn and winter seasons. A chemical box model built on the latest Master Chemical Mechanism (v3.3) was used to elucidate the OH reactivity and sources of ROX radicals (ROX=OH+HO2+RO2). The AOC showed a clear seasonal pattern with stronger intensity in late summer compared to autumn and winter. Reactions with NO2 (30%) and oxygenated volatile organic compounds (OVOCs) (31%) together dominated the OH loss in summer, while reactions with CO (38% in autumn and 39% in winter) and OVOCs (34% in autumn and 25% in winter) made larger contributions in autumn and winter. Photolysis of O3 (36%-47%) presented the major ROX source during all three seasons. The second largest ROx source was HONO photolysis (25%) in summer compared to HCHO photolysis in autumn (20%) and winter (21%). Besides, photolysis of other OVOCs was another important primary source of ROx radicals with average contributions of 14%, 13% and 20% for the summer, autumn and winter cases, respectively. Overall, the present study evaluates the oxidizing capacity of the rural atmosphere of South China and elucidates the varying characteristics of photochemical processes in different air masses.

Sources of C2-C4 alkenes, the most important ozone nonmethane hydrocarbon precursors in the Pearl River Delta region.

Surface ozone is becoming an increasing concern in China's megacities such as the urban centers located in the highly industrialized and densely populated Pearl River Delta (PRD) region, where previous studies suggested that ozone production is sensitive to VOC emissions with alkenes being important precursors. However, little was known about sources of alkenes. Here we present our monitoring of ambient volatile organic compounds at four representative urban, suburban and rural sites in the PRD region during November-December 2009, which experienced frequent ozone episodes. C2-C4 alkenes, whose total mixing ratios were 11-20% of non-methane hydrocarbons (NMHCs) quantified, accounted for 38-64% of ozone formation potentials (OFPs) and 30-50% of the total hydroxyl radical (OH) reactivity by NMHCs. Ethylene was the most abundant alkene, accounting for 8-15% in total mixing ratios of NMHCs and contributed 25-46% of OFPs. Correlations between C2-C4 alkenes and typical source tracers suggested that ethylene might be largely related to vehicle exhausts and industry activities, while propene and butenes were much more LPG-related. Positive Matrix Factorization (PMF) confirmed that vehicle exhaust and liquefied petroleum gas (LPG) were two major sources that altogether accounted for 52-62%, 58-77%, 73-83%, 68-79% and 73-84% for ethylene, propene, 1-butene, trans-2-butene and cis-2-butene, respectively. Vehicle exhausts alone contributed 32-49% ethylene and 35-41% propene. Industry activities contributed 13-23% ethylene and 7-20% propene. LPG instead contributed the most to butenes (38-65%) and substantially to propene (23-36%). Extensive tests confirmed high fractions of propene and butenes in LPG then used in Guangzhou and in LPG combustion plumes; therefore, limiting alkene contents in LPG would benefit regional ozone control.