Atmospheric Environment (v.43, #24)

Comparison of carbonyl compounds emissions from diesel engine fueled with biodiesel and diesel by Chao He; Yunshan Ge; Jianwei Tan; Kewei You; Xunkun Han; Junfang Wang; Qiuwen You; Asad Naeem Shah (3657-3661).
The characteristics of carbonyl compounds emissions were investigated on a direct injection, turbocharged diesel engine fueled with pure biodiesel derived from soybean oil. The gas-phase carbonyls were collected by 2,4-dinitrophenylhydrazine (DNPH)-coated silica cartridges from diluted exhaust and analyzed by HPLC with UV detector. A commercial standard mixture including 14 carbonyl compounds was used for quantitative analysis. The experimental results indicate that biodiesel-fueled engine almost has triple carbonyls emissions of diesel-fueled engine. The weighted carbonyls emission of 8-mode test cycle of biodiesel is 90.8 mg (kW h)−1 and that of diesel is 30.7 mg (kW h)−1. The formaldehyde is the most abundant compound of carbonyls for both biodiesel and diesel, taking part for 46.2% and 62.7% respectively. The next most significant compounds are acetaldehyde, acrolein and acetone for both fuels. The engine fueled with biodiesel emits a comparatively high content of propionaldehyde and methacrolein. Biodiesel, as an alternative fuel, has lower specific reactivity (SR) caused by carbonyls compared with diesel. When fueled with biodiesel, carbonyl compounds make more contribution to total hydrocarbon emission.
Keywords: Carbonyl compounds; Biodiesel; Diesel engine; Ozone-forming potential;

Product study of oleic acid ozonolysis as function of humidity by O. Vesna; M. Sax; M. Kalberer; A. Gaschen; M. Ammann (3662-3669).
The heterogeneous reaction of ozone with oleic acid (OA) aerosol particles was studied as function of humidity and reaction time in an aerosol flow reactor using an off-line gas chromatography mass spectrometry (GC–MS) technique. We report quantitative yields of the major C9 ozonolysis products in both gas and condensed phases and the effect of relative humidity on the product distribution. The measurements were carried out with OA aerosol particles at room temperature. The results indicate that the product yields are increasing with increasing relative humidity during the reaction. Nonanal (NN) was detected as the major gas-phase product (55.6 ± 2.3%), with 94.5 ± 2.4% of the NN yield in the gas, and 5.5 ± 2.7% in the particulate phase, whereas nonanoic, oxononanoic and azelaic acids were detected exclusively in the particulate phase. Using UV-spectrometry, we observed that peroxides make up the largest fraction of products, about half of the product aerosol mass, and their concentration decreased with increasing humidity.
Keywords: Oleic acid; Ozonolysis; Aerosol; Relative humidity;

MNEQA, an emissions model for photochemical simulations by S. Ortega; M.R. Soler; M. Alarcón; R. Arasa (3670-3681).
This study focuses on a new emissions model, Numerical Emissions Model for Air Quality (MNEQA), to be used in photochemical simulations and emission control strategies relating to tropospheric ozone pollutants. MNEQA processes available local information from external files and is easily adaptable to any desired spatial resolution. Top-down and bottom-up methodologies are combined to calculate emissions at the required resolution for photochemical simulations. It was used in conjunction with the MM5-CMAQ air quality modelling system and was applied to an episode of high ozone levels in June 2003. Emission results are widely analysed showing a difference of −8.8% with EMEP NOx emissions, and −18.7% with EMEP VOC emissions. Related to ozone simulations, comparative results between measurements and simulations indicated good behaviour of the model in reproducing diurnal ozone concentrations, as statistical values fall within the EPA and EU regulatory frameworks.
Keywords: Emissions model; Air quality; Tropospheric ozone; CMAQ; MM5;

