Volatile chemical products emerging as largest petrochemical source of urban organic emissions.

Volatile organic compound (VOC) emissions to the atmosphere cause air pollution associated with adverse health outcomes. Volatile chemical products (VCPs) have emerged as a VOC emission category that is poorly characterized by air pollution models. VCPs are present throughout developed economies in manufactured products that include paints, cleaning agents, printing inks, adhesives and pesticides. Air quality models must accurately represent the atmospheric chemistry of VCPs to develop reliable air quality plans. We develop a chemical mechanism for oxidant formation by VCP compounds that is compatible with version 6 of the Carbon Bond (CB6) mechanism. We analyzed a recent U.S. VCP emission inventory and found that ~67% of the emissions mass can be well-represented by existing CB6 mechanism species but ~33% could be better represented by adding 16 emitted VCP species including alcohols, ethers, esters, alkanes and siloxanes. For larger alkanes, an important VCP category, our mechanism explicitly represents temperature-dependent organic nitrate formation and autoxidation via 1,6 H-shift reactions consistent with current knowledge. We characterized the ozone forming potential of each added VCP species and compared it to the current practice of representing VCP species by surrogate species. Nine of the sixteen added VCP species are less reactive than the current practice, namely i-propanol, dimethyl ether, methyl formate, ethyl formate, methyl acetate, larger esters, i-butane, large alkanes and siloxanes. These less reactive VCP species are characterized by having OH-reactions that form un-reactive products. A total of 7 of the 16 VCP species are more reactive than current practice, namely n-propanol, ethylene glycol, propylene glycol, larger alcohols, diethyl ether, larger ethers and ethyl acetate. These more reactive VCP species are characterized as containing functional groups that promote faster OH-reaction. The VCP chemical mechanism for CB6 can improve how VCP impacts to oxidants are represented and will be incorporated to CB7. Changes in oxidant formation resulting from the mechanism update will depend on how VCP emissions are speciated for modeling, which is uncertain, and impacts may go in opposite directions for specific categories of VCP emissions that have unique chemical speciation characteristics. We provide guidance to help modelers implement the VCP mechanism update.

Estimation of Anthropogenic VOCs Emission Based on Volatile Chemical Products: A Canadian Perspective.

Despite decades of declining air pollution, urban U.S. areas are still affected by summertime ozone and wintertime particulate matter exceedance events. Volatile organic compounds (VOCs) are known precursors of secondary organic aerosol (SOA) and photochemically produced ozone. Urban VOC emission sources, including on-road transportation emissions, have decreased significantly over the past few decades through successful regulatory measures. These drastic reductions in VOC emissions have led to a change in the distribution of urban emissions and noncombustion sources of VOCs such as those from volatile chemical products (VCPs), which now account for a higher fraction of the urban VOC burden. Given this shift in emission sources, it is essential to quantify the relative contribution of VCP and mobile source emissions to urban pollution. Herein, ground site and mobile laboratory measurements of VOCs were performed. Two ground site locations with different population densities, Boulder, CO, and New York City (NYC), NY, were chosen in order to evaluate the influence of VCPs in cities with varying mixtures of VCPs and mobile source emissions. Positive matrix factorization was used to attribute hundreds of compounds to mobile- and VCP-dominated sources. VCP-dominated emissions contributed to 42 and 78% of anthropogenic VOC emissions for Boulder and NYC, respectively, while mobile source emissions contributed 58 and 22%. Apportioned VOC emissions were compared to those estimated from the Fuel-based Inventory of Vehicle Emissions and VCPs and agreed to within 25% for the bulk comparison and within 30% for more than half of individual compounds. The evaluated inventory was extended to other U.S. cities and it suggests that 50 to 80% of emissions, reactivity, and the SOA-forming potential of urban anthropogenic VOCs are associated with VCP-dominated sources, demonstrating their important role in urban U.S. air quality.

