Top PDF Investigation of Fundamental Processes Governing Secondary Organic Aerosol Formation in Laboratory Chambers

Investigation of Fundamental Processes Governing Secondary Organic Aerosol Formation in Laboratory Chambers

Investigation of Fundamental Processes Governing Secondary Organic Aerosol Formation in Laboratory Chambers

Figure 11 (A) shows the simulated SOA growth (SIM.1) using the initial conditions in Exp. #2, together with the observed total organic aerosol mass as a function of reaction time and OH exposure. The model reproduces the chamber measured SOA yield at 3% RH when the conversion rate of 3 × 10 -3 s -1 is employed to represent the heterogeneous conversion of δ-hydroxycarbonyl to dihydrofuran. A second simulation (SIM.2) was run with the complete dihydrofuran chemistry removed while other parameters were held constant. The total organic mass is ~ 42% higher as a result after 18 h photooxidation. The formation of alkyl-substituted dihydrofuran from δ-hydroxycarbonyl is accompanied by an increase of vapor pressure from 5.36 × 10 -7 to 1.08 × 10 -4 atm at 300 K, as predicted by SIMPOL.1, and the total organic mass formed decreases. Although the addition of OH to the C=C double bond in the substituted dihydrofuran introduces an extra OH group, the decrease of vapor pressure owing to the addition of one OH group does not compensate for the heterogeneous conversion of both –C=O and –OH groups in δ -hydroxycarbonyl to an –O– group in a non-aromatic ring in dihydrofuran. The predicted the average carbon oxidation state is ~ 7 – 15% higher than observations. The overprediction is within the uncertainties in the O:C (31%) and H:C (10%) measurement by AMS (Aiken et al., 2008). Incorporation of the substituted dihydrofuran formation and removal pathways in the model leads to an increase in the simulated OS C . Compared with
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Modeling the Effect of Vapor Wall Deposition on the Formation of Secondary Organic Aerosol in Chamber Studies

Modeling the Effect of Vapor Wall Deposition on the Formation of Secondary Organic Aerosol in Chamber Studies

Laboratory chambers, invaluable in atmospheric chemistry and aerosol formation studies, are subject to particle and vapor wall deposition, processes that need to be accounted for in order to accurately determine secondary organic aerosol (SOA) mass yields. Although particle wall deposition is rea- sonably well understood and usually accounted for, vapor wall deposition is less so. The effects of vapor wall deposition on SOA mass yields in chamber experiments can be constrained exper- imentally by increasing the seed aerosol surface area to promote the preferential condensation of SOA-forming vapors onto seed aerosol. Here, we study the influence of seed aerosol surface area and oxidation rate on SOA formation in α-pinene ozonolysis. The observations are analyzed using a coupled vapor-particle dynamics model to interpret the roles of gas-particle partitioning (quasi- equilibrium vs. kinetically-limited SOA growth) and α-pinene oxidation rate in influencing vapor wall deposition. We find that the SOA growth rate and mass yields are independent of seed surface area within the range of seed surface area concentrations used in this study. This behavior arises when the condensation of SOA-forming vapors is dominated by quasi-equilibrium growth. Faster α-pinene oxidation rates and higher SOA mass yields are observed at increasing O 3 concentrations for the same initial α-pinene concentration. When the α-pinene oxidation rate increases relative to vapor wall deposition, rapidly produced SOA-forming oxidation products condense more readily onto seed aerosol particles, resulting in higher SOA mass yields. Our results indicate that the extent to which vapor wall deposition affects SOA mass yields depends on the particular VOC system, and can be mitigated through the use of excess oxidant concentrations.
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A new aerosol flow reactor to study secondary organic aerosol

