Nonequilibrium atmospheric secondary organic aerosol formation and growth (original) (raw)
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Atmospheric Chemistry and Physics, 2009
The yields of organic nitrates and of secondary organic aerosol (SOA) particle formation were measured for the reaction NO 3 +β-pinene under dry and humid conditions in the atmosphere simulation chamber SAPHIR at Research Center Jülich. These experiments were conducted at low concentrations of NO 3 (NO 3 +N 2 O 5 <10 ppb) and βpinene (peak∼15 ppb), with no seed aerosol. SOA formation was observed to be prompt and substantial (∼50% mass yield under both dry conditions and at 60% RH), and highly correlated with organic nitrate formation. The observed gas/aerosol partitioning of organic nitrates can be simulated using an absorptive partitioning model to derive an estimated vapor pressure of the condensing nitrate species of p vap ∼5×10 −6 Torr (6.67×10 −4 Pa), which constrains speculation about the oxidation mechanism and chemical identity of the organic nitrate. Once formed the SOA in this system continues to evolve, resulting in measurable aerosol volume decrease with time. The observations of high aerosol yield from NO x -dependent oxidation of monoterpenes provide an example of a significant anthropogenic source of SOA from biogenic hydrocarbon precursors. Estimates of the NO 3 +βpinene SOA source strength for California and the globe indicate that NO 3 reactions with monoterpenes are likely an important source (0.5-8% of the global total) of organic aerosol on regional and global scales.
Temperature dependence of secondary organic aerosol yield from the ozonolysis of?-pinene
2006
The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pinene was studied in a flow reactor at 263-303 K and 1007 hPa. The observed SOA yields were of similar magnitude as predicted by a two-product model based on detailed gas phase chemistry , reaching maximum values of 5 0.22-0.39 at high particle mass concentrations. However, the measurement data exhibited significant deviations (up to 50%) from the predicted linear dependence on inverse temperature. When fitting the measurement data with a two-product model, we found that both the partitioning coefficients (K om,i ) and the stoichiometric yields (α i ) of the low-volatile and semi-volatile species vary with temperature. The results indicate 10 that not only the reaction product vapour pressures but also the relative contributions of different gas-phase or multiphase reaction channels are dependent on temperature. We suggest that the modelling of secondary organic aerosol formation in the atmosphere needs to take into account the effects of temperature on the pathways and kinetics of the involved chemical reactions as well as on the gas-particle partitioning of 15 the reaction products. 20 vegetation emit large amounts of biogenic volatile organic compounds (BVOCs) (500-1800 Tg C yr −1 ). Besides isoprene monoterpenes are the most abundant BVOCs, and with an emission rate of 10-50 Tg C yr −1 β-pinene is the second most important monoterpene (Wiedinmyer et al., 2004). Biogenic secondary organic aerosol (SOA) are formed from oxidation of BVOCs in the atmosphere by O 3 , OH and NO 3 radicals, Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion
Mass yields of secondary organic aerosols from the oxidation of α-pinene and real plant emissions
Atmospheric Chemistry and Physics, 2011
Biogenic volatile organic compounds (VOCs) are a significant source of global secondary organic aerosol (SOA); however, quantifying their aerosol forming potential remains a challenge. This study presents smog chamber laboratory work, focusing on SOA formation via oxidation of the emissions of two dominant tree species from bo-5 real forest area, Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies), by hydroxyl radical (OH) and ozone (O 3 ). Oxidation of α-pinene was also studied as a reference system. Tetramethylethylene (TME) and 2-butanol were added to control OH and O 3 levels, thereby allowing SOA formation events to be categorised as resulting from either OH-dominated or O 3 -initiated chemistry. SOA mass yields from α-pinene 10 are consistent with previous studies while the yields from the real plant emissions are generally lower than that from α-pinene, varying from 1.9% at an aerosol mass loading of 0.69 µg m −3 to 13.6% at 32.8 µg m −3 . Mass yields from oxidation of real plant emissions are subject to the interactive effects of the molecular structures of plant emissions and their reaction chemistry with OH and O 3 , which lead to variations in condensable 15 product volatility. SOA formation can be reproduced with a two-product gas-phase partitioning absorption model in spite of differences in the source of oxidant species and product volatility in the real plant emission experiments. Condensable products from OH-dominated chemistry showed a higher volatility than those from O 3 -initiated systems during aerosol growth stage. Particulate phase products became less volatile via 20 aging process which continued after input gas-phase oxidants had been completely consumed.
