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.
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.
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IJS, KILJ, NUK, PNG, UL, UM
Understanding the efficiency and variability of photochemical ozone (O3) production from western wildfire plumes is important to accurately estimate their influence on North American air quality. A ...set of photochemical measurements were made from the NOAA Twin Otter research aircraft as a part of the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) experiment. We use a zero-dimensional (0-D) box model to investigate the chemistry driving O3 production in modeled plumes. Modeled afternoon plumes reached a maximum O3 mixing ratio of 140 ± 50 ppbv (average ± standard deviation) within 20 ± 10 min of emission compared to 76 ± 12 ppbv in 60 ± 30 min in evening plumes. Afternoon and evening maximum O3 isopleths indicate that plumes were near their peak in NO x efficiency. A radical budget describes the NO x volatile - organic compound (VOC) sensitivities of these plumes. Afternoon plumes displayed a rapid transition from VOC-sensitive to NO x -sensitive chemistry, driven by HO x (=OH + HO2) production from photolysis of nitrous acid (HONO) (48 ± 20% of primary HO x ) and formaldehyde (HCHO) (26 ± 9%) emitted directly from the fire. Evening plumes exhibit a slower transition from peak NO x efficiency to VOC-sensitive O3 production caused by a reduction in photolysis rates and fire emissions. HO x production in evening plumes is controlled by HONO photolysis (53 ± 7%), HCHO photolysis (18 ± 9%), and alkene ozonolysis (17 ± 9%).
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IJS, KILJ, NUK, PNG, UL, UM
Chamber oxidation experiments conducted at the Fire Sciences Laboratory in 2016 are evaluated to identify important chemical processes contributing to the hydroxy radical (OH) chemistry of biomass ...burning non-methane organic gases (NMOGs). Based on the decay of primary carbon measured by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS), it is confirmed that furans and oxygenated aromatics are among the NMOGs emitted from western United States fuel types with the highest reactivities towards OH. The oxidation processes and formation of secondary NMOG masses measured by PTR-ToF-MS and iodide-clustering time-of-flight chemical ionization mass spectrometry (I-CIMS) is interpreted using a box model employing a modified version of the Master Chemical Mechanism (v. 3.3.1) that includes the OH oxidation of furan, 2-methylfuran, 2,5-dimethylfuran, furfural, 5-methylfurfural, and guaiacol. The model supports the assignment of major PTR-ToF-MS and I-CIMS signals to a series of anhydrides and hydroxy furanones formed primarily through furan chemistry. This mechanism is applied to a Lagrangian box model used previously to model a real biomass burning plume. The customized mechanism reproduces the decay of furans and oxygenated aromatics and the formation of secondary NMOGs, such as maleic anhydride. Based on model simulations conducted with and without furans, it is estimated that furans contributed up to 10 % of ozone and over 90 % of maleic anhydride formed within the first 4 h of oxidation. It is shown that maleic anhydride is present in a biomass burning plume transported over several days, which demonstrates the utility of anhydrides as markers for aged biomass burning plumes.
This work examines organic acid and metal concentrations in northeastern Pacific Ocean stratocumulus cloudwater samples collected by the CIRPAS Twin Otter between July and August 2011. Correlations ...between a suite of various monocarboxylic and dicarboxylic acid concentrations are consistent with documented aqueous-phase mechanistic relationships leading up to oxalate production. Monocarboxylic and dicarboxylic acids exhibited contrasting spatial profiles reflecting their different sources; the former were higher in concentration near the continent due to fresh organic emissions. Concentrations of sea salt crustal tracer species, oxalate, and malonate were positively correlated with low-level wind speed suggesting that an important route for oxalate and malonate entry in cloudwater is via some combination of association with coarse particles and gaseous precursors emitted from the ocean surface. Three case flights show that oxalate (and no other organic acid) concentrations drop by nearly an order of magnitude relative to samples in the same vicinity. A consistent feature in these cases was an inverse relationship between oxalate and several metals (Fe, Mn, K, Na, Mg, Ca), especially Fe. By means of box model studies we show that the loss of oxalate due to the photolysis of iron oxalato complexes is likely a significant oxalate sink in the study region due to the ubiquity of oxalate precursors, clouds, and metal emissions from ships, the ocean, and continental sources.
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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
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We report the emissions of glyoxal and methylglyoxal from the open burning of
biomass during the NOAA-led 2016 FIREX intensive at the Fire Sciences
Laboratory in Missoula, MT. Both compounds were ...measured using cavity-enhanced spectroscopy, which is both more sensitive and more selective than
methods previously used to determine emissions of these two compounds. A
total of 75 burns were conducted, using 33 different fuels in 8 different
categories, providing a far more comprehensive dataset for emissions than was
previously available. Measurements of methylglyoxal using our instrument
suffer from spectral interferences from several other species, and the values
reported here are likely underestimates, possibly by as much as 70 %.