The ventilation and pollutant transport in a two-dimensional (2D) street canyon of building-height-to-street-width (aspect) ratio h/b = 1 under different unstable stratifications were examined. To characterize the combined wind-buoyancy-driven flow and pollutant transport at different Richardson number Ri, a computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier–Stokes (RANS) equations with the Renormalization Group (RNG) k − ε turbulence model was adopted. Unlike the isothermal condition, a secondary recirculation is initiated at the ground-level windward corner of the street canyon once the unstable stratification is switched on (Ri < 0). It traps the ground-level pollutant leading to elevated pollutant concentration there. As Ri further decreases, the enlarging secondary recirculation enables direct pollutant removal from its core to the shear layer that offsets the ground-level pollutant accumulation. The ventilation and pollutant removal performance under different unstable stratifications are compared by the air (ACH) and pollutant (PCH) exchange rates, and pollutant retention time (τ). Both the mean and turbulent components of ACH are found to increase with decreasing Ri, suggesting that unstable stratification promotes ventilation in street canyons. Moreover, the CFD results agree well with our theoretical model that ACH2 varies linearly with Ri. Turbulent transport originally dominates the pollutant removal under isothermal condition. However, progressive domination of pollutant removal by mean wind can be observed with decreasing stability (decreasing Ri from 0 to −10.6). The critical value is estimated to be Ri = −8, below which mean wind is the major pollutant removal carrier. Reduction in τ is also observed with decreasing Ri. Hence, in unstable stratification, pollutant resides shorter time in the street canyon compared with its isothermal counterpart, and the ventilation and pollutant removal are more favorable.
Keywords: Air quality; Wind-buoyancy-driven flow; Computational fluid dynamics (CFD); k − ε turbulence model; Reynolds-averaged Navier–Stokes (RANS) equations; Street canyons;

It is well known that turbulent dispersion influences chemical reactions and that computation of reactant concentrations or mean chemical reaction rates can suffer of serious error when small-scale atmospheric processes' effects on chemical transformation are neglected. A quantity that gives a measure of the influence of turbulent dispersion on second-order chemical reaction rates is the intensity of segregation. A nonparametric estimator based on the kernel method aimed at measuring the intensity of segregation is proposed. Numerical benchmark tests, in the case of a Gaussian plume, are performed to study the suitability of this technique. The estimator works well, especially for small and moderate separation from the plume centreline and generally in the smooth parts of the estimated function. The effective reaction rate is computed and the percentage error emerges to be less than 5% in the best estimation intervals, and less than 40% in the worst. A method to reduce percentage error is introduced and improved performances are observed. The estimator proposed turns out to be particularly suitable for Lagrangian air quality modelling because it permits conservation of the grid independence.
Keywords: Chemically reactive plume; Mixing of chemical species; Intensity of segregation; Effective reaction rate; Kernel method;

Heterogeneous reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on particles by K. Miet; K. Le Menach; P.M. Flaud; H. Budzinski; E. Villenave (3699-3707).
This work deals with the kinetic study of the reactions of ozone with pyrene, 1-hydroxypyrene and 1-nitropyrene, adsorbed on model particles. Experiments were performed at room temperature and atmospheric pressure, using a quasi-static flow reactor in the absence of light. Compounds were extracted from particles using pressurized fluid extraction (PFE) and concentration measurements were performed using gas chromatography/mass spectrometry (GC/MS). The pseudo-first order rate constants were obtained from the fit of the experimental decay of particulate polycyclic compound concentrations versus reaction time. Experiments were performed at three different O3 concentrations from which second order rate constants were calculated. The following rate constant values were obtained at 293 K: k(O3 + Pyrene) = (3.2 ± 0.7) × 10−16 cm3 molecule−1 s−1; k(O3 + 1OHP) = (7.7 ± 1.4) ×10 −16 cm3 molecule−1 s−1; and k(O3 + 1NP) = (2.2 ± 0.5) × 10−17 cm3 molecule−1 s−1, for pyrene, 1-hydroxypyrene and 1-nitropyrene adsorbed on silica particles. The variation in the rate constants demonstrates the strong influence of the substituent (OH or NO2) on the heterogeneous reactivity of pyrene. The pyrene particulate concentration was also varied in order to check how this parameter may influence the experiments. Finally, oxidation products were investigated for all reactions and some were detected and identified for the first time for ozone heterogeneous reaction with pyrene adsorbed on particles.
Keywords: PAH; Pyrene; 1-Hydroxypyrene; 1-Nitropyrene; Silica particles; Ozone; Oxidation products; Kinetics;

