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The article presents study on the measurement of atmospheric aerosols suing high-resolution time-of-flight aerosol mass spectrometry. It mentions that the approach takes advantage of the spectrometer's ability to identify organic and inorganic components in atmospheric aerosols. It also demonstrates eddy covariance measurements of ammonium, which are dominated by deposition of ammonium sulphate.

The article presents a study on the performance of the Toronto Photo-Oxidation Tube (TPOT) and Potential Aerosol Mass (PAM) flow tube reactors to develop instrumental techniques for characterizing organic aerosol aging. The study states that theThe PAM system was designed with lower surface-area-to volume (SA/V) ratio to minimize wall effects, while, the TPOT studies heterogeneous aerosol chemistry. Based on results, the TPOT has narrower residence time distribution (RTD) compared to PAM.

The article discusses the Aerosol Collection Module (ACM) and its first applications with a Gas Chromatograph Mass Spectrometer, Flame Ionization Detector (GC/MS-FID) system in a quasi on-line analysis of particulate of a new aerosol collector. It notes on the development of a new technique for quasi on-line compound measurements of the organic aerosol particles. Moreover, the ACM matched to a GC/MS-FID is used to identify major instrumental characteristics of the ACM.

Detailed analysis of particle measurements in the Lower Fraser Valley of British Columbia has provided process-related explanations for the elevated PM2.5 observations. The meteorological conditions from 24–30 August contributed to the build-up of particles including concentrated layers aloft. During this period, seven PM2.5 peaks were “diagnosed” based upon their origin, age and/or processes. Of interest were the peaks in the late evening of 26 August (expected large secondary organic contribution), 29 August in the early afternoon (oldest particles during the period mixed with fresh combustion organics) and two peaks on 30 August. These latter two peaks showed elevated sulphate and were less than 3h apart. The first was related to heterogeneous production and the second homogeneous production and nucleation. The type of analysis presented in this paper helps to identify unique situations for more detailed process studies. Successful interpretation of the observed PM2.5 required detailed meteorological analyses and was only possible with hourly or better mass quantification and size-resolved chemical characterization of the particles plus vertical aerosol backscatter profiles from LIDAR. This demonstrates the value of co-locating these approaches in the study of the processes influencing tropospheric aerosols. [Copyright &y& Elsevier]

Chemical ionization (CI) atmospheric pressure interface mass spectrometry is a unique analytical technique for its low detection limits, softness to preserve molecular information, and selectivity for particular classes of species. Here, we present a fast polarity switching approach for highly sensitive online analysis of a wide range of trace species in complex samples using selective CI chemistries and high-resolution mass spectrometry. It is achieved by successfully coupling a multischeme chemical ionization inlet (MION) and an Orbitrap Fourier transform mass spectrometer. The capability to flexibly combine ionization chemistries from both polarities effectively extends the detectability compared to using only one ionization chemistry, as commonly used positive and negative reagent ions tend to be sensitive to different classes of species. We tested the performance of the MION-Orbitrap using reactive gaseous organic species generated by α-pinene ozonolysis in an environmental chamber and a standard mixture of 71 pesticides. Diethylammonium and nitrate are used as reagent ions in positive and negative polarities. We show that with a mass resolving power of 280,000, the MION-Orbitrap can switch and measure both polarities within 1 min, which is sufficiently fast and stable to follow the temporal evolution of reactive organic species and the thermal desorption profile of pesticides. We detected 23 of the 71 pesticides in the mixture using only nitrate as the reagent ion. Facilitated by polarity switching, we also detected 47 pesticides using diethylammonium, improving the total number of detected species to 59. For reactive organic species generated by α-pinene ozonolysis, we show that combining diethylammonium and nitrate addresses the need to measure oxygenated molecules in atmospheric environments with a wide range of oxidation states. These results indicate that the polarity switching MION-Orbitrap can promisingly serve as a versatile tool for the nontargeted chemical analysis of trace species in various applications.