Decades of air quality improvements have substantially reduced the motor vehicle emissions of volatile organic compounds (VOCs). Today, volatile chemical products (VCPs) are responsible for half of the petrochemical VOCs emitted in major urban areas. We show that VCP emissions are ubiquitous in US and European cities and scale with population density. We report significant VCP emissions for New York City (NYC), including a monoterpene flux of 14.7 to 24.4 kg ⋅ d-1 ⋅ km-2 from fragranced VCPs and other anthropogenic sources, which is comparable to that of a summertime forest. Photochemical modeling of an extreme heat event, with ozone well in excess of US standards, illustrates the significant impact of VCPs on air quality. In the most populated regions of NYC, ozone was sensitive to anthropogenic VOCs (AVOCs), even in the presence of biogenic sources. Within this VOC-sensitive regime, AVOCs contributed upwards of ∼20 ppb to maximum 8-h average ozone. VCPs accounted for more than 50% of this total AVOC contribution. Emissions from fragranced VCPs, including personal care and cleaning products, account for at least 50% of the ozone attributed to VCPs. We show that model simulations of ozone depend foremost on the magnitude of VCP emissions and that the addition of oxygenated VCP chemistry impacts simulations of key atmospheric oxidation products. NYC is a case study for developed megacities, and the impacts of VCPs on local ozone are likely similar for other major urban regions across North America or Europe.

Abstract. Volatile organic compounds (VOCs) are key precursors of ozone and particulate matter, which are the two dominant air pollutants in urban environments. However, compositions and sources of VOCs in urban air aloft have rarely been reported so far. To address this matter, highly time-resolved measurements of VOCs were made by a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a 450 m platform on the Canton Tower in Guangzhou, China. A combination of in situ measurements and modeling techniques was used to characterize variations in and sources of VOCs. Five sources were identified from positive matrix factorization (PMF) analysis, namely daytime mixed (e.g., biogenic emissions and secondary formation), visitor-related (e.g., human breath, cooking, and volatilization of ethanol-containing products), vehicular–industrial, regional transport, and volatile chemical product (VCP) (i.e., volatilization of personal care products), contributing on average to 21 %, 30 %, 28 %, 10 %, and 11 % of total VOC (TVOC) mixing ratios, respectively. We observe that contributions of the visitor-related source, mainly composed of ethanol, followed with the variation in visitor numbers on the tower well. The VCP-dominated source only had an average contribution of ∼5.7 ppb during the campaign, accounting for a small fraction (11 %) of TVOC mixing ratios but a large fraction (22 %) of the total OH reactivity. However, large fractions of reactive VOC species, e.g., monoterpenes (49 %), were attributed to the VCP-dominated source, indicating important contributions of VCPs to ambient concentrations of these species in urban environments. Vertical profiles of air pollutants (namely NOx, ozone, Ox, and PM2.5), measured at 5, 118, 168, and 488 m, exhibited more evident gradients at night than in the daytime owing to the stronger stability of the nocturnal boundary layer. Mixing ratios of VOC species during the nighttime generally decreased with time when the 450 m platform was located in the nocturnal residual layer and markedly increased when impacted by emissions at ground level. The results in this study demonstrated composition characteristics and sources of VOCs in urban air aloft, which could provide valuable implications in making strategies for control of VOCs and secondary air pollutants.

With traffic emissions of volatile organic compounds (VOCs) decreasing rapidly over the last decades, the contributions of the emissions from other source categories, such as volatile chemical products (VCPs), have become more apparent in urban air. In this work, in situ measurements of various VOCs are reported for New York City, Pittsburgh, Chicago, and Denver. The magnitude of different emission sources relative to traffic is determined by measuring the urban enhancement of individual compounds relative to the enhancement of benzene, a known tracer of fossil fuel in the United States. The enhancement ratios of several VCP compounds to benzene correlate well with population density (R2 ∼ 0.6-0.8). These observations are consistent with the expectation that some human activity should correlate better with the population density than transportation emissions, due to the lower per capita rate of driving in denser cities. Using these data, together with a bottom-up fuel-based inventory of vehicle emissions and volatile chemical products (FIVE-VCP) inventory, we identify tracer compounds for different VCP categories: decamethylcyclopentasiloxane (D5-siloxane) for personal care products, monoterpenes for fragrances, p-dichlorobenzene for insecticides, D4-siloxane for adhesives, para-chlorobenzotrifluoride (PCBTF) for solvent-based coatings, and Texanol for water-based coatings. Furthermore, several other compounds are identified (e.g., ethanol) that correlate with population density and originate from multiple VCP sources. Ethanol and fragrances are among the most abundant and reactive VOCs associated with VCP emissions.

