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Aerosols of biogenic and anthropogenic origin affect the total radiative forcing of global climate. Poor knowledge of the pre-industrial aerosol concentration and composition, in particular of particles formed directly in the atmosphere from gaseous precursors, constitutes a large uncertainty in the anthropogenic radiative forcing. Investigations of new particle formation at pre-industrial-like conditions can contribute to the reduction of this uncertainty. Here we present observations taken at the remote Nepal Climate Observatory Pyramid station at 5,079?m above sea level, a few kilometres from the summit of Everest. We show that up-valley winds funnel gaseous aerosol precursors to higher altitudes. During this transport, these are oxidized into compounds of very low volatility, which rapidly form a large number of aerosol particles. These are then transported into the free troposphere, which suggests that the whole Himalayan region may act as an ‘aerosol factory’ and contribute substantially to the free tropospheric aerosol population. Aerosol production in this region occurs mainly via organic precursors of biogenic origin with little evidence of the involvement of anthropogenic pollutants. This process is therefore likely to be essentially unchanged since the pre-industrial period, and may have been one of the major sources that contributes to the upper tropospheric aerosol population during that time.

Boreal forest acts as a carbon sink and contributes to the formation of secondary organic aerosols via emission of aerosol precursor compounds. However, these influences on the climate system are poorly quantified. Here we show direct observational evidence that aerosol emissions from the boreal forest biosphere influence warm cloud microphysics and cloud–aerosol interactions in a scale-dependent and highly dynamic manner. Analyses of in situ and ground-based remote-sensing observations from the SMEAR II station in Finland, conducted over eight months in 2014, reveal substantial increases in aerosol load over the forest one to three days after aerosol-poor marine air enters the forest environment. We find that these changes are consistent with secondary organic aerosol formation and, together with water-vapour emissions from evapotranspiration, are associated with changes in the radiative properties of warm, low-level clouds. The feedbacks between boreal forest emissions and aerosol–cloud interactions and the highly dynamic nature of these interactions in air transported over the forest over timescales of several days suggest boreal forests have the potential to mitigate climate change on a continental scale. Our findings suggest that even small changes in aerosol precursor emissions, whether due to changing climatic or anthropogenic factors, may substantially modify the radiative properties of clouds in moderately polluted environments.

A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary organic aerosol (SOA). Isoprene (IP) and monoterpenes (MT) are the most important precursors of SOA originating from forests. The climate impacts from OA are currently estimated through parameterizations of water uptake that drastically simplify the complexity of OA. We combine laboratory experiments, thermodynamic modeling, field observations, and climate modeling to (1) explain the molecular mechanisms behind RH‐dependent SOA water‐uptake with solubility and phase separation; (2) show that laboratory data on IP‐ and MT‐SOA hygroscopicity are representative of ambient data with corresponding OA source profiles; and (3) demonstrate the sensitivity of the modeled aerosol climate effect to assumed OA water affinity. We conclude that the commonly used single‐parameter hygroscopicity framework can introduce significant error when quantifying the climate effects of organic aerosol. The results highlight the need for better constraints on the overall global OA mass loadings and its molecular composition, including currently underexplored anthropogenic and marine OA sources. The interaction of airborne particulate matter (“aerosols”) with water is of critical importance for processes governing climate, precipitation, and public health. It also modulates the delivery and bioavailability of nutrients to terrestrial and oceanic ecosystems. We present a microphysical explanation to the humidity‐dependent water uptake behavior of organic aerosol, which challenges the highly simplified theoretical descriptions used in, e.g., present climate models. With the comprehensive analysis of laboratory data using molecular models, we explain the microphysical behavior of the aerosol over the range of humidity observed in the atmosphere, in a way that has never been done before. We also demonstrate the presence of these phenomena in the ambient atmosphere from data collected in the field. We further show, using two state‐of‐the‐art climate models, that misrepresenting the water affinity of atmospheric organic aerosol can lead to significant biases in the estimates of the anthropogenic influence on climate. Phase separation effects explain differences in water affinity of biogenic secondary organic aerosol (SOA) at subsaturation and supersaturationLaboratory data for monoterpene and isoprene SOA are representative of field observations with corresponding gas‐phase organic profilesImportance of organic aerosol‐water interactions for global climate is governed by highly uncertain organic aerosol budgets