Methylglyoxal emissions were 2–3 times higher than glyoxal emissions on a
molar basis, in contrast to previous studies that report methylglyoxal
emissions lower than glyoxal emissions. Methylglyoxal emission ratios for all
fuels averaged 3.6±2.4 ppbv methylglyoxal (ppmv CO)−1, while emission
factors averaged 0.66±0.50 g methylglyoxal (kg fuel burned)−1. Primary
emissions of glyoxal from biomass burning were much lower than previous
laboratory measurements but consistent with recent measurements from
aircraft. Glyoxal emission ratios for all fuels averaged 1.4±0.7 ppbv glyoxal (ppmv CO)−1, while
emission factors averaged 0.20±0.12 g glyoxal (kg fuel burned)−1, values that are at least a factor of 4 lower than
assumed in previous estimates of the global glyoxal budget. While there was
significant variability in the glyoxal emission ratios and factors between
the different fuel groups, glyoxal and formaldehyde were highly correlated
during the course of any given fire, and the ratio of glyoxal to
formaldehyde, RGF, was consistent across many different fuel
types, with an average value of 0.068±0.018. While RGF values
for fresh emissions were consistent across many fuel types, further work is
required to determine how this value changes as the emissions age.
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.
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IJS, KILJ, NUK, PNG, UL, UM
Mobile sampling studies have revealed enhanced levels of secondary organic aerosol (SOA) in source-rich urban environments. While these enhancements can be from rapidly reacting vehicular emissions, ...it was recently hypothesized that nontraditional emissions (volatile chemical products and upstream emissions) are emerging as important sources of urban SOA. We tested this hypothesis by using gas and aerosol mass spectrometry coupled with an oxidation flow reactor (OFR) to characterize pollution levels and SOA potentials in environments influenced by traditional emissions (vehicular, biogenic), and nontraditional emissions (e.g., paint fumes). We used two SOA models to assess contributions of vehicular and biogenic emissions to our observed SOA. The largest gap between observed and modeled SOA potential occurs in the morning-time urban street canyon environment, for which our model can only explain half of our observation. Contributions from VCP emissions (e.g., personal care products) are highest in this environment, suggesting that VCPs are an important missing source of precursors that would close the gap between modeled and observed SOA potential. Targeted OFR oxidation of nontraditional emissions shows that these emissions have SOA potentials that are similar, if not larger, compared to vehicular emissions. Laboratory experiments reveal large differences in SOA potentials of VCPs, implying the need for further characterization of these nontraditional emissions.
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IJS, KILJ, NUK, PNG, UL, UM
Chemical mechanisms describe the atmospheric
transformations of organic and inorganic species and connect air emissions
to secondary species such as ozone, fine particles, and hazardous air
...pollutants (HAPs) like formaldehyde. Recent advances in our understanding of
several chemical systems and shifts in the drivers of atmospheric chemistry
warrant updates to mechanisms used in chemical transport models such as the
Community Multiscale Air Quality (CMAQ) modeling system. This work builds on
the Regional Atmospheric Chemistry Mechanism version 2 (RACM2) and develops
the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM)
version 1.0, which demonstrates a fully coupled representation of chemistry
leading to ozone and secondary organic aerosol (SOA) with consideration of
HAPs. CRACMMv1.0 includes 178 gas-phase species, 51 particulate species,
and 508 reactions spanning gas-phase and heterogeneous pathways. To support
estimation of health risks associated with HAPs, nine species in CRACMM
cover 50 % of the total cancer and 60 % of the total non-cancer
emission-weighted toxicity estimated for primary HAPs from anthropogenic and
biomass burning sources in the US, with the coverage of toxicity higher
(> 80 %) when secondary formaldehyde and acrolein are
considered. In addition, new mechanism species were added based on the
importance of their emissions for the ozone, organic aerosol, or atmospheric
burden of total reactive organic carbon (ROC): sesquiterpenes, furans,
propylene glycol, alkane-like low- to intermediate-volatility organic
compounds (9 species), low- to intermediate-volatility oxygenated species (16 species), intermediate-volatility aromatic hydrocarbons (2 species), and
slowly reacting organic carbon. Intermediate- and lower-volatility organic
compounds were estimated to increase the coverage of anthropogenic and
biomass burning ROC emissions by 40 % compared to current operational
mechanisms. Autoxidation, a gas-phase reaction particularly effective in
producing SOA, was added for C10 and larger alkanes, aromatic
hydrocarbons, sesquiterpenes, and monoterpene systems including second-generation aldehydes. Integrating the radical and SOA chemistry put
additional constraints on both systems and enabled the implementation of
previously unconsidered SOA pathways from phenolic and furanone compounds,
which were predicted to account for ∼ 30 % of total aromatic
hydrocarbon SOA under typical atmospheric conditions. CRACMM organic aerosol
species were found to span the atmospherically relevant range of species carbon
number, number of oxygens per carbon, and oxidation state with a slight high
bias in the number of hydrogens per carbon. In total, 11 new emitted species
were implemented as precursors to SOA compared to current CMAQv5.3.3
representations, resulting in a bottom-up prediction of SOA, which is
required for accurate source attribution and the design of control strategies.
CRACMMv1.0 is available in CMAQv5.4.
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