Emerging sources, such as volatile chemical products (VCPs) and other non-traditional emission categories, are becoming increasingly important in urban air pollution as the contributions of recognized sources such as traffic and industrial emissions decline. Indoor emissions constitute a large fraction of organic gaseous species from these sources, making buildings potential contributors to ambient air pollution. This study illustrates building emissions by presenting findings from a sampling campaign in downtown Toronto, analyzing volatile organic compounds (VOCs) from the mechanical ventilation inlet and exhaust air streams of a multi-unit residential building (110 units). Due to indoor emissions, VOCs were detected more frequently and at higher concentrations (median levels higher by about 22%) in the exhaust stream than in the inlet stream, indicating that the building serves as a net VOC source to the ambient air. VCP-related species were consistently more abundant in the exhaust air, confirming the influence of indoor sources. In particular, median concentrations of volatile methyl siloxanes and monoterpenoids associated with emissions from adhesives, personal care products, and cleaning agents ranged from about 2-5 μg m-3 in the exhaust stream in comparison with 0.2-0.5 μg m-3 within the inlet stream. Source apportionment analysis of VOC concentrations across the exhaust and inlet airstreams revealed indoor emissions of siloxanes, monoterpenoids, and oxygenated VOCs from coatings, cleaners, and personal care products as primary contributors to exhaust stream trends. Net building VOC emissions, defined as the rate of outflowing minus the inflowing VOCs, were calculated from the measured concentrations and ventilation rates. The resulting values aligned with indoor emissions predicted from a published VCP emission inventory for Canada, emphasizing the pivotal impact of VCP indoor sources on urban air quality. Exhaust and inlet stream concentrations of VCP-related species were found to be significantly (p < 0.05) correlated, suggesting the building emissions influencing outdoor VOC levels. These results highlight the crucial impact of indoor emissions, especially from VCPs, on ambient air quality and the need for further research into indoor-to-outdoor pollutant transfer mechanisms to address urban air pollution.

Volatile organic compounds (VOCs) are key precursors of ozone and particulate matter that are the two dominant air pollutants in urban environments. However, compositions and sources of VOCs in urban air aloft were rarely reported by far. To address this matter, highly time-resolved measurements of VOCs were made by proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a 450-m platform on the Canton Tower in Guangzhou, China. A combination of in-situ measurements and modeling techniques was used to characterize variations and sources of VOCs. Five sources were identified from positive matrix factorization (PMF) analysis, namely daytime-mixed (e.g., biogenic emissions and secondary formation), visitor-related (e.g., human breath and volatilization of ethanol-containing products), vehicular+industrial, regional transport, and volatile chemical product (VCP)-dominated (i.e., volatilization of personal care products), contributing on average to 22 %, 30 %, 28 %, 10 %, and 11 % of total VOC (TVOC) mixing ratios, respectively. We observe that contributions of the visitor-related source, mainly composed of ethanol, followed well with the variation patterns of visitor number on the tower. The VCP-dominated source only had an average contribution of ~5.7 ppb during the campaign, accounting for a small fraction (11 %) of TVOC mixing ratios. However, large fractions of some VOC species, e.g., monoterpenes (49 %), were attributed to the VCP-dominated source, indicating significant contributions of VCPs to ambient concentrations of these species in urban environments. Vertical profiles of air pollutants (including NOx, ozone, Ox, and PM2.5), measured at 5 m, 118 m, 168 m, and 488 m, exhibited more evident gradients at night than in the daytime owing to stronger stability of the nocturnal boundary layer. Mixing ratios of VOC species during the nighttime generally decreased with time when the 450-m platform was located in the nocturnal residual layer and significantly increased when impacted by emissions at ground. The results in this study demonstrated composition characteristics and sources of VOCs in urban air aloft, which could provide valuable implications in making control strategies of VOCs and secondary air pollutants.