Physical chemistry chemical physics : PCCP, 2014
Understanding mechanisms of formation, growth and physical properties of secondary organic aerosol (SOA) is central to predicting impacts on visibility, health and climate. It has been known for many decades that the oxidation of monoterpenes by ozone in the gas phase readily forms particles. However, the species responsible for the initial nucleation and the subsequent growth are not well established. Recent studies point to high molecular weight highly oxygenated products with extremely low vapor pressures (ELVOC, extremely low volatility organic compounds) as being responsible for the initial nucleation, with more volatile species contributing to particle growth. We report here the results of studies of SOA formed in the ozonolysis of α-pinene in air at 297 ± 2 K using atmospheric solids analysis probe (ASAP) mass spectrometry, attenuated total reflectance (ATR) Fourier transform infrared spectrometry and proton transfer reaction (PTR) mass spectrometry. Smaller particles are sho...
Integrating phase and composition of secondary organic aerosol from the ozonolysis of α-pinene
Proceedings of the National Academy of Sciences, 2014
Significance The phase of atmospheric aerosol particles can have dramatic effects on reactivity, growth, oxidation, and water uptake. As such, it plays a critical role in every aspect of particle evolution. Despite this, our knowledge of the phase of secondary organic aerosol (SOA) and how it changes in relation to conditions during SOA formation, particle history, composition, relative humidity, and temperature remains poor. Recent laboratory experiments suggest that SOA, under certain circumstances, is best described as a semisolid or viscous tar. This work shows how phase/viscosity, water availability during SOA formation, and composition are interrelated and offers mechanistic insights into these relationships.
Aerosol formation and heterogeneous chemistry in the atmosphere
EPJ Web of Conferences, 2011
A general presentation of the Earth's atmosphere is provided, with the associated photochemical processes and oxidizing capacity. The article focuses on the atmospheric reactivity of Volatile Organic Compounds (VOCs) and the associated reaction products in the gas phase (ozone, oxygenated organic compounds, organic nitrates. . .) and in the particle phase, namely, the Secondary Organic Aerosols (SOA). The understanding of the processes leading to SOA formation is currently a "hot topic" because of: i) their high concentrations in the measured total organic matter, and ii) their potential important impacts on health and climate change. The initial theory of SOA formation was based on thermodynamic phase transfers of oxidized reaction products of VOCs, but it failed to explain the presence of high molecular weight (high-MW) compounds observed in SOA as well as a 1 to 2 orders of magnitude discrepancy between models and observations on the quantity of SOA. Therefore, different research investigations have been proposed such as heterogeneous and aqueous phase reactivity of organic compounds.
Particle mass yield in secondary organic aerosol formed by the dark ozonolysis of α-pinene
Atmospheric Chemistry and Physics, 2008
The yield of particle mass in secondary organic aerosol (SOA) formed by dark ozonolysis was measured for 0.3-22.8 ppbv of reacted α-pinene. Most experiments were conducted using a continuous-flow chamber, allowing nearly constant SOA concentration and chemical composition for several days. For comparison, some experiments were 5 also conducted in batch mode. Reaction conditions were 25
Aerosol formation and growth in atmospheric organic/NOχ systems—II. Aerosol dynamics
Atmospheric Environment. Part A. General Topics, 1992
Secondary atmospheric aerosols are formed by gas-to-particle conversion of condensible vapors produced by reactions of primary species such as organics, NOx, SO2, and NH3. The rates and mechanisms leading to organic aerosol formation are the least well understood aspect of secondary atmospheric aerosols. Gas-phase measurements of organics, NOx, 03, and measurements of particle formation and growth have been made in smog chamber experiments to determine the total aerosol yields of the photochemical oxidation of various organics. Measurements of size distribution dynamics reveal the competition between nucleation and condensation, allowing estimation of the physical properties of the aerosol formed and the likelihood that a particular organic forms aerosol in the atmosphere. A new scanning electrical mobility spectrometer (SEMS) was developed to monitor aerosol size distribution dynamics. The measurement