Decamethylcyclopentasiloxane (D
) is a cyclic volatile methyl siloxane (cVMS) that is widely used in consumer products and commonly observed in urban air. This study quantifies the ambient mixing ...ratios of D
from ground sites in two North American cities (Boulder, CO, USA, and Toronto, ON, CA). From these data, we estimate the diurnal emission profile of D
in Boulder, CO. Ambient mixing ratios were consistent with those measured at other urban locations; however, the diurnal pattern exhibited similarities with those of traffic-related compounds such as benzene. Mobile measurements and vehicle experiments demonstrate that emissions of D
from personal care products are coincident in time and place with emissions of benzene from motor vehicles. During peak commuter times, the D
/benzene ratio (w/w) is in excess of 0.3, suggesting that the mass emission rate of D
from personal care product usage is comparable to that of benzene due to traffic. The diurnal emission pattern of D
is estimated using the measured D
/benzene ratio and inventory estimates of benzene emission rates in Boulder. The hourly D
emission rate is observed to peak between 6:00 and 7:00 AM and subsequently follow an exponential decay with a time constant of 9.2 h. This profile could be used by models to constrain temporal emission patterns of personal care products.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
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 (
∼ 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,
-dichlorobenzene for insecticides, D4-siloxane for adhesives,
-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.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Concentrated animal feeding operations (CAFOs) emit a large number of volatile organic compounds (VOCs) to the atmosphere. In this study, we conducted mobile laboratory measurements of VOCs, methane ...(CH4) and ammonia (NH3) downwind of dairy cattle, beef cattle, sheep and chicken CAFO facilities in northeastern Colorado using a hydronium ion time-of-flight chemical-ionization mass spectrometer (H3O+ ToF-CIMS), which can detect numerous VOCs. Regional measurements of CAFO emissions in northeastern Colorado were also performed using the NOAA WP-3D aircraft during the Shale Oil and Natural Gas Nexus (SONGNEX) campaign. Alcohols and carboxylic acids dominate VOC concentrations and the reactivity of the VOCs with hydroxyl (OH) radicals. Sulfur-containing and phenolic species provide the largest contributions to the odor activity values and the nitrate radical (NO3) reactivity of VOC emissions, respectively. VOC compositions determined from mobile laboratory and aircraft measurements generally agree well with each other. The high time-resolution mobile measurements allow for the separation of the sources of VOCs from different parts of the operations occurring within the facilities. We show that the emissions of ethanol are primarily associated with feed storage and handling. Based on mobile laboratory measurements, we apply a multivariate regression analysis using NH3 and ethanol as tracers to determine the relative importance of animal-related emissions (animal exhalation and waste) and feed-related emissions (feed storage and handling) for different VOC species. Feed storage and handling contribute significantly to emissions of alcohols, carbonyls, carboxylic acids and sulfur-containing species. Emissions of phenolic species and nitrogen-containing species are predominantly associated with animals and their waste.
Ozone is a key constituent of the troposphere, where it drives photochemical processes, impacts air quality, and acts as a climate forcer. Large-scale in situ observations of ozone commensurate with ...the grid resolution of current Earth system models are necessary to validate model outputs and satellite retrievals. In this paper, we examine measurements from the Atmospheric Tomography (ATom; four deployments in 2016–2018) and the HIAPER Pole-to-Pole Observations (HIPPO; five deployments in 2009–2011) experiments, two global-scale airborne campaigns covering the Pacific and Atlantic basins.
ATom and HIPPO represent the first global-scale, vertically resolved measurements of O3 distributions throughout the troposphere, with HIPPO sampling the atmosphere over the Pacific and ATom sampling both the Pacific and Atlantic. Given the relatively limited temporal resolution of these two campaigns, we first compare ATom and HIPPO ozone data to longer-term observational records to establish the representativeness of our dataset. We show that these two airborne campaigns captured on average 53 %, 54 %, and 38 % of the ozone variability in the marine boundary layer, free troposphere, and upper troposphere–lower stratosphere (UTLS), respectively, at nine well-established ozonesonde sites. Additionally, ATom captured the most frequent ozone concentrations measured by regular commercial aircraft flights in the northern Atlantic UTLS. We then use the repeated vertical profiles from these two campaigns to confirm and extend the existing knowledge of tropospheric ozone spatial and vertical distributions throughout the remote troposphere. We highlight a clear hemispheric gradient, with greater ozone in the Northern Hemisphere, consistent with greater precursor emissions and consistent with previous modeling and satellite studies. We also show that the ozone distribution below 8 km was similar in the extra-tropics of the Atlantic and Pacific basins, likely due to zonal circulation patterns. However, twice as much ozone was found in the tropical Atlantic as in the tropical Pacific, due to well-documented dynamical patterns transporting continental air masses over the Atlantic. Finally, we show that the seasonal variability of tropospheric ozone over the Pacific and the Atlantic basins is driven year-round by transported continental plumes and photochemistry, and the vertical distribution is driven by photochemistry and mixing with stratospheric air. This new dataset provides additional constraints for global climate and chemistry models to improve our understanding of both ozone production and loss processes in remote regions, as well as the influence of anthropogenic emissions on baseline ozone.
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.