In the atmosphere nighttime removal of volatile organic compounds is initiated to a large extent by reaction with the nitrate radical (NO3) forming organic nitrates which partition between gas and particulate phase. Here we show based on particle phase measurements performed at a suburban site in the Netherlands that organic nitrates contribute substantially to particulate nitrate and organic mass. Comparisons with a chemistry transport model indicate that most of the measured particulate organic nitrates are formed by NO3oxidation. Using aerosol composition data from three intensive observation periods at numerous measurement sites across Europe, we conclude that organic nitrates are a considerable fraction of fine particulate matter (PM1) at the continental scale. Organic nitrates represent 34% to 44% of measured submicron aerosol nitrate and are found at all urban and rural sites, implying a substantial potential of PM reduction by NOxemission control. Particulate organic nitrate is ubiquitous in EuropeThe 34 to 44 percent of fine particulate nitrate is organicNighttime chemistry is a dominant source of particulate organic nitrates

Environmental context Fine particles (aerosols) containing organic compounds are central players in two important environmental issues: aerosol-climate effects and human health effects (including mortality). Although organics constitute half or more of the total fine-particle mass, their chemistry is extremely complex; of critical importance is ongoing oxidation chemistry in both the gas phase and the particle phase. Here we present a method for representing that oxidation chemistry when the actual composition of the organics is not known and show that relatively slow oxidant uptake to particles plays a key role in the very existence of organic aerosols. Abstract Organic aerosols play a critical role in atmospheric chemistry, human health and climate. Their behaviour is complex. They consist of thousands of organic molecules in a rich, possibly highly viscous mixture that may or may not be in phase equilibrium with organic vapours. Because the aerosol is a mixture, compounds from all sources interact and thus influence each other. Finally, most ambient organic aerosols are highly oxidised, so the molecules are secondary products formed from primary emissions by oxidation chemistry and possibly non-oxidative association reactions in multiple phases, including gas-phase oxidation, aqueous oxidation, condensed (organic) phase reactions and heterogeneous interactions of all these phases. In spite of this complexity, we can make a strong existential statement about organic aerosol: They exist throughout the troposphere because heterogeneous oxidation by OH radicals is more than an order of magnitude slower than comparable gas-phase oxidation.

The second-order rate constant (k2) for the aqueous-phase reaction Cl2(aq) + OH^- → HOCl + Cl^- was determined by measuring the uptake of gas-phase chlorine into water in a bubble train flow reactor. In making these measurements, we avoided some of the difficulties encountered in earlier studies. Data were obtained at 275, 293, and 303 K, yielding k2 = (1.3 ± 0.5) × 10⁸ M^-1 s^-1, (6 ± 2) × 10⁸ M^-1 s^-1, and (8 ± 3) × 10⁸ M^-1 s^-1, respectively. The atmospheric relevance of the chlorine hydrolysis reaction is discussed.

We present here the first measurements of the infrared complex refractive indices for supercooled ternary solutions of H2SO4, HNO3, and H2O under stratospheric conditions. The data sets were retrieved directly from the infrared extinction spectra of laboratory-generated aerosols. Comparisons of these results with a previously reported empirical mixing rule model¹ reveal significant differences, which we trace to errors in the binary acid/water thin film refractive indices used in the model. In addition, the model does not properly account for the concentrations of ionic and neutral species in the ternary solutions. The experimentally determined optical constants reported here will be useful for determining polar stratospheric cloud aerosol properties from infrared spectroscopic remote sensing measurements.