of particle size distributions using electrical mobility has been significantly accelerated using a new mode of operating mobility instruments. Rather than changing the electric field in discrete steps to select particles in a given mobility range, the electric field is scanned continuously. The particles are classified in a time-varying electric field, but for an exponential ramp in the field strength, there remains a one-to-one correspondence between the time a particle enters the classifier and the time it leaves. By this method, complete scans of mobility with as many as 100 mobility measurements have been made in 30 seconds using a differential mobility classifier with a condensation nuclei counter as a detector. Outdoor smog chamber experiments have been performed to determine the aerosolforming potential of selected C7and Cg-hydrocarbons in sunlight-irradiated hydrocarbon-NOx mixtures. Measured aerosol size distributions were used to determine the rates of gasto-particle conversion and to study the effects of the addition of SO;? and/or NH3 on aerosol formation and growth. The average aerosol yields by mass for the hydrocarbons studied were: meth ylcyclohexane 9.2% 1-octene 4.2% toluene 18.6% n-oc tane ~0.00 1 % Addition of SO2 to the organic/NOx systems led to an early nucleation burst and subsequent rapid growth of the newly formed aerosols. In the presence of NH3, the gasto-particle conversion rate of the organic/NOx system was enhanced perhaps due to the formation of NH4N03 or the reaction of NH3 with carboxylic acids. Sustained particle formation was observed when both SO2 and NH3 were present, presumably a result of (NH&S04 formation. We have estimated the complexity of the 1-octene aerosol and identified 5-propyl furanone as a major component of the aerosol. Aerosol dynamics that were observed in the outdoor smog chamber experiments are simulated by numerical solution of the aerosol general dynamic equation. The vapor source generation rate was estimated directly from the experimental measurements assuming a single surrogate condensing species for each hydrocarbon studied. Sensitivity analysis of the simulated aerosol dynamics to various input parameters revealed that the physical properties of the condensing vapor are important in determining the interplay between nucleation and condensation while the vapor source generation rate is the only factor that determines the eventual total amount of vapor converted to aerosol. The simulations suggest that over 99% of the mass of condensible vapor is converted to aerosol by condensation even when a significant burst of nucleation occurs.
2021
The reaction of a-pinene with NO3 is an important sink of both a-pinene and NO3 at night in regions with mixed biogenic and anthropogenic emissions; however, there is debate on its importance for secondary organic aerosol (SOA) and reactive nitrogen budgets in the atmosphere. Previous experimental studies have generally observed low or zero SOA formation, often due to excessive [NO3] conditions. Here, we characterize the SOA and organic nitrogen formation from apinene + NO3 as a function of nitrooxy peroxy (nRO2) radical fates with HO2, NO, NO3, and RO2 in an atmospheric chamber. We show that SOA yields are not small when the nRO2 fate distribution in the chamber mimics that in the atmosphere, and the formation of pinene nitrooxy hydroperoxide (PNP) and related organonitrates in the ambient can be reproduced. Nearly all SOA from a-pinene + NO3 chemistry derives from the nRO2 + nRO2 pathway, which alone has an SOA mass yield of 65(±9)%. Molecular composition analysis shows that particulate nitrates are a large (60-70%) portion of the SOA, and that dimer formation is the primary mechanism of SOA production from a-pinene + NO3 under simulated nighttime conditions. We estimate an average nRO2 + nRO2 à ROOR branching ratio of ~18%. Synergistic dimerization between nRO2 and RO2 derived from ozonolysis and OH oxidation also contribute to SOA formation, and should be considered in models. We report a 58 (±20)% molar yield of PNP from the nRO2 + HO2 pathway. Applying these laboratory constraints to model simulations of summertime conditions observed in the Southeast United States (where 80% of a-pinene is lost via NO3 oxidation, leading to 20% nRO2 + nRO2 and 45% nRO2 + HO2) , we estimate yields of 13% SOA and 9% particulate nitrate by mass, and 26% PNP by mole, from a-pinene + NO3 in the ambient. These results suggest that a-pinene + NO3 significantly contributes to the SOA budget, and likely constitutes a major removal pathway of reactive nitrogen from the nighttime boundary layer in mixed biogenic/anthropogenic areas.