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.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Volatile organic compounds (VOCs) emitted from residential wood and crop residue burning were measured in Colorado, U.S. When compared to the emissions from crop burning, residential wood burning ...exhibited markedly lower concentrations of acetonitrile, a commonly used biomass burning tracer. For both herbaceous and arboraceous fuels, the emissions of nitrogen‐containing VOCs (NVOCs) strongly depend on the fuel nitrogen content; therefore, low NVOC emissions from residential wood burning result from the combustion of low‐nitrogen fuel. Consequently, the emissions of compounds hazardous to human health, such as HNCO and HCN, and the formation of secondary pollutants, such as ozone generated by NOx, are likely to depend on fuel nitrogen. These results also demonstrate that acetonitrile may not be a suitable tracer for domestic burning in urban areas. Wood burning emissions may be best identified through analysis of the emissions profile rather than reliance on a single tracer species.
Key Points
The emissions of nitrogen‐containing VOCs from biomass burning smoke is strongly dependent on fuel composition
Common biomass burning markers, such as acetonitrile, are weakly associated with emissions from residential wood burning
The emissions of hazardous nitrogen‐containing compounds, such as HNCO and HCN, will depend on fuel nitrogen content
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Atmospheric emissions from animal husbandry are important to both air quality and climate, but are hard to characterize and quantify as they differ significantly due to management practices and ...livestock type, and they can vary substantially throughout diurnal and seasonal cycles. Using a new mobile laboratory, ammonia (NH3), methane (CH4), nitrous oxide (N2O), and other trace gas emissions were measured from four concentrated animal feeding operations (CAFOs) in northeastern Colorado. Two dairies, a beef cattle feedlot, and a sheep feedlot were chosen for repeated diurnal and seasonal measurements. A consistent diurnal pattern in the NH3 to CH4 enhancement ratio is clearly observed, with midday enhancement ratios approximately four times greater than nighttime values. This diurnal pattern is similar, with slight variations in magnitude, at the four CAFOs and across seasons. The average NH3 to CH4 enhancement ratio from all seasons and CAFOs studied is 0.17 (+0.13/–0.08) mol/mol, in agreement with statewide inventory averages and previous literature. Enhancement ratios for NH3 to N2O and N2O to CH4 are also reported. The enhancement ratios can be used as a source signature to distinguish feedlot emissions from other NH3 and CH4 sources, such as fertilizer application and fossil fuel development, and the large diurnal variability is important for refining inventories, models, and emission estimates.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
Ozone is the third most important anthropogenic greenhouse gas after carbon dioxide and methane but has a larger uncertainty in its radiative forcing, in part because of uncertainty in the source ...characteristics of ozone precursors, nitrogen oxides, and volatile organic carbon that directly affect ozone formation chemistry. Tropospheric ozone also negatively affects human and ecosystem health. Biomass burning (BB) and urban emissions are significant but uncertain sources of ozone precursors. Here, we report global-scale, in situ airborne measurements of ozone and precursor source tracers from the NASA Atmospheric Tomography mission. Measurements from the remote troposphere showed that tropospheric ozone is regularly enhanced above background in polluted air masses in all regions of the globe. Ozone enhancements in air with high BB and urban emission tracers (2.1 to 23.8 ppbv parts per billion by volume) were generally similar to those in BB-influenced air (2.2 to 21.0 ppbv) but larger than those in urban-influenced air (-7.7 to 6.9 ppbv). Ozone attributed to BB was 2 to 10 times higher than that from urban sources in the Southern Hemisphere and the tropical Atlantic and roughly equal to that from urban sources in the Northern Hemisphere and the tropical Pacific. Three independent global chemical transport models systematically underpredict the observed influence of BB on tropospheric ozone. Potential reasons include uncertainties in modeled BB injection heights and emission inventories, export efficiency of BB emissions to the free troposphere, and chemical mechanisms of ozone production in smoke. Accurately accounting for intermittent but large and widespread BB emissions is required to understand the global tropospheric ozone burden.
Nitrogen oxides (NOx = NO + NO2) emitted by on-road combustion engines are important contributors to tropospheric ozone production. The NOx fraction emitted as nitrogen dioxide (NO2) is usually ...presumed to be small but can affect ozone production and distribution, and this fraction is generally not reported in emissions inventories. We have developed an accurate method for determination of this primary NO2 emission and demonstrated it during measurement of on-road vehicle emission plumes from a mobile laboratory during July and August 2014 in the region between Denver and Greeley in Colorado. During a total of approximately 90 h of sampling from an instrumented mobile laboratory, we identified 1867 vehicle emission plumes, which were extracted using an algorithm that looks for rapid and large increases in measured NOx. We find a distribution of NO2/NOx emissions similar to a log-normal profile, with an average emission ratio of 0.053 ± 0.002 per sampled NOx plume. The average is not weighted by the total NOx emissions from sampled vehicles, which is not measured here, and so may not represent the NO2/NOx ratio of the total NOx emission if this ratio is a function of NOx itself. Although our current data set does not distinguish between different engine types (e.g., gasoline, light duty diesel and heavy duty diesel), the ratio is on the low end of recent reports of vehicle fleet NO2 to NOx emission ratios in Europe.
•A new method for measurement of vehicle NO2/NOx using fast response Ox/NOx in plumes.•Statistics from a sample of >1800 exhaust plumes measured on-road near Denver, CO.•Plume average NO2/NOx is 5.3%, not weighted for NOx mass emissions.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
PDF