Organic compounds are a significant component of tropospheric aerosols. In the present experiments, ethylene glycol was selected as a surrogate hydrophilic organic compound for a study of surface properties of organic liquid−aqueous solutions. The mass accommodation coefficient of gas-phase HCl and HBr on ethylene glycol−water surfaces has been measured as a function of water mole fraction (0−1) and temperature. The gas uptake studies were performed under liquid−vapor equilibrium conditions using a droplet train flow reactor. The mass accommodation coefficient (α) for HCl on pure ethylene glycol increases from about 0.40 ± 0.06 at 303 K to 0.79 ± 0.12 at 258 K. Such negative temperature dependence for α has been observed in studies of gas uptake by aqueous surfaces. The HBr mass accommodation coefficient on ethylene glycol is near unity independent of temperature in the range studied. The mass accommodation coefficient on the ethylene glycol−water solution is well represented by α = αH2OX(s)H2O + αEG(1 − X(s)H2O), where X(s)H2O is the water fractional surface coverage obtained via the surface tension of the solution and the subscripted α's are the mass accommodation coefficients on pure water and pure ethylene glycol. The D−H isotope exchange probability of DCl on the gas−liquid interface of ethylene glycol was also studied and was measured to be 1, implying that the thermal accommodation coefficient is also 1.

The probabilities that a water vapor molecule striking a liquid water surface will (1) thermally equilibrate with the liquid surface and (2) penetrate that surface and be incorporated into the bulk liquid are parameters of fundamental importance to both chemical physics and atmospheric science. Here we report values for these parameters as a function of temperature in the range of 258−280 K, measured with a droplet train flow reactor under conditions that circumvent difficulties encountered in earlier studies. The mass accommodation coefficient (α) of H2O(g) on water was determined by measuring the uptake of ¹⁷O labeled gas-phase water under near equilibrium conditions. The mass accommodation coefficient has a negative temperature dependence, with the magnitude ranging from 0.17 ± 0.03 at 280 K to 0.32 ± 0.04 at 258 K. The temperature dependence and the magnitude of α are consistent with the critical complex theory of mass accommodation, previously applied to the uptake of other gas-phase species by aqueous surfaces. Experiments with D2O(g) on liquid water show that D−H isotope exchange on the liquid surface proceeds with unit probability, independent of temperature. This result implies that the thermal accommodation coefficient of H2O(g) on liquid water is 1 in the temperature range studied.

The simultaneous uptake of gas-phase DMS−O3 mixtures by water as a function of temperature (274−300 K) was studied in a bubble train flow reactor. The uptake data yielded the second-order rate constant for the aqueous-phase reaction DMS + O3 → DMSO + O2. The reaction products were established with NMR analysis. The reaction rate constant k2 was measured at four temperatures:  274, 283, 293, and 300 K, yielding (5.1 ± 2.0) × 10⁸ M^-1 s^-1, (5.9 ± 2.0) × 10⁸ M^-1 s^-1, (8.6 ± 3.6) × 10⁸ M^-1 s^-1, and (11 ± 4.5) × 10⁸ M^-1 s^-1 respectively. It is noteworthy that the magnitude of the aqueous reaction rate constant exceeds the corresponding gas-phase rate by a factor of about 10⁶. The atmospheric importance of the aqueous-phase DMS/O3 reaction is discussed.

Recent evidence has shown that the mesospheric sodium nightglow, a chemiluminescent process which produces atomic sodium D-line radiation in the Earth's upper atmosphere, proceeds through the first excited (A ²Σ⁺) electronic state of NaO. The rate of D-line radiation production is proportional to the rate constant for the reaction of NaO(A ²Σ⁺) + O(³P) and its branching ratio to produce excited Na(²P) rather than ground-state Na(²S). The only previously published measurement of the NaO + O(³P) reaction rate and branching ratio was performed under slow flow conditions and almost certainly primarily represents the reaction of ground-state NaO (X ²Π). We present low-pressure measurements of the NaO + O reaction kinetics using an NaO source reaction known to produce NaO in the (A ²Σ⁺) state and determine the 290 K reaction rate constant to be (5.1 ± 1.8) × 10^-10 cm³ s^-1 and the branching ratio to produce Na(²P) to be 0.14 ± 0.04. New data on the termolecular rate coefficient for the reaction Na + O2 + He → NaO2 + He at 290 K are also presented.

