Biomass burning is the largest combustion-related source of volatile organic compounds (VOCs) to the atmosphere. We describe the development of a state-of-the-science model to simulate the ...photochemical formation of secondary organic aerosol (SOA) from biomass-burning emissions observed in dry (RH <20%) environmental chamber experiments. The modeling is supported by (i) new oxidation chamber measurements, (ii) detailed concurrent measurements of SOA precursors in biomass-burning emissions, and (iii) development of SOA parameters for heterocyclic and oxygenated aromatic compounds based on historical chamber experiments. We find that oxygenated aromatic compounds, including phenols and methoxyphenols, account for slightly less than 60% of the SOA formed and help our model explain the variability in the organic aerosol mass (R 2 = 0.68) and O/C (R 2 = 0.69) enhancement ratios observed across 11 chamber experiments. Despite abundant emissions, heterocyclic compounds that included furans contribute to ∼20% of the total SOA. The use of pyrolysis-temperature-based or averaged emission profiles to represent SOA precursors, rather than those specific to each fire, provide similar results to within 20%. Our findings demonstrate the necessity of accounting for oxygenated aromatics from biomass-burning emissions and their SOA formation in chemical mechanisms.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
Volatile terpenes serve multiple biological roles including tree resistance against herbivores. The increased frequency and severity of drought stress observed in forests across the globe ...may hinder trees from producing defense-related volatiles in response to biotic stress. To assess how drought-induced physiological stress alters volatile emissions alone and in combination with a biotic challenge, we monitored pre-dawn water potential, gas-exchange, needle terpene concentrations and terpene volatile emissions of ponderosa pine (Pinus ponderosa) saplings during three periods of drought and in response to simulated herbivory via methyl jasmonate application. Although 3-, 6- and 7-week drought treatments reduced net photosynthetic rates by 20, 89 and 105%, respectively, the magnitude of volatile fluxes remained generally resistant to drought. Herbivore-induced emissions, however, exhibited threshold-like behavior; saplings were unable to induce emissions above constitutive levels when pre-dawn water potentials were below the approximate zero-assimilation point. By comparing compositional shifts in emissions to needle terpene concentrations, we found evidence that drought effects on constitutive and herbivore-induced volatile flux and composition are primarily via constraints on the de novo fraction, suggesting that reduced photosynthesis during drought limits the carbon substrate available for de novo volatile synthesis. However, results from a subsequent 13CO2 pulse-chase labeling experiment then confirmed that both constitutive (<3% labeled) and herbivore-induced (<8% labeled) de novo emissions from ponderosa pine are synthesized predominantly from older carbon sources with little contribution from new photosynthates. Taken together, we provide evidence that in ponderosa pine, drought does not constrain herbivore-induced de novo emissions through substrate limitation via reduced photosynthesis, but rather through more sophisticated molecular and/or biophysical mechanisms that manifest as saplings reach the zero-assimilation point. These results highlight the importance of considering drought severity when assessing impacts on the herbivore-induced response and suggest that drought-altered volatile metabolism constrains induced emissions once a physiological threshold is surpassed.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Observations of total peroxy radical concentrations
(XO2 ≡ RO2 + HO2) made
by the Ethane CHemical AMPlifier (ECHAMP) and concomitant observations of
additional trace gases made on board the Aerodyne ...Mobile Laboratory (AML)
during May 2017 were used to characterize ozone production at three sites in
the San Antonio, Texas, region. Median daytime O3 was 48 ppbv at
the site downwind of central San Antonio. Higher concentrations of NO and
XO2 at the downwind site also led to median daytime ozone
production rates (P(O3)) of 4.2 ppbv h−1, a factor
of 2 higher than at the two upwind sites. The 95th percentile of
P(O3) at the upwind site was 15.1 ppbv h−1,
significantly lower than values observed in Houston. In situ observations,
as well as satellite retrievals of HCHO and NO2, suggest that the
region was predominantly NOx-limited. Only approximately
20 % of observations were in the VOC-limited regime, predominantly before
11:00 EST, when ozone production was low. Biogenic volatile organic
compounds (VOCs) comprised 55 % of total OH reactivity at the downwind
site, with alkanes and non-biogenic alkenes responsible for less than
10 % of total OH reactivity in the afternoon, when ozone production was
highest. To control ozone formation rates at the three study sites
effectively, policy efforts should be directed at reducing
NOx emissions. Observations in the urban center of San
Antonio are needed to determine whether this policy is true for the entire
region.