Iodine oxoacids are recognised for their significant contribution to the formation of new particles in marine and polar atmospheres. Nevertheless, to incorporate the iodine oxoacid nucleation mechanism into global simulations, it is essential to comprehend how this mechanism varies under various atmospheric conditions. In this study, we combined measurements from the CLOUD (Cosmic Leaving OUtdoor Droplets) chamber at CERN and simulations with a kinetic model to investigate the impact of temperature, ionisation, and humidity on iodine oxoacid nucleation. Our findings reveal that ion-induced particle formation rates remain largely unaffected by changes in temperature. However, neutral particle formation rates experience a significant increase when the temperature drops from +10 °C to -10 °C. Running the kinetic model with varying ionisation rates demonstrates that the particle formation rate only increases with a higher ionisation rate when the iodic acid concentration exceeds 1.5 × 10 7 cm -3 , a concentration rarely reached in pristine marine atmospheres. Consequently, our simulations suggest that, despite higher ionisation rates, the charged cluster nucleation pathway of iodic acid is unlikely to be enhanced in the upper troposphere by higher ionisation rates. Instead, the neutral nucleation channel is likely to be the dominant channel in that region. Notably, the iodine oxoacid nucleation mechanism remains unaffected by changes in relative humidity from 2% to 80%. However, under unrealistically dry conditions (below 0.008% RH at +10 °C), iodine oxides (I 2 O 4 and I 2 O 5 ) significantly enhance formation rates. Therefore, we conclude that iodine oxoacid nucleation is the dominant nucleation mechanism for iodine nucleation in the marine and polar boundary layer atmosphere., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

The interaction between nitrogen monoxide (NO) and organic peroxy radicals (RO 2 ) greatly impacts the formation of highly oxygenated organic molecules (HOM), the key precursors of secondary organic aerosols. It has been thought that HOM production can be significantly suppressed by NO even at low concentrations. Here, we perform dedicated experiments focusing on HOM formation from monoterpenes at low NO concentrations (0 - 82 pptv). We demonstrate that such low NO can enhance HOM production by modulating the RO 2 loss and favoring the formation of alkoxy radicals that can continue to autoxidize through isomerization. These insights suggest that HOM yields from typical boreal forest emissions can vary between 2.5%-6.5%, and HOM formation will not be completely inhibited even at high NO concentrations. Our findings challenge the notion that NO monotonically reduces HOM yields by extending the knowledge of RO 2 -NO interactions to the low-NO regime. This represents a major advance towards an accurate assessment of HOM budgets, especially in low-NO environments, which prevails in the pre-industrial atmosphere, pristine areas, and the upper boundary layer., (© 2023. The Author(s).)

New particle formation (NPF) in the tropical free troposphere (FT) is a globally important source of cloud condensation nuclei, affecting cloud properties and climate. Oxidized organic molecules (OOMs) produced from biogenic volatile organic compounds are believed to contribute to aerosol formation in the tropical FT, but without direct chemical observations. We performed in situ molecular-level OOMs measurements at the Bolivian station Chacaltaya at 5240 m above sea level, on the western edge of Amazonia. For the first time, we demonstrate the presence of OOMs, mainly with 4-5 carbon atoms, in both gas-phase and particle-phase (in terms of mass contribution) measurements in tropical FT air from Amazonia. These observations, combined with air mass history analyses, indicate that the observed OOMs are linked to isoprene emitted from the rainforests hundreds of kilometers away. Based on particle-phase measurements, we find that these compounds can contribute to NPF, at least the growth of newly formed nanoparticles, in the tropical FT on a continental scale. Thus, our study is a fundamental and significant step in understanding the aerosol formation process in the tropical FT., (© The Author(s) 2023. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd.)

Organic aerosols, a major constituent of fine particulate mass in megacities, can be directly emitted or formed from secondary processing of biogenic and anthropogenic volatile organic compound emissions. The complexity of volatile organic compound emission sources, speciation and oxidation pathways leads to uncertainties in the key sources and chemistry leading to formation of organic aerosol in urban areas. Historically, online measurements of organic aerosol composition have been unable to resolve specific markers of volatile organic compound oxidation, while offline analysis of markers focus on a small proportion of organic aerosol and lack the time resolution to carry out detailed statistical analysis required to study the dynamic changes in aerosol sources and chemistry. Here we use data collected as part of the joint UK-China Air Pollution and Human Health (APHH-Beijing) collaboration during a field campaign in urban Beijing in the summer of 2017 alongside laboratory measurements of secondary organic aerosol from oxidation of key aromatic precursors (1,3,5-trimethyl benzene, 1,2,4-trimethyl benzene, propyl benzene, isopropyl benzene and 1-methyl naphthalene) to study the anthropogenic and biogenic contributions to organic aerosol. For the first time in Beijing, this study applies positive matrix factorisation to online measurements of organic aerosol composition from a time-of-flight iodide chemical ionisation mass spectrometer fitted with a filter inlet for gases and aerosols (FIGAERO-ToF-I-CIMS). This approach identifies the real-time variations in sources and oxidation processes influencing aerosol composition at a near-molecular level. We identify eight factors with distinct temporal variability, highlighting episodic differences in OA composition attributed to regional influences and in situ formation. These have average carbon numbers ranging from C 5 -C 9 and can be associated with oxidation of anthropogenic aromatic hydrocarbons alongside biogenic emissions of isoprene, α-pinene and sesquiterpenes.