Volatile organic compounds (VOCs) are key precursors of ozone and particulate matter that are the two dominant air pollutants in urban environments. However, compositions and sources of VOCs in urban air aloft were rarely reported by far. To address this matter, highly time-resolved measurements of VOCs were made by proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a 450-m platform on the Canton Tower in Guangzhou, China. A combination of in-situ measurements and modeling techniques was used to characterize variations and sources of VOCs. Five sources were identified from positive matrix factorization (PMF) analysis, namely daytime-mixed (e.g., biogenic emissions and secondary formation), visitor-related (e.g., human breath and volatilization of ethanol-containing products), vehicular+industrial, regional transport, and volatile chemical product (VCP)-dominated (i.e., volatilization of personal care products), contributing on average to 22 %, 30 %, 28 %, 10 %, and 11 % of total VOC (TVOC) mixing ratios, respectively. We observe that contributions of the visitor-related source, mainly composed of ethanol, followed well with the variation patterns of visitor number on the tower. The VCP-dominated source only had an average contribution of ~5.7 ppb during the campaign, accounting for a small fraction (11 %) of TVOC mixing ratios. However, large fractions of some VOC species, e.g., monoterpenes (49 %), were attributed to the VCP-dominated source, indicating significant contributions of VCPs to ambient concentrations of these species in urban environments. Vertical profiles of air pollutants (including NOx, ozone, Ox, and PM2.5), measured at 5 m, 118 m, 168 m, and 488 m, exhibited more evident gradients at night than in the daytime owing to stronger stability of the nocturnal boundary layer. Mixing ratios of VOC species during the nighttime generally decreased with time when the 450-m platform was located in the nocturnal residual layer and significantly increased when impacted by emissions at ground. The results in this study demonstrated composition characteristics and sources of VOCs in urban air aloft, which could provide valuable implications in making control strategies of VOCs and secondary air pollutants.

<strong class="journal-contentHeaderColor">Abstract.</strong> Volatile organic compounds (VOCs) are key precursors of ozone and particulate matter, which are the two dominant air pollutants in urban environments. However, compositions and sources of VOCs in urban air aloft have rarely been reported so far. To address this matter, highly time-resolved measurements of VOCs were made by a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a 450 m platform on the Canton Tower in Guangzhou, China. A combination of in situ measurements and modeling techniques was used to characterize variations in and sources of VOCs. Five sources were identified from positive matrix factorization (PMF) analysis, namely daytime mixed (e.g., biogenic emissions and secondary formation), visitor-related (e.g., human breath, cooking, and volatilization of ethanol-containing products), vehicular–industrial, regional transport, and volatile chemical product (VCP) (i.e., volatilization of personal care products), contributing on average to 21 %, 30 %, 28 %, 10 %, and 11 % of total VOC (TVOC) mixing ratios, respectively. We observe that contributions of the visitor-related source, mainly composed of ethanol, followed with the variation in visitor numbers on the tower well. The VCP-dominated source only had an average contribution of <span class="inline-formula">∼5.7</span> ppb during the campaign, accounting for a small fraction (11 %) of TVOC mixing ratios but a large fraction (22 %) of the total OH reactivity. However, large fractions of reactive VOC species, e.g., monoterpenes (49 %), were attributed to the VCP-dominated source, indicating important contributions of VCPs to ambient concentrations of these species in urban environments. Vertical profiles of air pollutants (namely <span class="inline-formula">NO_<i>x</i></span>, ozone, <span class="inline-formula">O_<i>x</i></span>, and PM<span class="inline-formula">_2.5</span>), measured at 5, 118, 168, and 488 m, exhibited more evident gradients at night than in the daytime owing to the stronger stability of the nocturnal boundary layer. Mixing ratios of VOC species during the nighttime generally decreased with time when the 450 m platform was located in the nocturnal residual layer and markedly increased when impacted by emissions at ground level. The results in this study demonstrated composition characteristics and sources of VOCs in urban air aloft, which could provide valuable implications in making strategies for control of VOCs and secondary air pollutants.