The uptake of gas-phase SO2, H2S, and CO2 by aqueous solutions was studied as a function of pH and temperature using droplet train flow reactor and bubble train reactor apparatuses. All three atmospheric species react with H2O and OH^-, acidifying aqueous solutions. Studies yielded the reaction rates of SO2, H2S, and CO2 with OH^- and the mass accommodation coefficient (α) of SO2 on water as a function of temperature. The second-order aqueous-phase rate coefficients at 291 K for SO2, H2S and CO2 reaction with OH^- are (1.1 ± 0.2) × 10¹⁰, (1.7 ± 0.2) × 10⁹, and (4.0 ± 0.7) × 10³ M^-1 s^-1, respectively. As far as we can determine, the rate coefficients for SO2 and H2S have been determined here for the first time. At 291 K, for SO2, α = 0.175 ± 0.015, and as in previous studies, the temperature dependence of α is well represented by the relationship α /(1 − α) = exp(−ΔGobs/RT) with ΔHobs = −7.6 ± 0.6 kcal mol^-1 and ΔSobs = −29.2 ± 2.1 cal mol^-1 K^-1.

Uptake of gas-phase NO2 by water was studied in both the droplet train and bubble train flow reactors. Aqueous surface reaction of NO2(g), reported previously in the literature, is not substantiated by these studies. The uptake of NO2(g) is a function of Henry's law coefficient (HNO2) and the second-order NO2(aq)−NO2(aq) hydrolysis reaction rate coefficient (k2), in the form HNO2(k2)^1/2. The NO2(aq)−NO2(aq) hydrolysis rate coefficient is defined by:  −d[NO2(aq)]/dt = 2k2[NO2(aq)]². The coupled nature of the uptake makes it difficult to obtain reliable separate values for the two parameters H and k2. Literature values for these parameters vary by as much as a factor of 5. With the bubble train apparatus it was possible to separate clearly the effects of solubility and reaction on NO2 gas uptake. From these measurements and analysis of literature values, recommended values of these parameters at 293 K are HNO2 = (1.4 ± 0.2) × 10^-2 M atm^-1 and k2 = (3.0 ± 0.9) × 10⁷ M^-1 s^-1. At 276 K, our best estimates are HNO2 = 2.3 (+0.3−0.9) × 10^-2 M atm^-1 and k2 = (2.2 ± 0.6) × 10⁷ M^-1 s^-1.

The uptake of gas-phase ammonia by sulfuric acid surfaces was measured as a function of temperature (248−288 K), gas−liquid interaction time (2−15 ms), and acid concentration (20−70 wt % H2SO4) using a droplet train apparatus. The uptake coefficient increases as a function of acid concentration and reaches unity at about 55 wt % H2SO4. The increased NH3 uptake in acid solution is apparently due to reaction between NH3 and H⁺ at the gas−liquid interface. The results yielded parameters required to model the reaction of NH3 with H⁺ at the gas−liquid interface. These uptake experiments were expanded to include a detailed study of gas transport to a moving train of droplets. An analysis of previous sulfuric acid aerosol neutralization experiments shows that the uptake of ammonia by ternary NH3−H2SO4−H2O solutions is significantly lower than that by fresh binary H2SO4−H2O solutions. At typical tropospheric water and ammonia vapor concentrations, NH3 uptake coefficients need to be included in detailed microphysical models of sulfuric acid aerosols.