Atmospheric gas-to-particle conversion is a crucial or even dominant contributor to haze formation in Chinese megacities in terms of aerosol number, surface area and mass. Based on our comprehensive observations in Beijing during 15 January 2018-31 March 2019, we are able to show that 80-90% of the aerosol mass (PM 2.5 ) was formed via atmospheric reactions during the haze days and over 65% of the number concentration of haze particles resulted from new particle formation (NPF). Furthermore, the haze formation was faster when the subsequent growth of newly formed particles was enhanced. Our findings suggest that in practice almost all present-day haze episodes originate from NPF, mainly since the direct emission of primary particles in Beijing has considerably decreased during recent years. We also show that reducing the subsequent growth rate of freshly formed particles by a factor of 3-5 would delay the buildup of haze episodes by 1-3 days. Actually, this delay would decrease the length of each haze episode, so that the number of annual haze days could be approximately halved. Such improvement in air quality can be achieved with targeted reduction of gas-phase precursors for NPF, mainly dimethyl amine and ammonia, and further reductions of SO 2 emissions. Furthermore, reduction of anthropogenic organic and inorganic precursor emissions would slow down the growth rate of newly-formed particles and consequently reduce the haze formation.

Reducing the amount of organic aerosol (OA) is crucial to mitigation of particulate pollution in China. We present time and air-origin dependent variations of OA markers and source contributions at a regionally urban background site in South China. The continental air contained primary OA markers indicative of source categories, such as levoglucosan, fatty acids, and oleic acid. Secondary OA (SOA) markers derived from isoprene and monoterpenes also exhibited higher concentrations in continental air, due to more emissions of their precursors from terrestrial ecosystems and facilitation of anthropogenic sulfate for monoterpenes SOA. The marine air and continental-marine mixed air had more abundant hydroxyl dicarboxylic acids (OHDCA), with anthropogenic unsaturated organics as potential precursors. However, OHDCA formation in continental air was likely attributable to both biogenic and anthropogenic precursors. The production efficiency of OHDCA was highest in marine air, related to the presence of sulfur dioxide and/or organic precursors in ship emissions. Regional biomass burning (BB) was identified as the largest contributor of OA in continental air, with contributions fluctuating from 8% to 74%. In contrast, anthropogenic SOA accounted for the highest fraction of OA in marine (37 ± 4%) and mixed air (31 ± 3%), overriding the contributions from BB. This study demonstrates the utility of molecular markers for discerning OA pollution sources in the offshore marine atmosphere, where continental and marine air pollutants interact and atmospheric oxidative capacity may be enhanced.

Atmospheric new-particle formation (NPF) affects climate by contributing to a large fraction of the cloud condensation nuclei (CCN). Highly oxygenated organic molecules (HOMs) drive the early particle growth and therefore substantially influence the survival of newly formed particles to CCN. Nitrogen oxide (NO x ) is known to suppress the NPF driven by HOMs, but the underlying mechanism remains largely unclear. Here, we examine the response of particle growth to the changes of HOM formation caused by NO x . We show that NO x suppresses particle growth in general, but the suppression is rather nonuniform and size dependent, which can be quantitatively explained by the shifted HOM volatility after adding NO x . By illustrating how NO x affects the early growth of new particles, a critical step of CCN formation, our results help provide a refined assessment of the potential climatic effects caused by the diverse changes of NO x level in forest regions around the globe., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

We use a real-time temperature-programmed desorption chemical-ionization mass spectrometer (FIGAERO-CIMS) to measure particle-phase composition and volatility of nucleated particles, studying pure α-pinene oxidation over a wide temperature range (-50 °C to +25 °C) in the CLOUD chamber at CERN. Highly oxygenated organic molecules are much more abundant in particles formed at higher temperatures, shifting the compounds toward higher O/C and lower intrinsic (300 K) volatility. We find that pure biogenic nucleation and growth depends only weakly on temperature. This is because the positive temperature dependence of degree of oxidation (and polarity) and the negative temperature dependence of volatility counteract each other. Unlike prior work that relied on estimated volatility, we directly measure volatility via calibrated temperature-programmed desorption. Our particle-phase measurements are consistent with gas-phase results and indicate that during new-particle formation from α-pinene oxidation, gas-phase chemistry directly determines the properties of materials in the condensed phase. We now have consistency between measured gas-phase product concentrations, product volatility, measured and modeled growth rates, and the particle composition over most temperatures found in the troposphere.