Investigations of an intense aerosol loading during 2007 cyclone SIDR – A study using satellite data and ground measurements over Indian region by K.V.S. Badarinath; Shailesh Kumar Kharol; Anu Rani Sharma; V. Ramaswamy; D.G. Kaskaoutis; H.D. Kambezidis (3708-3716).
Tropical cyclones are prominent weather systems characterized by high atmospheric pressure gradients and wind speeds. Intense tropical cyclones occur in India during the pre-monsoon (spring), early monsoon (early summer), or post-monsoon (fall) periods. Originating in both the Bay of Bengal (BoB) and the Arabian Sea (AS), these tropical cyclones often attain velocities of more than 100 km h−1 and are notorious for causing intense rain and storm surge as they cross the Indian coast. In this study, we examine the changes in the aerosol properties associated with an intense tropical cyclone “SIDR”, that occurred during 11–16 November 2007 over BoB. This cyclone, accompanied with very strong surface winds reaching 223 km h−1, caused extensive damage over Bangladesh. Ground-based measurements of Aerosol Optical Depth (AOD) in the neighboring urban environment of Hyderabad, India, showed significant variations due to changes in wind velocity and direction associated with the cyclone passage. The Terra-MODIS and AVHRR satellite images showed prevalence of dust particles mixed with emissions from anthropogenic sources and biomass-burning AS, while the aerosol loading over BoB was significantly lower. The positive values of Aerosol index (AI) obtained from the Ozone Monitoring Instrument (OMI) suggested the presence of an elevated aerosol layer over the West coast of India, AS and Thar Desert during and after the cyclone episode. Meteorological parameters from the MM5 mesoscale model were used to study the variations in winds associated with the cyclonic activity. Particulate matter loading over the region during the cyclone period increased by ∼45% with an accompanying decrease in columnar aerosol optical depth. The variations in Angstrom parameters suggested coarse-mode particle loading due to dust aerosols as observed in satellite data.
Keywords: Bay of Bengal; Tropical cyclone; Arabian sea; Remote sensing; Aerosol properties; India; Hyderabad;

Relative rate techniques were used to determine k(Cl + CF3CF=CFCF3) = (7.27 ± 0.88) × 10−12, k(Cl + CF3CF2CF=CF2) = (1.79 ± 0.41) × 10−11, k(OH + CF3CF=CFCF3) = (4.82 ± 1.15) × 10−13, and k(OH + CF3CF2CF=CF2) = (1.94 ± 0.27) × 10−12 cm3 molecule−1 s−1 in 700 Torr of air or N2 diluent at 296 K. The chlorine atom- and OH radical-initiated oxidation of CF3CF=CFCF3 in 700 Torr of air gives CF3C(O)F in molar yields of 196 ± 11 and 218 ± 20%, respectively. Chlorine atom-initiated oxidation of CF3CF2CF=CF2 gives molar yields of 97 ± 9% CF3CF2C(O)F and 97 ± 9% COF2. OH radical-initiated oxidation of CF3CF2CF=CF2 gives molar yields of 110 ± 15% CF3CF2C(O)F and 99 ± 8% COF2. The atmospheric fate of CF3CF2C(O)F and CF3C(O)F is hydrolysis to give CF3CF2C(O)OH and CF3C(O)OH. The atmospheric lifetimes of CF3CF=CFCF3 and CF3CF2CF=CF2 are determined by reaction with OH radicals and are approximately 24 and 6 days, respectively. The contribution of CF3CF=CFCF3 and CF3CF2CF=CF2 to radiative forcing of climate change will be negligible.
Keywords: Fluorinated alkene; Atmospheric oxidation; Radiative efficiency; Perfluorocarboxylic acid;