A new aerosol flow reactor to study secondary organic aerosol

The CFR was designed to generate larger quantities of SOA mass than achieved in most studies for offline chemical com- position and single-particle analysis. Single-particle mea- surement techniques, such as an electrodynamic balance and aerosol optical tweezers, can provide information on the mor- phology, hygroscopicity and phase behaviour of SOA with unprecedented accuracy (see Krieger et al., 2012, for further information). These techniques allow the effect of environ- mental changes on the microphysical state of the SOA to be investigated in controlled laboratory conditions, allowing the fundamental processes governing gas-particle partition- ing to be better understood. These techniques, however, re- quire considerable quantities of SOA mass for ease of trans- fer to particle generators (> 20 mg of SOA per experiment). To achieve this quantity of SOA mass, high mixing ratios (i.e. parts-per-million by volume) of a VOC precursor and oxidants must be continuously introduced into a reactor over several hours of operation. The CFR is ideally suited for this application in comparison to larger and well-established at- mospheric simulation chambers, due to the ability to quickly and easily clean the reactor lines and replace the sampling bag at minimal cost (GBP ∼ 400).
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Characterization of aerosol photooxidation flow reactors: heterogeneous oxidation, secondary organic aerosol formation and cloud condensation nuclei activity measurements

Characterization of aerosol photooxidation flow reactors: heterogeneous oxidation, secondary organic aerosol formation and cloud condensation nuclei activity measurements

Flow tube reactors, with volumes typically in the range of 0.001–0.01 m 3 , provide aerosol residence times of seconds to minutes. Despite shorter residence times, much higher oxidant concentrations are attainable, which facilitate higher exposure times equivalent to 1–2 weeks of atmospheric oxi- dation. Further, experiments that may take hours in a smog chamber can be performed in minutes in a flow tube, under conditions that can be better controlled with respect to ox- idant concentration, contamination (Lonneman et al., 1981; Joshi et al., 1982) and wall interactions (McMurry and Rader, 1985; McMurry and Grosjean, 1985; Pierce et al., 2008). On the other hand, smog chambers with lower oxidant con- centrations and longer residence times may more closely simulate atmospheric oxidation. All laboratory reactors are imperfect simulations of the atmosphere because they have walls that cause particle loss and can influence the chemistry of semivolatile organics and, thus, particle growth and com- position (Matsunaga and Ziemann, 2010). Therefore, utiliz- ing flow tubes and smog chamber reactors with different de- signs can complement each other, making it possible to ex- tend studies over a range of parameters unattainable by either method individually, and ultimately lead towards a better un- derstanding of atmospheric aerosol processes. The results of laboratory aerosol experiments are used as inputs to climate models. Therefore, the evaluation of experimental uncertain- ties associated with measurements is needed for reliable ap- plication. The characterization of different reactor designs is important to establish the reliability of the experimental techniques.
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Understanding global secondary organic aerosol amount and size-resolved condensational behavior

Understanding global secondary organic aerosol amount and size-resolved condensational behavior

Regarding the uncertain amount of SOA, the global bud- get of SOA is highly unconstrained with bottom-up and top-down estimates ranging from 12 to 1820 Tg (SOA) yr −1 (Goldstein and Galbally, 2007; Hallquist et al., 2009; Kanakidou et al., 2005). This uncertainty in the amount of condensing SOA available has important implications on the growth of ultrafine particles as well. Many global models only contain biogenic sources of SOA (and small contribu- tions from anthropogenic SOA) with emissions generally be- tween 10 and 30 Tg yr −1 (Pierce et al., 2011; Spracklen et al., 2006; Wainwright et al., 2012), on the low end of the uncertainty range. However, by comparing GLOMAP global model simulations to aerosol mass spectrometer measure- ments or organic aerosol mass, Spracklen et al. (2011b) were able to significantly improve the model prediction of organic aerosol mass by adding an additional 100 Tg yr −1 of SOA spatially correlated with anthropogenic carbon monoxide (CO) emissions. That additional SOA increases the amount of condensable material in the atmosphere, which increases growth rates of ultrafine particles; however, the extra mass also increases the condensation and coagulation sinks of small particles, which will slow their growth rates and in- crease their coagulational losses. Thus, it is unclear what overall effect the extra SOA will have on CCN.
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Fluvial processes in compound straight channels: a laboratory investigation

Fluvial processes in compound straight channels: a laboratory investigation

uniform sediments is used by Knight and Brown [4], Myers et al. [8], Knight et al. [14], Atabay et al. [15], Tang and Knight [16] and Bousmar et al. [17] in their laboratory investigation. In practice, it is hardly to found a river bed with a uniform size of sediment particles. Thus, the main reason for using uniform graded sand in this study is to minimise the influence of the “sheltering” and “hiding” effects. As bed forms propagate to the downstream, sediment moves from the crest of the bed forms to the trough. In the trough, the sediment is sheltered and overlaid by the advancing grains from the upstream bed forms [18].
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primary and secondary processes, formation of H 2 S,

primary and secondary processes, formation of H 2 S,

after the incorporation of one deuterium atom in 100% of the molecules of 9; iii) the theoretical isotopic distribution of 9 obtained after the incorporation of two deuterium atoms in 1[r]