Formation of new aerosol particles from trace gases is a major source of cloud condensation nuclei (CCN) in the global atmosphere, with potentially large effects on cloud optical properties and Earth's radiative balance. Controlled laboratory experiments have resolved, in detail, the different nucleation pathways likely responsible for atmospheric new particle formation, yet very little is known from field studies about the molecular steps and compounds involved in different regions of the atmosphere. The scarcity of primary particle sources makes secondary aerosol formation particularly important in the Antarctic atmosphere. Here, we report on the observation of ion-induced nucleation of sulfuric acid and ammonia-a process experimentally investigated by the CERN CLOUD experiment-as a major source of secondary aerosol particles over coastal Antarctica. We further show that measured high sulfuric acid concentrations, exceeding 10 7 molecules cm -3 , are sufficient to explain the observed new particle growth rates. Our findings show that ion-induced nucleation is the dominant particle formation mechanism, implying that galactic cosmic radiation plays a key role in new particle formation in the pristine Antarctic atmosphere.

We evaluate the performance of a new chemical ionization source called Vocus, consisting of a discharge reagent-ion source and focusing ion-molecule reactor (FIMR) for use in proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF) measurements of volatile organic compounds (VOCs) in air. The reagent ion source uses a low-pressure discharge. The FIMR consists of a glass tube with a resistive coating, mounted inside a radio frequency (RF) quadrupole. The axial electric field is used to enhance ion collision energies and limit cluster ion formation. The RF field focuses ions to the central axis of the reactor and improves the detection efficiency of product ions. Ion trajectory calculations demonstrate the mass-dependent focusing of ions and enhancement of the ion collision energy by the RF field, in particular for the lighter ions. Product ion signals are increased by a factor of 10 when the RF field is applied (5000-18 000 cps ppbv -1 ), improving measurement precision and detection limits while operating at very similar reaction conditions as traditional PTR instruments. Because of the high water mixing ratio in the FIMR, we observe no dependence of the sensitivity on ambient sample humidity. In this work, the Vocus is interfaced to a TOF mass analyzer with a mass resolving power up to 12 000, which allows clear separation of isobaric ions, observed at nearly every nominal mass when measuring ambient air. Measurement response times are determined for a range of ketones with saturation vapor concentrations down to 5 × 10 4 μg m -3 and compare favorably with previously published results for a PTR-MS instrument.

Secondary organic aerosol (SOA) impact climate by scattering and absorbing radiation and contributing to cloud formation. SOA models are based on studies of simplified chemical systems that do not account for the chemical complexity in the atmosphere. This study investigated SOA formation from a mixture of real Scots pine (Pinus sylvestris) emissions including a variety of monoterpenes and sesquiterpenes. SOA generation was characterized from different combinations of volatile compounds as the plant emissions were altered with an herbivore stress treatment. During active herbivore feeding, monoterpene and sesquiterpene emissions increased, but SOA mass yields decreased after accounting for absorption effects. SOA mass yields were controlled by sesquiterpene emissions in healthy plants. In contrast, SOA mass yields from stressed plant emissions were controlled by the specific blend of monoterpene emissions. Conservative estimates using a box model approach showed a 1.5- to 2.3-fold aerosol enhancement when the terpene complexity was taken into account. This enhancement was relative to the commonly used model monoterpene, "α-pinene". These results suggest that simplifying terpene complexity in SOA models could lead to underpredictions in aerosol mass loading.

The formation of new atmospheric particles involves an initial step forming stable clusters less than a nanometre in size (<~1 nm), followed by growth into quasi-stable aerosol particles a few nanometres (~1-10 nm) and larger (>~10 nm). Although at times, the same species can be responsible for both processes, it is thought that more generally each step comprises differing chemical contributors. Here, we present a novel analysis of measurements from a unique multi-station ground-based observing system which reveals new insights into continental-scale patterns associated with new particle formation. Statistical cluster analysis of this unique 2-year multi-station dataset comprising size distribution and chemical composition reveals that across Europe, there are different major seasonal trends depending on geographical location, concomitant with diversity in nucleating species while it seems that the growth phase is dominated by organic aerosol formation. The diversity and seasonality of these events requires an advanced observing system to elucidate the key processes and species driving particle formation, along with detecting continental scale changes in aerosol formation into the future.