Volatile organic compounds (VOCs) are key precursors of ozone and particulate matter that are the two dominant air pollutants in urban environments. However, compositions and sources of VOCs in urban air aloft were rarely reported by far. To address this matter, highly time-resolved measurements of VOCs were made by proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) at a 450-m platform on the Canton Tower in Guangzhou, China. A combination of in-situ measurements and modeling techniques was used to characterize variations and sources of VOCs. Five sources were identified from positive matrix factorization (PMF) analysis, namely daytime-mixed (e.g., biogenic emissions and secondary formation), visitor-related (e.g., human breath and volatilization of ethanol-containing products), vehicular+industrial, regional transport, and volatile chemical product (VCP)-dominated (i.e., volatilization of personal care products), contributing on average to 22 %, 30 %, 28 %, 10 %, and 11 % of total VOC (TVOC) mixing ratios, respectively. We observe that contributions of the visitor-related source, mainly composed of ethanol, followed well with the variation patterns of visitor number on the tower. The VCP-dominated source only had an average contribution of ~5.7 ppb during the campaign, accounting for a small fraction (11 %) of TVOC mixing ratios. However, large fractions of some VOC species, e.g., monoterpenes (49 %), were attributed to the VCP-dominated source, indicating significant contributions of VCPs to ambient concentrations of these species in urban environments. Vertical profiles of air pollutants (including NOx, ozone, Ox, and PM2.5), measured at 5 m, 118 m, 168 m, and 488 m, exhibited more evident gradients at night than in the daytime owing to stronger stability of the nocturnal boundary layer. Mixing ratios of VOC species during the nighttime generally decreased with time when the 450-m platform was located in the nocturnal residual layer and significantly increased when impacted by emissions at ground. The results in this study demonstrated composition characteristics and sources of VOCs in urban air aloft, which could provide valuable implications in making control strategies of VOCs and secondary air pollutants.

Las Vegas, Nevada is an urban center in the southwest US where the population is rapidly growing. In Las Vegas, surrounded by the Mojave Desert, biogenic emissions are low, but anthropogenic emissions, especially along the Las Vegas Strip, are a large source of volatile organic compounds (VOC) and nitrogen oxides (NO + NO2 = NOx) from volatile chemical products, cooking, and fossil fuel usage. This makes Las Vegas an ideal place to study anthropogenic VOC emissions and oxidation in the absence of a strong biogenic signal. The urban air quality in Las Vegas was measured at a stationary site and with a mobile laboratory. Biogenic VOC influence, VOC enhancement ratios, and weekday‐weekend effects were evaluated. An Eulerian box model was constructed to evaluate the chemical processes impacting air quality in Las Vegas. The model showed that the daily ozone (O3) enhancement, taken as the maximum O3 produced midday above background, was approximately 30 ppb. The O3 sensitivities to VOCs and NOx showed that reductions in both would reduce O3 production. Reducing NOx or VOCs by half would reduce O3 by 10.5 and 11.5 ppb, respectively. Reducing both NOx and VOCs together would decrease O3 by 15 ppb. The O3 contribution from biogenic VOCs was ∼3.5 ppb, which is about 10% of the total produced O3. This differs from other regions of the US, such as New York or Los Angeles, where biogenic VOCs contribute significantly to urban ozone.