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LABORATORY INVESTIGATION OF WARM ASPHALT CHEMICAL AND ORGANIC ADDITIVES

LABORATORY INVESTIGATION OF WARM ASPHALT CHEMICAL AND ORGANIC ADDITIVES

Sasobit Additive Organic additives, that have melting points below a normal asphalt production temperature, can be added to asphalt to reduce its viscosity.. With organic additives, the [r]

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Formation of Secondary Organic Aerosols by Germicidal Ultraviolet Light

Formation of Secondary Organic Aerosols by Germicidal Ultraviolet Light

particulate matter (PM2.5) size range was measured, and significant levels of particle formation 17.. were observed for UV exposure periods of as short as 5 minutes.[r]

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Light extinction by secondary organic aerosol: an intercomparison of three broadband cavity spectrometers

Light extinction by secondary organic aerosol: an intercomparison of three broadband cavity spectrometers

Over the last decade, optical cavity methods have greatly advanced the characterization of aerosols (Pettersson et al., 2004; Moosmüller et al., 2009; Miles et al., 2011; Abo Riziq et al., 2007). The high sensitivity of these methods results from the very long effective path lengths – typically hundreds of metres to tens of kilometres – that are achieved inside high-finesse optical cavities. Sensitive and accurate aerosol extinction coefficient measurements can also be combined with a separate measurement of the scattering coefficient in the so-called extinction-minus-scattering approach to re- trieve the aerosol absorption. Cavity ring-down spectroscopy (CRDS) has been used by several groups for laboratory, field, and airborne studies of aerosol optical properties (Smith and Atkinson, 2001; Moosmüller et al., 2005; Strawa et al., 2003; Thompson et al., 2002; Ma and Thompson, 2012). Extinction coefficient detection limits of well below 1 Mm −1 (equiva- lent to 10 −8 cm −1 ) have been demonstrated with CRDS sys- tems (Moosmüller et al., 2009). A related method, cavity attenuated phase shift (CAPS) spectroscopy, has also been used for quantifying aerosol extinction over a narrow wave- length band (Kebabian et al., 2007; Massoli et al., 2010). Although Miles et al. (2010) have recently demonstrated a CRDS system for measuring aerosol extinction spectra, typ- ical CRDS and CAPS system are limited to one or two wave- lengths; moreover, care must be taken to account for gas ab- sorption when quantifying the aerosol extinction.
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Modeling regional air quality and climate: improving organic aerosol and aerosol activation processes in WRF/Chem version 3.7.1

Modeling regional air quality and climate: improving organic aerosol and aerosol activation processes in WRF/Chem version 3.7.1

Statistical measures including the mean bias (MB), corre- lation coefficient (Corr), normalized mean bias (NMB) and normalized mean error (NME) (Yu et al., 2006) are used to evaluate the simulations against observational data. Obser- vational data are available for organic carbon (OC) and to- tal carbon (TC) from the Speciated Trends Network (STN) and the Interagency Monitoring for Protected Visual Envi- ronments (IMPROVE). While both OC and TC from IM- PROVE are used for model evaluation, only TC data from STN are used, as STN uses the thermo-optical transmittance protocol for OC that is different from the one used by IM- PROVE (Zhang et al., 2012). In addition, the measurements for STN OC are not blank corrected for carbon on the back- ground filter (Wang and Zhang, 2012). The OA / OC ratios vary across locations in the continental US (CONUS) de- pending on whether the OA is dominated by secondary for- mation (Aitken et al., 2008) or it contains more aliphatic hy- drocarbons (Turpin and Lim, 2001). In this study, two ratios, 1.4 and 2.1, are used to convert simulated OA to OC based on a number of studies in the literature (Turpin and Lim, 2001; Aitken et al., 2008; Xu et al., 2015). As the simula- tions are based on CONUS with varying OA properties (less or more oxidized OA), the use of two OA / OC ratios can represent the different types of OA present for all locations in the US. Spatial plots, time series plots at specific sites, and overlay plots are used to evaluate model performance. The IMPROVE sites chosen for the time series plots include the visibility-protected areas in Brigantine National Wildlife Refuge (NWR), NJ, Death Valley National Park (NP), CA, Swanqwarter National Wildlife Refuge (NWR), NC, and the Tallgrass Prairie National Preserve, KS. The Brigantine NWR is a tidal wetland and has a shallow bay, the Death Valley NP is a desert, and the Swanqwarter NWR is a coastal brackish marsh. The time series plots are made at four STN sites including two urban sites (in Washington, DC, and Boise, ID), one industrial site (in Tampa, FL), and one ru- ral/agricultural site (in Liberty, KS). SOA, hydroxyl radi- cal (OH), and hydroperoxy radical (HO 2 ) data are also avail-
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Secondary organic aerosol (SOA) formation from monoterpene ozonolysis in the presence of inorganic aerosols : acid effects on SOA yields