The uptake of gas-phase ammonia by aqueous surfaces was measured as a function of temperature, gas liquid interaction time, and pH in the range 0−13. Uptake measurements at low pH yielded values of the mass accommodation coefficient (α) as a function of temperature. The mass accommodation coefficient increases as the temperature decreases, from 0.08 at 290 K to 0.35 at 260 K. Time dependence of the uptake yielded values for the Henry's law constant. Uptake measurements at high pH indicate that an ammonia surface complex is formed at the interface. Codeposition studies in which an aqueous surface, initially at pH = 4, was simultaneously exposed to both gas-phase ammonia and SO2 were also performed. In such a codeposition experiment, the species entering the liquid neutralize each other and as a result the uptake of each species is enhanced. Modeling calculations indicate that the uptake of each species is in accord with bulk liquid-phase kinetics.

Frequency-dependent optical constants have been determined from the Fourier transform infrared spectra of laboratory-generated liquid sulfuric acid/water aerosols over a range of temperatures and compositions that are relevant to the upper troposphere and lower stratosphere of Earth. The compositions of the particles were determined in situ using a tunable diode laser to monitor equilibrium water vapor pressures. The infrared complex refractive indices of sulfuric acid are shown to be strongly dependent on temperature and composition, because of changes in the equilibrium between sulfate and bisulfate ions. Results from this study also have implications in understanding the temperature dependence of intermolecular interactions within ionic solutions. The database presented here is the most extensive yet available for the liquid solutions of sulfuric acid.

The gas-phase infrared spectrum of the A²Σ⁺ ← X²Π electronic transition of the NaO radical was observed for the first time utilizing tunable diode laser differential absorption spectroscopy; 109 lines were found within the region 2015−2095 cm^-1 and 45 lines within 2654−2696 cm^-1. The NaO radical was produced by reaction of sodium vapor with N2O in a fast flow tube and detected using an astigmatic Herriott multipass absorption cell combined with rapid sweep integration absorption signal processing. Simple kinetic studies were performed in order to differentiate the NaO radical features from precursor N2O lines. The NaO A²Σ⁺ ← X²Π vibronic band structure was modeled using ab initio calculations by Langhoff and co-workers; the simulated NaO band profile agrees reasonably well with that observed. A preliminary assignment of some observed lines and the resulting molecular constants are presented. Quantitative absorption strength measurements indicate that either absorption line strengths for this transition are significantly smaller than indicated by ab initio calculations or the Na + N2O reaction produces a significant fraction of NaO(A) state which resists collisional quenching under our experimental conditions.

Isotope exchange for deuterated gas-phase acetic acid and ethanol in contact with water (H2O) droplets was studied using a droplet train apparatus. In these experiments, the gas-phase species interacts with liquid droplets and the loss of the species is monitored. The loss of the species may be due to the entry of the molecules into the bulk or to a reaction of the species at the gas−liquid interface, in this case isotope exchange. Studies were conducted as a function of pH in the range 0−14, droplet temperature in the range 291−263 K and gas−liquid interaction time in the range 2−15 ms. For deuterated acetic acid the isotope exchange probability with water molecules at the interface is near unity. On the other hand, isotope exchange probability for ethanol with surface water molecules at pH 7 is much smaller, ranging from 0.033 at 263 K to 0.051 at 291 K. Ethanol isotope exchange is both acid and base catalyzed. The exchange probability therefore increases both toward low and high pH and levels off to a plateau at pH 2 and 12, respectively. The maximum value of the isotope exchange probability at the plateau is significantly less than 1. It ranges between 0.14 and 0.18 with no clear trend in temperature. Results are explained in terms of a kinetic model in which it is assumed that the surface-adsorbed ethanol molecules are distributed between two distinct forms:  a weakly adsorbed state and a partially solvated state. Only the partially solvated molecules can interact with the near-surface ions in the interior of the liquid. A finite rate of entering the partially solvated state is responsible for the observed plateaus in isotope exchange at high and low pH. Parameters describing the gas uptake and isotope exchange processes are examined using two models to describe the surface species:  surface nucleation and Gibbs surface excess.