Organic compounds in the atmosphere vary widely in their molecular composition and chemical properties, so no single instrument can reasonably measure the entire range of ambient compounds. Over the past decade, a new generation of in situ, field-deployable mass spectrometers has dramatically improved our ability to detect, identify, and quantify these organic compounds, but no systematic approach has been developed to assess the extent to which currently available tools capture the entire space of chemical identity and properties that is expected in the atmosphere. Reduced-parameter frameworks that have been developed to describe atmospheric mixtures are exploited here to characterize the range of chemical properties accessed by a suite of instruments. Multiple chemical spaces (e.g. oxidation state of carbon vs. volatility, and oxygen number vs. carbon number) were populated with ions measured by several mass spectrometers, with gas- and particle-phase α-pinene oxidation products serving as the test mixture of organic compounds. Few gaps are observed in the coverage of the parameter spaces by the instruments employed in this work, though the full extent to which comprehensive measurement was achieved is difficult to assess due to uncertainty in the composition of the mixture. Overlaps between individual ions and regions in parameter space were identified, both between gas- and particle-phase measurements, and within each phase. These overlaps were conservatively found to account for little (<10%) of the measured mass. However, challenges in identifying overlaps and in accurately converting molecular formulas into chemical properties (such as volatility or reactivity) highlight a continued need to incorporate structural information into atmospheric measurements.

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.

Homogeneous nucleation and subsequent cluster growth leads to the formation of new aerosol particles in the atmosphere. The nucleation of sulfuric acid and organic vapours is thought to be responsible for the formation of new particles over continents, whereas iodine oxide vapours have been implicated in particle formation over coastal regions. The molecular clustering pathways that are involved in atmospheric particle formation have been elucidated in controlled laboratory studies of chemically simple systems, but direct molecular-level observations of nucleation in atmospheric field conditions that involve sulfuric acid, organic or iodine oxide vapours have yet to be reported. Here we present field data from Mace Head, Ireland, and supporting data from northern Greenland and Queen Maud Land, Antarctica, that enable us to identify the molecular steps involved in new particle formation in an iodine-rich, coastal atmospheric environment. We find that the formation and initial growth process is almost exclusively driven by iodine oxoacids and iodine oxide vapours, with average oxygen-to-iodine ratios of 2.4 found in the clusters. On the basis of this high ratio, together with the high concentrations of iodic acid (HIO 3 ) observed, we suggest that cluster formation primarily proceeds by sequential addition of HIO 3 , followed by intracluster restructuring to I 2 O 5 and recycling of water either in the atmosphere or on dehydration. Our study provides ambient atmospheric molecular-level observations of nucleation, supporting the previously suggested role of iodine-containing species in the formation of new aerosol particles, and identifies the key nucleating compound., Competing Interests: The authors declare no competing financial interests.

Wildfires are important contributors to atmospheric aerosols and a large source of emissions that impact regional air quality and global climate. In this study, the regional and nearfield influences of wildfire emissions on ambient aerosol concentration and chemical properties in the Pacific Northwest region of the United States were studied using real-time measurements from a fixed ground site located in Central Oregon at the Mt. Bachelor Observatory (∼2700 m a.s.l.) as well as near their sources using an aircraft. The regional characteristics of biomass burning aerosols were found to depend strongly on the modified combustion efficiency (MCE), an index of the combustion processes of a fire. Organic aerosol emissions had negative correlations with MCE, whereas the oxidation state of organic aerosol increased with MCE and plume aging. The relationships between the aerosol properties and MCE were consistent between fresh emissions (∼1 h old) and emissions sampled after atmospheric transport (6-45 h), suggesting that biomass burning organic aerosol concentration and chemical properties were strongly influenced by combustion processes at the source and conserved to a significant extent during regional transport. These results suggest that MCE can be a useful metric for describing aerosol properties of wildfire emissions and their impacts on regional air quality and global climate.