Secondary organic aerosol (SOA) formation from monoterpene ozonolysis in the presence of inorganic aerosols : acid effects on SOA yields

Beyond being able to model the fraction of oligomers formed due to the presence of inorganic aerosols, an experimental oligomer mass fraction estimation technique was developed using TGA which is targeted to bulk phase analysis of aerosols. The TGA method development study resulted in a new approach thermal analysis for aerosols. By subtracting the inorganic aerosol signal, the evolution of the particle phase organics with response to temperature increase is captured. The TGA study not only resulted in the development of a new analytical method, but also provide valuable information as to the how inorganics influence specific types of molecules. Under acidic conditions alcohols were found to only form organic sulfate, while pinonic acid which contains and a carboxylic acid group and a ketone was able to form a small amount of oligomer. Also the TGA study revealed a possible flaw in the use of organic carbon, elemental carbon (OC/EC) thermal analysis. OC/EC analysis is a thermally based analysis technique which heats sampled aerosols, and analyzes the evolved gases. Typically organic carbon is quantified at temperatures as high as 500ºC (Chow et al. 2004), and the charring of organics are assumed to occur in the presence of oxygen gas. The TGA study showed that at temperatures above 250ºC the oligomer fraction of the aerosol begins to decompose and form char. This char is quantified as EC in OC/EC analysis causing a possible underestimation of the OC fraction of aerosols.
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Primary to secondary organic aerosol: evolution of organic emissions from mobile combustion sources

Primary to secondary organic aerosol: evolution of organic emissions from mobile combustion sources

imum O : C ratio observed here is approximately 0.6, con- sistent with less-oxidized SV-OOA (Ng et al., 2010, 2011a). Further oxidative processing is required to produce more ox- idized LV-OOA (Ng et al., 2010, 2011a; Lambe et al., 2011). Translation of the AMS data into van Krevelen space (Fig. 9e) provides information concerning the oxidation chemistry in the gasoline and diesel experiments. The slopes for gasoline and diesel exhaust oxidation in van Krevelen space are −0.50 and −0.40. This suggests that SOA forma- tion chemistry is a combination of carboxylic acid and alco- hol/peroxide formation (Ng et al., 2011a; Heald et al., 2010), and is an indication that the photooxidation chemistry in the experiments presented here is atmospherically relevant. Am- bient OA data, when plotted in van Krevelen space, exhibit slopes between − 1 (Heald et al., 2010), indicative of chem- istry dominated by carboxylic acid formation, and − 0.5 (Ng et al., 2011a), indicative of chemistry dominated by a mixture of acid formation and alcohol/peroxide formation.
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Identifying Isoprene and Toluene Gas-Phase Oxidation Products to Better Constrain Ozone and Secondary Organic Aerosol Formation in the Atmosphere