Diesel-powered vehicles are intensively used in urban areas for transporting goods and people but can substantially contribute to high emissions of black carbon (BC), organic carbon (OC), and other ...gaseous pollutants. Strategies aimed at controlling mobile emissions sources thus have the potential to improve air quality and help mitigate the impacts of air pollutants on climate, ecosystems, and human health. However, in developing countries there are limited data on the BC and OC emission characteristics of diesel-powered vehicles, and thus there are large uncertainties in the estimation of the emission contributions from these sources. We measured BC, OC, and other inorganic components of fine particulate matter (PM), as well as carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), ethane, acetylene, benzene, toluene, and C2-benzenes under real-world driving conditions for 20 diesel-powered vehicles encompassing multiple emission level technologies in Mexico City with the chasing technique using the Aerodyne mobile laboratory. Average BC emission factors ranged from 0.41–2.48 g kg−1 of fuel depending on vehicle type. The vehicles were also simultaneously measured using the cross-road remote sensing technique to obtain the emission factors of nitrogen oxide (NO), CO, total hydrocarbons, and fine PM, thus allowing for the intercomparison of the results from the two techniques. There is overall good agreement between the two techniques and both can identify high and low emitters, but substantial differences were found in some of the vehicles, probably due to the ability of the chasing technique to capture a larger diversity of driving conditions in comparison to the remote sensing technique. A comparison of the results with the US EPA MOVES2014b model showed that the model underestimates CO, OC, and selected VOC species, whereas there is better agreement for NOx and BC. Larger OC / BC ratios were found in comparison to ratios measured in California using the same technique, further demonstrating the need for using locally obtained diesel-powered vehicle emission factor database in developing countries in order to reduce the uncertainty in the emissions estimates and to improve the evaluation of the effectiveness of emissions reduction measures.
Ozone (O3), a potent greenhouse gas that is detrimental to human health, is typically found in elevated concentrations within biomass burning (BB) smoke plumes. The radical species OH, HO2, and RO2 ...(known collectively as ROx) have central roles in the formation of secondary pollutants including O3 but are poorly characterized for BB plumes. We present measurements of total peroxy radical concentrations (XO2 ≡ HO2 + RO2) and additional trace-gas and particulate matter measurements from McCall, Idaho, during August 2018. There were five distinct periods in which BB smoke impacted this site. During BB events, O3 concentrations were enhanced, evident by ozone enhancement ratios (ΔO3/ΔCO) that ranged up to 0.06 ppbv ppbv-1. XO2 was similarly elevated during some BB events. Overall, instantaneous ozone production rates (P(O3)) were minimally impacted by the presence of smoke as NOx enhancements were minimal. Measured XO2 concentrations were compared to zero-dimensional box modeling results to evaluate the Master Chemical Mechanism (MCM) and GEOS-Chem mechanisms overall and during periods of BB influence. The models consistently overestimated XO2 with the base MCM and GEOS-Chem XO2 predictions high by an average of 28 % and 20 %, respectively. One period of BB influence had distinct measured enhancements of 15 pptv XO2 that were not reflected in the model output, likely due to the presence of unmeasured HOx sources. To the best of our knowledge, this is the first BB study featuring peroxy radical measurements.