New particle formation (NPF) is the source of over half of the atmosphere's cloud condensation nuclei, thus influencing cloud properties and Earth's energy balance. Unlike in the planetary boundary layer, few observations of NPF in the free troposphere exist. We provide observational evidence that at high altitudes, NPF occurs mainly through condensation of highly oxygenated molecules (HOMs), in addition to taking place through sulfuric acid-ammonia nucleation. Neutral nucleation is more than 10 times faster than ion-induced nucleation, and growth rates are size-dependent. NPF is restricted to a time window of 1 to 2 days after contact of the air masses with the planetary boundary layer; this is related to the time needed for oxidation of organic compounds to form HOMs. These findings require improved NPF parameterization in atmospheric models., (Copyright © 2016, American Association for the Advancement of Science.)

Sulfuric acid is widely recognized as a very important substance driving atmospheric aerosol nucleation. Based on quantum chemical calculations it has been suggested that the quantitative detection of gas phase sulfuric acid (H 2 SO 4 ) by use of Chemical Ionization Mass Spectrometry (CIMS) could be biased in the presence of gas phase amines such as dimethylamine (DMA). An experiment (CLOUD7 campaign) was set up at the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber to investigate the quantitative detection of H 2 SO 4 in the presence of dimethylamine by CIMS at atmospherically relevant concentrations. For the first time in the CLOUD experiment, the monomer sulfuric acid concentration was measured by a CIMS and by two CI-APi-TOF (Chemical Ionization-Atmospheric Pressure interface-Time Of Flight) mass spectrometers. In addition, neutral sulfuric acid clusters were measured with the CI-APi-TOFs. The CLOUD7 measurements show that in the presence of dimethylamine (<5 to 70 pptv) the sulfuric acid monomer measured by the CIMS represents only a fraction of the total H 2 SO 4 , contained in the monomer and the clusters that is available for particle growth. Although it was found that the addition of dimethylamine dramatically changes the H 2 SO 4 cluster distribution compared to binary (H 2 SO 4 -H 2 O) conditions, the CIMS detection efficiency does not seem to depend substantially on whether an individual H 2 SO 4 monomer is clustered with a DMA molecule. The experimental observations are supported by numerical simulations based on A Self-contained Atmospheric chemistry coDe coupled with a molecular process model (Sulfuric Acid Water NUCleation) operated in the kinetic limit.

Gas-phase oxidation routes of biogenic emissions, mainly isoprene and monoterpenes, in the atmosphere are still the subject of intensive research with special attention being paid to the formation of aerosol constituents. This laboratory study shows that the most abundant monoterpenes (limonene and α-pinene) form highly oxidized RO2 radicals with up to 12 O atoms, along with related closed-shell products, within a few seconds after the initial attack of ozone or OH radicals. The overall process, an intramolecular ROO→QOOH reaction and subsequent O2 addition generating a next R'OO radical, is similar to the well-known autoxidation processes in the liquid phase (QOOH stands for a hydroperoxyalkyl radical). Field measurements show the relevance of this process to atmospheric chemistry. Thus, the well-known reaction principle of autoxidation is also applicable to the atmospheric gas-phase oxidation of hydrocarbons leading to extremely low-volatility products which contribute to organic aerosol mass and hence influence the aerosol-cloud-climate system., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The recent development in measurement techniques and theoretical understanding has enabled us to study atmospheric vapor, cluster and nanoparticle concentrations, dynamics, and their connection to atmospheric nucleation. Here we present a summary of the chemistry of atmospheric clustering, growing nanoparticles, and their precursors. In this work, we focus particularly on atmospheric gas-to-particle conversion and recent progress in its understanding.

In June 2010, the NOAA WP-3D aircraft conducted two survey flights around the Deepwater Horizon (DWH) oil spill. The Gulf oil spill resulted in an isolated source of secondary organic aerosol (SOA) precursors in a relatively clean environment. Measurements of aerosol composition and volatile organic species (VOCs) indicated formation of SOA from intermediate-volatility organic compounds (IVOCs) downwind of the oil spill (Science2011, 331, doi 10.1126/science.1200320). In an effort to better understand formation of SOA in this environment, we present mass spectral characteristics of SOA in the Gulf and of SOA formed in the laboratory from evaporated light crude oil. Compared to urban primary organic aerosol, high-mass-resolution analysis of the background-subtracted SOA spectra in the Gulf (for short, "Gulf SOA") showed higher contribution of C(x)H(y)O(+) relative to C(x)H(y)(+) fragments at the same nominal mass. In each transect downwind of the DWH spill site, a gradient in the degree of oxidation of the Gulf SOA was observed: more oxidized SOA (oxygen/carbon = O/C ∼0.4) was observed in the area impacted by fresher oil; less oxidized SOA (O/C ∼0.3), with contribution from fragments with a hydrocarbon backbone, was found in a broader region of more-aged surface oil. Furthermore, in the plumes originating from the more-aged oil, contribution of oxygenated fragments to SOA decreased with downwind distance. Despite differences between experimental conditions in the laboratory and the ambient environment, mass spectra of SOA formed from gas-phase oxidation of crude oil by OH radicals in a smog chamber and a flow tube reactor strongly resembled the mass spectra of Gulf SOA (r(2) > 0.94). Processes that led to the observed Gulf SOA characteristics are also likely to occur in polluted regions where VOCs and IVOCs are coemitted.