Gaseous molecular ions containing argon and perchlorethylene, Arn(C2Cl4)m+in which n≥ 1-29 and m≥ 1-4, are produced by electron bombardment of van der Waals clusters formed by expanding an Ar/C2Cl4mixture through a supersonic nozzle. Previous attempts to observe such ions in a high-pressure mass spectrometer were not successful, as with many other (“bastard”) ions that similarly lack a stable chemically bound neutral parent molecule. This is probably due to dissociation induced by the large exoergicity from charge transfer between species that differ greatly in ionization potential. Use of van der Waals clusters as parent species avoids entirely the exoergicity problem and thus offers a general method to generate bastard ions. The Ar(C2Cl4)m+ions have been suspected of interfering with collection of 37Ar+ions produced by the 37Cl(v,e-)37Ar+reaction in the solar neutrino observatory. Although, as shown by our results, these ions are stable, they are unlikely to inhibit collection on the long time scale of the solar neutrino experiment.

The experimental determination of the mass accommodation coefficient of H2SO4 vapor on aqueous sulfuric acid and the gas-phase diffusion coefficient of H2SO4 vapor in N2/H2O at 303 K is reported. The measurements were carried out under laminar flow conditions in a coated wall tubular flow reactor coupled to a chemical ionization mass spectrometer for gas-phase detection. Wall loss rates of H2SO4 vapor, from which both the mass accommodation coefficient and the gas diffusion coefficient were determined, were measured as a function of total reactor pressure, water vapor concentration, and sulfuric acid vapor concentration. The observed wall loss rate coefficient depends linearly on the inverse of the total reactor pressure (0.54−10 Torr) and is independent of the aqueous sulfuric acid composition over the range 73−98 wt %, which was varied by the addition of water vapor. A kinetic model based on the additivity of kinetic resistances that couples gas-phase diffusion and mass accommodation to the measured H2SO4 vapor loss rate has been applied to the data. The model yields a lower limit of 0.43 with a best fit value of 0.65. The mass accommodation coefficient is independent of the liquid H2SO4/H2O composition over the range investigated. The gas-phase diffusion coefficient for H2SO4 vapor in N2/H2O (H2O mixing ratio ≤0.32) was determined to be 66.8 ± 1.1 Torr cm² s^-1. The resistance model agrees well with a more rigorous approximate solution to the full continuity equation describing mass transport and kinetics. The atmospheric implications of the reported results are discussed.

Frequency-dependent complex refractive indices have been determined from the aerosol infrared extinction spectra of laboratory-generated nitric acid dihydrate (NAD) particles. The spectra reported here were recorded at several temperatures (160, 180, and 190 K) over the mid-infrared region of the spectrum (700−4700 cm^-1). The optical constants retrieved from these spectra are overall in reasonable agreement with results from thin-film experiments conducted at 184 K, although there are significant differences in the intensities of several absorption bands located below 1500 cm^-1. We attribute these to the different methods used to make the samples in the two types of experiments and consider the substrate-free aerosol results to be unperturbed NAD. The temperature dependence of the NAD aerosol optical constants was found to be quite weak between 160 and 190 K, in contrast to the strong temperature dependence observed previously for the optical constants of water ice.

The gas-phase reaction of SO3 with H2O and the heterogeneous reaction of SO3 with H2O−H2SO4 surfaces have been studied in a fast flow reactor coupled to a chemical ionization mass spectrometer (CIMS) for species detection. The gas-phase reaction was studied under turbulent flow conditions over the pressure range from 100 to 760 Torr N2 and the temperature range from 283 to 370 K. The loss rate of SO3 was measured under pseudo-first-order conditions; it exhibits a second-order dependence on water vapor concentration and has a strong negative temperature dependence. The first-order rate coefficient for the SO3 loss by gas-phase reaction shows no significant pressure dependence and can be expressed as k^I(s^-1) = 3.90 × 10^-41 exp(6830.6/T)[H2O]² where [H2O] is in units of molecule cm^-3 and T is in Kelvin. The overall uncertainty of our experimentally determined rate coefficients is estimated to be ±20%. At sufficiently low SO3 concentrations (<10¹² molecule cm^-3) the rate coefficient is independent of the initial SO3 level, as expected for a gas-phase reaction mechanism involving one SO3 and two H2O molecules. However, at higher concentrations and lower temperatures, increased rate coefficients were observed, indicating a fast heterogeneous reaction after the onset of binary homogeneous nucleation of acid hydrate clusters leading to particle formation, which was verified by light-scattering experiments. The heterogeneous loss of SO3 to the reactor walls has also been investigated under low pressure (1.1−12.5 Torr) laminar flow conditions. The loss rate is highly dependent on the humidity of the surface. In the presence of excess water the reactive sticking coefficient approaches unity and the wall loss rate is gas diffusion limited; under dry conditions it approaches zero, as expected. The atmospheric implications of the homogeneous and heterogeneous SO3−water reaction are discussed.