The declining trend in vehicle emissions has underscored the growing significance of Volatile Organic Compound (VOC) emissions from Volatile Chemical Products (VCP). However, accurately representing VOC chemistry in simplified chemical mechanisms remains challenging due to its chemical complexity including speciation and reactivity. Previous studies have predominantly focused on VOCs from fossil fuel sources, leading to an underrepresentation of VOC chemistry from VCP sources. We developed an integrated chemical mechanism, RACM2B-VCP, that is compatible with WRF-Chem and is aimed to enhance the representation of VOC chemistry, particularly from VCP sources, within the present urban environment. Evaluation against the Air Quality System (AQS) network data demonstrates that our model configured with RACM2B-VCP reproduces both the magnitude and spatial variability of O3 as well as PM2.5 in Los Angeles. Furthermore, evaluation against comprehensive measurements of O3 and PM2.5 precursors from the Reevaluating the Chemistry of Air Pollutants in California (RECAP-CA) airborne campaign and the Southwest Urban NO x and VOC Experiment (SUNVEx) ground site and mobile laboratory campaign, confirm the model's accuracy in representing NOx and many VOCs and highlight remaining biases. Although there exists an underprediction in the total VOC reactivity of observed VOC species, our model with RACM2B-VCP exhibits good agreement for VOC markers emitted from different sectors, including biogenic, fossil fuel, and VCP sources. Through sensitivity analyses, we probe the contributions of VCP and fossil fuel emissions to total VOC reactivity and O3. Our results reveal that 52% of the VOC reactivity and 35% of the local enhancement of MDA8 O3 arise from anthropogenic VOC emissions in Los Angeles. Significantly, over 50% of this anthropogenic fraction of either VOC reactivity or O3 is attributed to VCP emissions. The RACM2B-VCP mechanism created, described, and evaluated in this work is ideally suited for accurately representing ozone for the right reasons in the present urban environment where mobile, biogenic, and VCP VOCs are all important contributors to ozone formation.

Volatile chemical products (VCPs), including organic species emitted from pesticides, coatings, cleaning products, and personal care products, account for more than half of the urban VOC emissions in major North American and European cities. However, VCP emissions, spatial and temporal distributions, and impacts vary widely. Despite being the fourth largest U.S. city, Houston, Texas, lacks measured VCP concentration and emission data. This study presents the first spatial and temporal measurements of selected VCP tracers in Houston, Texas, using a Vocus 2R Chemical Ionization Mass Spectrometer on a mobile platform. Ambient measurements of five major VCP tracers, including D5-siloxane, monoterpenes, para-dichlorobenzene, para-chlorobenzotrifluoride (PCBTF), and 2,2,4-trimethyl-1,3-pentanediol isobutyrate (Texanol), were collected in winter and summer 2023. Several compounds exhibited significantly higher averaged concentrations, with pronounced spatial and seasonal variability, distinguishing Houston from urban areas in the temperate and cooler climate zone. A customized box model was employed to estimate seasonal emissions for the Greater Houston Area, showing that emissions of most VCPs were significantly higher during the summer. This study provides critical insights into the distribution and emission of VCPs in a subtropical metropolitan area, advancing methods for assessing VCP emissions and concentrations across cities and improving understandings of their impacts on air quality, climate, and public health.

Emmision of Volatile chemical products (VCPs) China: An Updated High‐Resolution Mass Balance‐Based Invenotry have emerged as a significant source of organic compound emissions in China, contributing to ozone and secondary organic aerosol (SOA) formation. Previous work established the VCP emission inventory by the mass balance (MB) method in China from 2000 to 2017, but localized component emissions and spatial variations have not been systematically investigated. This study presents a high‐resolution VCP‐gridded emission inventory in China, incorporating an updated method for emission estimation, localized source profiles, and spatial allocation. Results reveal that VCP emissions amounted to 13.88 Tg in 2022, dominated by coatings and adhesives. Industrial and domestic VCPs contribute two‐thirds and one‐third of total VCP emissions, respectively. Oxygenated volatile organic compounds (OVOCs) and aromatics constitute over 70% of total emissions and ozone formation potential (OFP), with aromatics (3.86 Tg, primarily from coatings) contributing 17.45 Tg to OFP. The component emissions of VCPs in China exhibit distinct characteristics compared to the United States, marked by higher contributions of aromatics and N/S‐containing compounds. Spatial analysis highlights industrial VCP emissions dispersed across suburban regions, whereas domestic VCP emissions are concentrated in urban cores. Key species like m/p‐xylene and methanol align with industrial emissions, whereas ethanol and D5‐siloxane match domestic emission patterns, indicative of promising application as industrial and domestic VCP tracers, respectively. The model‐ready gridded emission inventory for VCP developed in this study can be used by a chemical transport model to evaluate the impacts of VCP emissions on atmospheric chemistry and secondary pollution at different times and spatial scales in China.