Atmospheric emissions of gas and particulate matter from a large ocean-going container vessel were sampled as it slowed and switched from high-sulfur to low-sulfur fuel as it transited into regulated coastal waters of California. Reduction in emission factors (EFs) of sulfur dioxide (SO₂), particulate matter, particulate sulfate and cloud condensation nuclei were substantial (≥ 90%). EFs for particulate organic matter decreased by 70%. Black carbon (BC) EFs were reduced by 41%. When the measured emission reductions, brought about by compliance with the California fuel quality regulation and participation in the vessel speed reduction (VSR) program, are placed in a broader context, warming from reductions in the indirect effect of SO₄ would dominate any radiative changes due to the emissions changes. Within regulated waters absolute emission reductions exceed 88% for almost all measured gas and particle phase species. The analysis presented provides direct estimations of the emissions reductions that can be realized by California fuel quality regulation and VSR program, in addition to providing new information relevant to potential health and climate impact of reduced fuel sulfur content, fuel quality and vessel speed reductions.

We use results from positive matrix factorization (PMF) analysis of 15 urban aerosol mass spectrometer (AMS) data sets to derive simple methods for estimating major organic aerosol (OA) component concentrations in real time. PMF analysis extracts mass spectral (MS) profiles and mass concentrations for key OA components such as hydrocarbon-like OA (HOA), oxygenated OA (OOA), low-volatility OOA (LV-OOA), semivolatile OOA (SV-OOA), and biomass burning OA (BBOA). The variability in the component MS across all sites is characterized and used to derive standard profiles for real-time estimation of component concentrations. Two methods for obtaining first-order estimates of the HOA and OOA mass concentrations are evaluated. The first approach is the tracer m/z method, in which the HOA and OOA concentrations are estimated from m/z 57 and m/z 44 as follows: HOA ∼ 13.4 × (C(57) - 0.1 × C(44)) and OOA ∼ 6.6 × C(44), where C(i) is the equivalent mass concentration of tracer ion m/z i. The second approach uses a chemical mass balance (CMB) method in which standard HOA and OOA profiles are used as a priori information for calculating their mass concentrations. The HOA and OOA mass concentrations obtained from the first-order estimates are evaluated by comparing with the corresponding PMF results for each site. Both methods reproduce the HOA and OOA concentrations to within ∼30% of the results from detailed PMF analysis at most sites, with the CMB method being slightly better. For hybrid CMB methods, we find that fixing the LV-OOA spectrum and not constraining the other spectra produces the best results.

Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

Oxidative processing (i.e., "aging") of organic aerosol particles in the troposphere affects their cloud condensation nuclei (CCN) activity, yet the chemical mechanisms remain poorly understood. In this study, oleic acid aerosol particles were reacted with ozone while particle chemical composition and CCN activity were simultaneously monitored. The CCN activated fraction at 0.66 +/- 0.06% supersaturation was zero for 200 nm mobility diameter particles exposed to 565 to 8320 ppmv O3 for less than 30 s. For greater exposure times, however, the particles became CCN active. The corresponding chemical change shown in the particle mass spectra was the oxidation of aldehyde groups to form carboxylic acid groups. Specifically, 9-oxononanoic acid was oxidized to azelaic acid, although the azelaic acid remained a minor component, comprising 3-5% of the mass in the CCN-inactive particles compared to 4-6% in the CCN-active particles. Similarly, the aldehyde groups of alpha-acyloxyalkylhydroperoxide (AAHP) products were also oxidized to carboxylic acid groups. On a mass basis, this conversion was at least as important as the increased azelaic acid yield. Analysis of our results with Köhler theory suggests that an increase in the water-soluble material brought about by the aldehyde-to-carboxylic acid conversion is an insufficient explanation for the increased CCN activity. An increased concentration of surface-active species, which decreases the surface tension of the aqueous droplet during activation, is an interpretation consistent with the chemical composition observations and Köhler theory. These results suggest that small changes in particle chemical composition caused by oxidation could increase the CCN activity of tropospheric aerosol particles during their atmospheric residence time.