In many parts of the developing world and economies in transition, small-scale traditional brick kilns are a notorious source of urban air pollution. Many are both energy inefficient and burn highly ...polluting fuels that emit significant levels of black carbon (BC), organic carbon (OC) and other atmospheric pollutants into local communities, resulting in severe health and environmental impacts. However, only a very limited number of studies are available on the emission characteristics of brick kilns; thus, there is a need to characterize their gaseous and particulate matter (PM) emission factors to better assess their overall contribution to emissions inventories and to quantify their ecological, human health, and climate impacts. In this study, the fuel-, energy-, and brick-based emissions factors and time-based emission ratios of BC, OC, inorganic PM components, CO, SO2, CH4, NOx, and selected volatile organic compounds (VOCs) from three artisanal brick kilns with different designs in Mexico were quantified using the tracer ratio sampling technique. Simultaneous measurements of PM components, CO, and CO2 were also obtained using a sampling probe technique. Additional measurements included the internal temperature of the brick kilns, mechanical resistance of bricks produced, and characteristics of fuels employed. Average fuel-based BC emission factors ranged from 0.15 to 0.58 g (kg fuel)−1, whereas BC∕OC mass ratios ranged from 0.9 to 5.2, depending on the kiln type. The results show that both techniques capture similar temporal profiles of the brick kiln emissions and produce comparable emission factors. A more integrated inter-comparison of the brick kilns' performances was obtained by simultaneously assessing emissions factors, energy efficiency, fuel consumption, and the quality of the bricks produced.
An Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed during the Carbonaceous Aerosols and Radiative Effects Study (CARES) that took place in northern ...California in June 2010. We present results obtained at Cool (denoted as the T1 site of the project) in the foothills of the Sierra Nevada Mountains, where intense biogenic emissions are periodically mixed with urban outflow transported by daytime southwesterly winds from the Sacramento metropolitan area. During this study, the average mass loading of submicrometer particles (PM1) was 3.0 μg m−3, dominated by organics (80%) and sulfate (9.9%). The organic aerosol (OA) had a nominal formula of C1H1.38N0.004OM0.44, thus an average organic mass-to-carbon (OM/OC) ratio of 1.70. Two distinct oxygenated OA factors were identified via Positive matrix factorization (PMF) of the high-resolution mass spectra of organics. The more oxidized MO-OOA (O/C = 0.54) was interpreted as a surrogate for secondary OA (SOA) influenced by biogenic emissions whereas the less oxidized LO-OOA (O/C = 0.42) was found to represent SOA formed in photochemically processed urban emissions. LO-OOA correlated strongly with ozone and MO-OOA correlated well with two 1st generation isoprene oxidation products (methacrolein and methyl vinyl ketone), indicating that both SOAs were relatively fresh. A hydrocarbon like OA (HOA) factor was also identified, representing primary emissions mainly due to local traffic. On average, SOA (= MO-OOA + LO-OOA) accounted for 91% of the total OA mass and 72% of the PM1 mass observed at Cool. Twenty three periods of urban plumes from T0 (Sacramento) to T1 (Cool) were identified using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). The average PM1 mass loading was considerably higher in urban plumes than in air masses dominated by biogenic SOA. The change in OA mass relative to CO (ΔOA/ΔCO) varied in the range of 5-196 μg m−3 ppm−1, reflecting large variability in SOA production. The highest ΔOA/ΔCO was reached when air masses were dominated by anthropogenic emissions in the presence of a high concentration of biogenic volatile organic compounds (BVOCs). This ratio, which was 97 μg m−3 ppm−1 on average, was much higher than when urban plumes arrived in a low BVOC environment (~36 μg m−3 ppm−1) or during other periods dominated by biogenic SOA (35 μg m−3 ppm−1). These results demonstrate that SOA formation is enhanced when anthropogenic emissions interact with biogenic precursors.