Fungal spore fragmentation as a function of airflow rates and fungal generation methods by Hussein Kanaani; Megan Hargreaves; Zoran Ristovski; Lidia Morawska (3725-3735).
The aim of this study was to characterise and quantify the fungal fragment propagules derived and released from several fungal species (Penicillium, Aspergillus niger and Cladosporium cladosporioides) using different generation methods and different air velocities over the colonies. Real time fungal spore fragmentation was investigated using an Ultraviolet Aerodynamic Particle Sizer (UVASP) and a Scanning Mobility Particle Sizer (SMPS). The study showed that there were significant differences (p < 0.01) in the fragmentation percentage between different air velocities for the three generation methods, namely the direct, the fan and the fungal spore source strength tester (FSSST) methods. The percentage of fragmentation also proved to be dependent on fungal species. The study found that there was no fragmentation for any of the fungal species at an air velocity ≤0.4 m s−1 for any method of generation. Fluorescent signals, as well as mathematical determination also showed that the fungal fragments were derived from spores. Correlation analysis showed that the number of released fragments measured by the UVAPS under controlled conditions can be predicted on the basis of the number of spores, for Penicillium and A. niger, but not for C. cladosporioides. The fluorescence percentage of fragment samples was found to be significantly different to that of non-fragment samples (p < 0.0001) and the fragment sample fluorescence was always less than that of the non-fragment samples. Size distribution and concentration of fungal fragment particles were investigated qualitatively and quantitatively, by both UVAPS and SMPS, and it was found that the UVAPS was more sensitive than the SMPS for measuring small sample concentrations, whilethe results obtained from the UVAPS and SMAS were not identical for the same samples.
Keywords: Fungal spores; Fragments; Air velocity; Fluorescent percentage;

Carbonyl atmospheric reaction products of aromatic hydrocarbons in ambient air by Genevieve Obermeyer; Sara M. Aschmann; Roger Atkinson; Janet Arey (3736-3744).
To convert gaseous carbonyls to oximes during sampling, an XAD-4 resin denuder system pre-coated with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine and followed by analysis with methane positive chemical ionization gas chromatography/mass spectrometry was used to measure carbonyls in ambient air samples in Riverside, CA. In conjunction with similar analyses of environmental chamber OH radical-initiated reactions of o- and p-xylene, 1,2,4-trimethylbenzene, ethylbenzene, 4-hydroxy-2-butanone and 1,4-butanediol, we identified benzaldehyde, o-, m- and p-tolualdehyde and acetophenone and the dicarbonyls glyoxal, methylglyoxal, biacetyl, ethylglyoxal, 1,4-butenedial, 3-hexene-2,5-dione, 3-oxo-butanal, 1,4-butanedial and malonaldehyde in the ambient air samples. As discussed, these carbonyls and dicarbonyls can be formed from the OH radical-initiated reactions of aromatic hydrocarbons and other volatile organic compounds emitted into the atmosphere, and we conclude that in situ atmospheric formation is a major source of these carbonyls in our Riverside, CA, ambient air samples.
Keywords: Carbonyl compounds; Dicarbonyls; Aromatic hydrocarbons; Atmospheric reactions; Ambient air;

This work is a contribution to a large project, aimed at the development of an advanced environmental assessment modelling system to be used in Japan. The modelling system here considered consisted of the RAMS and HYPACT coupled models. The RAMS code was modified to properly simulate local scale phenomena using a fine mesh size of 250 m. In this direction, the main aim here was to investigate the effect of the choice of the turbulence closure scheme on the dispersion of pollutants. Our modified version of the RAMS/HYPACT model chain was validated using field experiments which were carried out by the Japan Atomic Energy Research Institute (JAERI) in the area of Mt. Tsukuba (Japan). The mean flow, turbulence and concentration fields obtained using two alternative turbulence closure schemes are compared. A discussion on the different performances of the turbulence closures is presented and the influence of the closure schemes over the plume dispersion is investigated.
Keywords: Turbulence closures; Mesoscale models; Dispersion models; Non-homogenous conditions; Experimental campaign;