Identifying Isoprene and Toluene Gas-Phase Oxidation Products to Better Constrain Ozone and Secondary Organic Aerosol Formation in the Atmosphere

creasing volatility. The atmospheric evolution that leads to SOA can be described in terms of the number of oxidation steps undergone, or the “generation number” of products formed. In an alternative route to SOA formation, low molecular weight, water-soluble VOCs can dissolve in droplets or particles wherein they undergo ox- idation to products that remain in the aqueous phase as dissolved SOA. When a droplet containing dissolved SOA eventually evaporates, a residual aerosol particle rich in oxidized organics remains. While experiments addressed at understanding aqueous-phase pathways to SOA formation have tended to employ “beaker scale” systems, studies with moist aerosols and in chambers are starting to emerge. In the absence of a seed aerosol, low volatility VOC oxidation products may accu- mulate in the chamber until a point is reached at which homogeneous nucleation of these products occurs. (The point at which nucleation occurs in a VOC system depends crucially on the VOC itself and the nature of its oxidation products.) Ex- periments carried out in the absence of a seed aerosol are useful for determining the density of the pure secondary organic aerosol, since the particles will consist exclusively of organic oxidation products. In the absence of a seed aerosol, the nucleated particles tend to concentrate in a range of relatively small particle sizes that may present measurement challenges. In addition, smaller sized particles are more prone to loss by deposition on the wall of the chamber than larger particles (see Section 2.6).
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Isoprene-derived secondary organic aerosol in the global aerosol–chemistry–climate model ECHAM6.3.0–HAM2.3–MOZ1.0

Isoprene-derived secondary organic aerosol in the global aerosol–chemistry–climate model ECHAM6.3.0–HAM2.3–MOZ1.0

3.2.4 Uncertainty estimation saturation vapor pressure As described in Sect. 2.1.1 the group contribution method by Nannoolal et al. (2008) in combination with the boiling point method by Nannoolal et al. (2004) were used to obtain the saturation vapor pressure of originated isoprene products as a function of temperature. Group contribution methods esti- mate the contribution of functional groups to saturation va- por pressure. The Nannoolal et al. (2008) group contribution method is based on 68 835 data points of 1663 components and just needs two inputs: the molecular structure and the normal boiling point. Nannoolal et al. (2008) report a good performance against measurements. Nevertheless, when its performance is compared to compounds outside the train- ing set, the results become worse (Barley and McFiggans, 2010; OMeara et al., 2014). Barley and McFiggans (2010) underline the fact that databases are typically biased towards mono-functional groups, and therefore group contribution methods trained with these data perform well for volatile fluids, but not for low-volatility compounds. OMeara et al. (2014) arrive at similar conclusions; they tested seven satura- tion vapor pressure estimation methods and found that even if the Nannoolal et al. (2008) method results in the lowest mean bias error, the method shows poor accuracy for com- pounds with low volatility. This tendency also holds true for the other tested methods, showing increasing error with an increasing number of hydrogen bonds. This systematic error results in an SOA formation overestimation.
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Governing policy processes and foresight

Governing policy processes and foresight

business trends can change quite radically even in the space of 10-15 years. 2 From a policy perspective, therefore, new methods are required, which can take into account uncertainty during a decision-preparatory process. Foresight is a prominent one from this point of view, for two reasons. First, it is capable of dealing with uncertainty by devising alternative (qualitatively, or fundamentally different) ‘futures’ (visions of future, future states or scenarios): Indeed, it is a distinctive feature of foresight to consider alternative futures. Second, foresight processes can reduce uncertainty, too, because participants can align their endeavours once they arrive at a shared vision. To this effect, however, it is a necessary condition to involve the major stakeholders, who can significantly influence the underlying trends by shaping the strategies or policies of their respective organisations (government agencies, businesses, research organisations, NGOs, unions, etc. – depending on the issues in question, as well as the political and decision-making culture of the ‘entity’ conducting a foresight programme: international organisations or regions, nation states, sub-national regions, business associations, groups or individual firms, cities, etc.)
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Biogas Production: The Fundamental Processes

Biogas Production: The Fundamental Processes

Anaerobic digestion is a technology that has long been used for the production of biogas. The technology is simple and tested and finds ready use in domestic and farming applications. The technology can contribute substantially to the sustainable energy recovery from organic waste particularly agriculture and municipal. The amount of agricultural and municipal organic wastes currently available for energy production is very large. Apart from significant energy source, it is important for comprehensive utilisation of biomass, agricultural, animal husbandry, forestry and fishery residues, thus controlling the pollution and protecting the environment. Waste management particularly in developing countries like Pakistan is one of the most serious environmental problems. The biogas technology provides two important benefits: environmentally safe waste management as well as the generation of clean renewable energy. Coordinating the factors like waste management, organic fertilizer, the biogas production and use may further optimize the promotion and
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Thermodynamic Modeling of Organic Aerosol