A wide array of volatile organic compound (VOC) measurements was conducted in the Valley of Mexico during the MCMA-2002 and 2003 field campaigns. Study sites included locations in the urban core, in ...a heavily industrial area and at boundary sites in rural landscapes. In addition, a novel mobile-laboratory-based conditional sampling method was used to collect samples dominated by fresh on-road vehicle exhaust to identify those VOCs whose ambient concentrations were primarily due to vehicle emissions. Four distinct analytical techniques were used: whole air canister samples with Gas Chromatography/Flame Ionization Detection (GC-FID), on-line chemical ionization using a Proton Transfer Reaction Mass Spectrometer (PTR-MS), continuous real-time detection of olefins using a Fast Olefin Sensor (FOS), and long path measurements using UV Differential Optical Absorption Spectrometers (DOAS). The simultaneous use of these techniques provided a wide range of individual VOC measurements with different spatial and temporal scales. The VOC data were analyzed to understand concentration and spatial distributions, diurnal patterns, origin and reactivity in the atmosphere of Mexico City. The VOC burden (in ppbC) was dominated by alkanes (60%), followed by aromatics (15%) and olefins (5%). The remaining 20% was a mix of alkynes, halogenated hydrocarbons, oxygenated species (esters, ethers, etc.) and other unidentified VOCs. However, in terms of ozone production, olefins were the most relevant hydrocarbons. Elevated levels of toxic hydrocarbons, such as 1,3-butadiene, benzene, toluene and xylenes, were also observed. Results from these various analytical techniques showed that vehicle exhaust is the main source of VOCs in Mexico City and that diurnal patterns depend on vehicular traffic in addition to meteorological processes. Finally, examination of the VOC data in terms of lumped modeling VOC classes and its comparison to the VOC lumped emissions reported in other photochemical air quality modeling studies suggests that some alkanes are underestimated in the emissions inventory, while some olefins and aromatics are overestimated.
Ozone (O.sub.3 ), a potent greenhouse gas that is detrimental to human health, is typically found in elevated concentrations within biomass burning (BB) smoke plumes. The radical species OH, ...HO.sub.2, and RO.sub.2 (known collectively as RO.sub.x) have central roles in the formation of secondary pollutants including O.sub.3 but are poorly characterized for BB plumes. We present measurements of total peroxy radical concentrations (XO.sub.2 â¡ HO.sub.2 + RO.sub.2 ) and additional trace-gas and particulate matter measurements from McCall, Idaho, during August 2018. There were five distinct periods in which BB smoke impacted this site. During BB events, O.sub.3 concentrations were enhanced, evident by ozone enhancement ratios (ÎO3/ÎCO) that ranged up to 0.06 ppbv ppbv.sup.-1 . XO.sub.2 was similarly elevated during some BB events. Overall, instantaneous ozone production rates (P(O.sub.3 )) were minimally impacted by the presence of smoke as NO.sub.x enhancements were minimal. Measured XO.sub.2 concentrations were compared to zero-dimensional box modeling results to evaluate the Master Chemical Mechanism (MCM) and GEOS-Chem mechanisms overall and during periods of BB influence. The models consistently overestimated XO.sub.2 with the base MCM and GEOS-Chem XO.sub.2 predictions high by an average of 28 % and 20 %, respectively. One period of BB influence had distinct measured enhancements of 15 pptv XO.sub.2 that were not reflected in the model output, likely due to the presence of unmeasured HO.sub.x sources. To the best of our knowledge, this is the first BB study featuring peroxy radical measurements.
Ozone (O3), a potent greenhouse gas that is detrimental to
human health, is typically found in elevated concentrations within biomass
burning (BB) smoke plumes. The radical species OH, HO2, and RO2
...(known collectively as ROx) have central roles in the formation of secondary
pollutants including O3 but are poorly characterized for BB plumes. We
present measurements of total peroxy radical concentrations (XO2 ≡ HO2 + RO2) and additional trace-gas and
particulate matter measurements from McCall, Idaho, during August 2018. There
were five distinct periods in which BB smoke impacted this site. During BB
events, O3 concentrations were enhanced, evident by ozone
enhancement ratios (ΔO3/ΔCO) that ranged up to 0.06 ppbv ppbv−1. XO2 was similarly elevated during some BB events.
Overall, instantaneous ozone production rates (P(O3)) were
minimally impacted by the presence of smoke as NOx enhancements were minimal. Measured XO2 concentrations were compared to zero-dimensional
box modeling results to evaluate the Master Chemical
Mechanism (MCM) and GEOS-Chem mechanisms overall and during periods of BB
influence. The models consistently overestimated XO2 with the base MCM
and GEOS-Chem XO2 predictions high by an average of 28 % and 20 %,
respectively. One period of BB influence had distinct measured enhancements
of 15 pptv XO2 that were not reflected in the model output, likely due
to the presence of unmeasured HOx sources. To the best of our knowledge, this is the
first BB study featuring peroxy radical measurements.
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