Isoprene (2‐methyl‐1, 3‐butadiene) is a nonmethane volatile organic compound (VOC) with the largest global emission and high reactivity. The oxidation of isoprene is crucial to atmospheric photochemistry and contributes significantly to the global formation of secondary organic aerosol. Here, we conducted comprehensive observations in polluted megacities of Nanjing and Shanghai during summer of 2018. We identified multiple functionalized isoprene oxidation products, of which 72% and 88% of the total mole concentration were nitrogen‐containing species with the dominant compound being C5 dihydroxyl dinitrate (C5H10N2O8). We calculated the volatility using the group‐contribution method and estimated the particle‐phase concentration by equilibrium gas/particle partitioning. The results showed that the multifunctional products derived from isoprene oxidation can contribute to 2.6% of the total organic aerosol mass (0.28 ± 0.27 μg/m3), highlighting the potential importance of isoprene oxidation in polluted regions. Isoprene, as one of the most important precursors to form secondary organic aerosol (SOA) globally, has been extensively studied, most of which however focused in the pristine regions. In polluted urban areas, where isoprene would interact significantly with anthropogenic emissions, for example, NOx, the understanding of SOA formation potential of isoprene is rather controversial. Here, we used state‐of‐the‐art instruments to measure isoprene, highly functionalized intermediate compounds and organic aerosol simultaneously at two suburban sites in eastern China region and identify several tens of isoprene oxidation products with most of which identified as nitrogen‐containing species, confirming the significant interaction between the isoprene derived peroxy radicals and NOx. These multifunctional products are mostly semi‐volatile species and can contribute considerably to the observed SOA, highlighting an important role of biogenic volatile organic compounds oxidation on SOA formation under high‐NOx conditions, for example, anthropogenic emission dominant regions. Simultaneous measurements of volatile organic compounds, highly functionalized intermediate compounds and organic aerosol were conductedOrganic nitrates dominated the C4‐C5 functionalized isoprene oxidation products detected by NO3−CIMSMost of the identified isoprene oxidation products were categorized as SVOC and can contributed to secondary organic aerosol Simultaneous measurements of volatile organic compounds, highly functionalized intermediate compounds and organic aerosol were conducted Organic nitrates dominated the C4‐C5 functionalized isoprene oxidation products detected by NO3−CIMS Most of the identified isoprene oxidation products were categorized as SVOC and can contributed to secondary organic aerosol

Beams of Arm(H2O)2-,m=0 to 4, are passed through an electric field and separated with a quadrupole mass spectrometer. Form<=2 the signal disappears at 31±1 kV/cm. Form=3 and 4 and larger (H2O)n-(n?6) no field detachment is observed up to 40 kV/cm. The application of these results to the binding of excess electron in water clusters is discussed.