Thermodynamic Modeling of Organic Aerosol

We present a vapor pressure estimation method, based on quantum chemistry methods, to predict the liquid vapor pressure, enthalpies of vaporization, and heats of sublimation of atmospheric organic compounds. Predictions are compared to literature data, and the overall accuracy is considered satisfactory given the simplicity of the equations. Quantum mechanical methods were also used to investigate the thermodynamic feasibility of various acid-catalyzed aerosol-phase heterogeneous chemical reactions. A stepwise procedure is presented to determine physical properties such as heats of formation, standard entropies, Gibbs free energies of formation, and solvation energies from quantum mechanics, for various short-chain aldehydes and ketones. Equilibrium constants of hydration reactions and aldol condensation are then reported; predictions are in qualitatively agreement with previous studies. We have shown that quantum methods can serve as useful tools for first approximation, especially for species with no available data, in determining the thermodynamic properties of multifunctional oxygenates.
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The impact of biogenic, anthropogenic, and biomass burning volatile organic compound emissions on regional and seasonal variations in secondary organic aerosol

The impact of biogenic, anthropogenic, and biomass burning volatile organic compound emissions on regional and seasonal variations in secondary organic aerosol

uncertainties in deposition parameters. Including dry and wet deposition of SOA precursors will likely reduce SOA con- centrations. Another limitation to this study is the absence of aqueous SOA formation in aerosols (Ervens, 2015) and cloud water (McNeill et al., 2012). Further laboratory studies are required to provide detailed oxidation mechanisms of VOC species such that they can be implemented into chemistry– climate models. Future modelling work will evaluate dry de- position, wet deposition, and an evolving volatility distribu- tion or SOA precursors, and their impacts on SOA formation. Nevertheless, we have considered SOA formation from a number of different sources in a global composition- climate model, and compared against a consistent set of ob- servations. In doing so, we have highlighted that, overall the inclusion of new sources of SOA improves the ability of the UKCA model to simulate SOA distributions across many world regions. Additionally, the new estimate of the global SOA budget from UKCA lies within the range of estimates from other global modelling studies. Future modelling work should aim to improve confidence in SOA formation mech- anisms, and to explicitly simulate multigenerational oxida- tion products with evolving volatility. Furthermore, observa- tions of SOA are required in regions influenced by biogenic and biomass burning emissions, such as South America and Africa.
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Insights on the Formation and Fate of Organic Nitrates in the Atmosphere from Field and Laboratory Observations

Insights on the Formation and Fate of Organic Nitrates in the Atmosphere from Field and Laboratory Observations

In this study, the hydroxy nitrate branching ratios, α , are determined for a suite of alkenes. With this knowledge, we can estimate how much ozone (and, for terminal alkenes, how much formaldehyde) is produced for every alkyl nitrate formed. Recent research flights conducted over Houston as a part of the 2013 NASA SEAC4RS campaign provide an illustration of how measurements of hydroxy nitrates can be used to apportion the role of individual VOC precursors in oxidant formation. Previous field studies in the Houston–Galveston airshed have yielded contradictory conclusions on the causes for the high ozone episodes experienced in the region. TexAQS I (2000) indicated the direct emission of ethene, propene, butadiene, and butenes were associated with rapid ozone production (Daum et al., 2003; Ryerson et al., 2003; Wert et al., 2003; Zhang et al., 2004). Subsequently, however, data from TexAQS II (2005-6) indicated that primary or secondary emissions of formaldehyde and nitrous acid might contribute significantly to ozone production (Olaguer et al., 2009). Rappengluck et al. (2010) and Buzcu et al. (2011), for example, concluded that a quarter or more of the measured formaldehyde is directly emitted from ve- hicles. In contrast, Parrish et al. (2012) suggested that greater than 90 % of the formaldehyde is produced via alkene oxidation. The disagreement on the source of formaldehyde has significant implications for ozone mitigation strategies (Olaguer et al., 2014).
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