The application of mass spectrometric techniques to the real-time measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between approximately 50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li+ ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described., ((c) 2007 Wiley Periodicals, Inc.)

The ozonolysis of mixed oleic-acid/stearic-acid (OL/SA) aerosol particles from 0/100 to 100/0 wt % composition is studied. The magnitude of the divergence of the particle beam inside an aerosol mass spectrometer shows that, in the concentration range 100/0 to 60/40, the mixed OL/SA particles are liquid prior to reaction. Upon ozonolysis, particles having compositions of 75/25 and 60/40 change shape, indicating that they have solidified during reaction. Transmission electron micrographs show that SA(s) forms needles. For particles having compositions of 75/25, 60/40, and greater SA content, the reaction kinetics exhibit an initial fast decay of OL for low O(3) exposure with no further loss of OL at higher O(3) exposures. For compositions from 50/50 to 10/90, the residual OL concentration remains at 28 +/- 2% of its initial value. The initial reactive uptake coefficient for O(3), as determined by OL loss, decreases linearly from 1.25 (+/-0.2) x 10(-3) to 0.60 (+/-0.15) x 10(-3) for composition changes of 100/0 to 60/40. At 50/50 composition, the uptake coefficient drops abruptly to 0.15 (+/-0.1) x 10(-3), and there are no further changes with increased SA content. These observations can be explained with a combination of three postulates: (1) Unreacted mixed particles remain as supersaturated liquids up to 60/40 composition, and the OL in this form rapidly reacts with O(3). (2) SA, as it solidifies, locks into its crystal structure a significant amount of OL, and this OL is completely inaccessible to O(3). (3) Accompanying crystallization, some stearic acid molecules connect as a filamentous network to form a semipermeable gel containing liquid OL but with a reduced uptake coefficient because of the decrease in molecular diffusivity in the gel. An individual particle of 50/50 to 90/10 is hypothesized as a combination of SA crystals having OL impurities (postulate 2) that are partially enveloped by an SA/OL gel (postulate 3) to explain (a) the abrupt drop in the uptake coefficient from 60/40 to 50/50 and (b) the residual OL content even after high ozone exposure. The results of this study, pointing out the important effects of particle phase, composition, and morphology on chemical reactivity, contribute to an improved understanding of the aging processes of atmospheric aerosol particles.

Guidance for the performance evaluation of three-dimensional air quality modeling systems for particulate matter and visibility is presented. Four levels are considered: operational, diagnostic, mechanistic, and probabilistic evaluations. First, a comprehensive model evaluation should be conducted in at least two distinct geographical locations and for several meteorological episodes. Next, streamlined evaluations can be conducted for other similar applications if the comprehensive evaluation is deemed satisfactory. In all cases, the operational evaluation alone is insufficient, and some diagnostic evaluation must always be carried out. Recommendations are provided for designing field measurement programs that can provide the data needed for such model performance evaluations.

Thermodynamic data are presented for hydrates of nitric acid: HNO(3).H(2)O, HNO(3).2H(2)O, HNO(3).3H(2)O, and a higher hydrate. Laboratory data indicate that nucleation and persistence of metastable HNO(3).2H(2)O may be favored in polar stratospheric clouds over the slightly more stable HNO(3).3H(2)O. Atmospheric observations indicate that some polar stratospheric clouds may be composed of HNO(3).2H(2)O and HNO(3).3H(2)O. Vapor transfer from HNO(3).2H(2)O to HNO(3).3H(2)O could be a key step in the sedimentation of HNO(3), which plays an important role in the depletion of polar ozone.

Gaseous molecular ions containing argon and perchlorethylene, Ar(n)(C(2)Cl(4))(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/C(2)Cl(4) mixture 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(C(2)Cl(4))(m) (+) ions have been suspected of interfering with collection of (37)Ar(+) ions produced by the (37)Cl(v,e(-))(37)Ar(+) 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.

Donors are crucial to any artificial insemination by donor (AID) programme but information about them is limited. This paper discusses the sources, characteristics and processing of semen donors.