Submicron atmospheric aerosol samples were collected during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 campaign on four platforms: Chebogue Point (Nova Scotia, Canada), Appledore Island (Maine), the CIRPAS Twin Otter over Ohio, and the NOAA R/V Ronald H. Brownin the Gulf of Maine. Saturated aliphatic C‐C‐H, unsaturated aliphatic C=C−H, aromatic C=C−H, organosulfur C‐O‐S, carbonyl C=O, and organic hydroxyl C‐OH functional groups were measured by calibrated Fourier Transform Infrared (FTIR) spectroscopy at all four sampling platforms. The ratio of molar concentrations of carbonyl C=O to saturated aliphatic C‐C‐H groups was nearly constant at each sampling platform, with the Twin Otter samples having the lowest ratio at 0.1 and the three more coastal platforms having ratios of 0.4 and 0.5. Organic mass (OM) to organic carbon (OC) ratios follow similar trends for the four platforms, with the Twin Otter having the lowest ratio of 1.4 and the coastal platforms having slightly higher values typically between 1.5 and 1.6. Organosulfur compounds were occasionally observed. Collocated organic aerosol sampling with two Aerodyne aerosol mass spectrometers for OM, a Sunset Laboratory thermo‐optical analysis instrument for OC, and an ion chromatography‐particle into liquid sampler (IC‐PILS) for speciated carboxylic acids provided comparable results for most of the project, tracking the time series of FTIR OM, OC, and carbonyl groups, respectively, and showing simultaneous peaks of similar magnitude during most of the project. The FTIR/IC‐PILS comparison suggests that about 9% of the carbonyl groups found in submicron organic particles on the Twin Otter are typically associated with low molecular weight carboxylic acids.

We report the detection of a class of related oxygenated compounds by proton‐transfer‐reaction mass‐spectrometry (PTR‐MS) that have rarely or never been observed as a group using in situ instrumentation. Measurements were made as part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) 2004 in Chebogue Point, Nova Scotia. The detected class of compounds discussed here includes acetic acid, formaldehyde, acetaldehyde, tentatively identified formic acid and hydroxyacetone, and unidentified compounds detected at mass to charge ratios 85, 87, 99, 101, 113, 115, and 129. Typical concentrations were 800, 2500, 450, 700, 85, 25, 50, 50, 60, 35, 20, and 25 ppt, respectively. The uniqueness of this class of compounds is illustrated by showing they were poorly related to trace gases found in the US outflow, local pollution, primary biogenic emissions and other oxygenated compounds such as acetone, methanol, and MEK measured by other in situ instrumentation. On the other hand these oxidized volatile organic compounds were related to chemical species in aerosols and their abundance was high during nucleation events. Thus they likely are gas phase species that are formed in parallel to biogenic secondary organic aerosol production. We clearly show these compounds do not originate from local sources. We also show these compounds match the oxidation products of isoprene observed in smog chamber studies, and we therefore suggest they must be mainly produced by oxidation of biogenic precursor compounds.

Measurements were made on board the NOAA RV Ronald H. Brownduring the second New England Air Quality Study (NEAQS 2004) to determine the source of the aerosol in the region and how sources and aging processes affect submicrometer aerosol chemical composition and optical properties. Using the Lagrangian particle dispersion model FLEXPART in combination with gas phase tracer compounds, local (urban), regional (NE U.S. urban corridor of Washington, D.C.; New York; and Boston), and distant (midwest industries and North American forest fires) sources were identified. Submicrometer aerosol measured near the source region (Boston Harbor) had a molar equivalence ratio near one with respect to NH4+, NO3−, and SO4=, had a large mass fraction of particulate organic matter (POM) relative to SO4=, and had relatively unoxidized POM. As distance from the source region increased, the submicrometer aerosol measured in the marine boundary layer became more acidic and had a lower POM mass fraction, and the POM became more oxidized. The relative humidity dependence of light extinction reflected the change in aerosol composition being lower for the near‐source aerosol and higher for the more processed aerosol. A factor analysis performed on a combined data set of aerosol and gas phase parameters showed that the POM measured during the experiment was predominantly of secondary anthropogenic origin.

(200 μm diameter) is studied in a low‐pressure flow reactor over the range 268‐294 K. In all cases, the uptake coefficient increases with decreasing temperature.