Formation of submicron sulfate and organic aerosols in the outflow from the urban region of the Pearl River Delta in China by R. Xiao; N. Takegawa; Y. Kondo; Y. Miyazaki; T. Miyakawa; M. Hu; M. Shao; L.M. Zeng; A. Hofzumahaus; F. Holland; K. Lu; N. Sugimoto; Y. Zhao; Y.H. Zhang (3754-3763).
Size-resolved chemical compositions of non-refractory submicron aerosols were measured using a quadrupole Aerodyne aerosol mass spectrometer at a rural site near Guangzhou in the Pearl River Delta (PRD) of China in the summer of 2006. Two cases characterized as the outflows from the PRD urban region with plumes of high SO2 concentration were investigated. The evolution of sulfate size distributions was observed on a timescale of several hours. Namely mass concentrations of sulfate in the condensation mode (with vacuum aerodynamic diameters (Dva ) < 300 nm) increased at a rate of about 0.17–0.37 ppbv h−1 during the daytime. This finding was consistent with the sulfuric acid production rates of about 0.17–0.3 ppbv h−1, as calculated from the observed gas-phase concentrations of OH (∼3.3 × 106–1.7 × 107 cm−3) and SO2 (∼3–21.2 ppbv). This implies that the growth of sulfate in the condensation mode was mainly due to gas-phase oxidation of SO2. The observed rapid increase was caused mainly by the concurrent high concentrations of OH and SO2 in the air mass. The evolution of the mass size distributions of m/z 44, a tracer for oxygenated organic aerosol (OOA), was very similar to that of sulfate. The mass loadings of m/z 44 were strongly correlated with those of sulfate (r 2 = 0.99) in the condensation mode, indicating that OOA might also be formed by the gas-phase oxidation of volatile organic compound (VOC) precursors. It is likely that sulfate and OOA were internally mixed throughout the whole size range in the air mass.
Keywords: Sulfate; Organic aerosol; Size distribution; Gas-phase oxidation; Outflow of the PRD urban region;

An analysis of continuous black carbon concentrations in proximity to an airport and major roadways by Robin E. Dodson; E. Andres Houseman; Barbara Morin; Jonathan I. Levy (3764-3773).
Black carbon (BC), a constituent of particulate matter, is emitted from multiple combustion sources, complicating determination of contributions from individual sources or source categories from monitoring data. In close proximity to an airport, this may include aircraft emissions, other emissions on the airport grounds, and nearby major roadways, and it would be valuable to determine the factors most strongly related to measured BC concentrations. In this study, continuous BC concentrations were measured at five monitoring sites in proximity to a small regional airport in Warwick, Rhode Island from July 2005 to August 2006. Regression was used to model the relative contributions of aircraft and related sources, using real-time flight activity (departures and arrivals) and meteorological data, including mixing height, wind speed and direction. The latter two were included as a nonparametric smooth spatial term using thin-plate splines applied to wind velocity vectors and fit in a linear mixed model framework. Standard errors were computed using a moving-block bootstrap to account for temporal autocorrelation. Results suggest significant positive associations between hourly departures and arrivals at the airport and BC concentrations within the community, with departures having a more substantial impact. Generalized Additive Models for wind speed and direction were consistent with significant contributions from the airport, major highway, and multiple local roads. Additionally, inverse mixing height, temperature, precipitation, and at one location relative humidity, were associated with BC concentrations. Median contribution estimates indicate that aircraft departures and arrivals (and other sources coincident in space and time) contribute to approximately 24–28% of the BC concentrations at the monitoring sites in the community. Our analysis demonstrated that a regression-based approach with detailed meteorological and source characterization can provide insights about source contributions, which could be used to devise control strategies or to provide monitor-based comparisons with source-specific atmospheric dispersion models.
Keywords: Generalized additive models; Source apportionment; Black carbon; Airport; Particulate matter;

Simulation of boundary layer trajectory dispersion sensitivity to soil moisture conditions: MM5 and Noah-based investigation by Arturo I. Quintanar; Rezaul Mahmood; Monica V. Motley; Jun Yan; John Loughrin; Nanh Lovanh (3774-3785).
In this study, the sensitivity of trajectory paths to anomalous soil moisture was analyzed during three different synoptic episodes in June 2006. The MM5 and Noah land surface models were used to simulate the response of the planetary boundary layer. The HYSPLIT model was used for trajectory analysis. It was found that the response in horizontal lower-level wind field was larger at regions where vertical wind velocity changes were also large. In addition, the sensitivity to soil moisture changes was significant and localized where convective activity was well developed and synoptic effects did not dominate. A non-local effect was felt over the rest of the domain where convection was not present since the model atmosphere reacted as a whole to compensate for induced changes in vertical velocity. This finding was supported by the fact that domain averaged vertical velocities changes were of the order of 0.2 cm s−1 or less at about 650 hPa and about 200 times smaller than modeled local vertical velocity changes. The largest change in horizontal wind field near the surface was found for weak synoptic events on June 11–12 and June 22–23 while the stronger synoptic event of June 17–18 showed smaller differences. These changes in wind field conditions impacted the transport and dispersion of pollutants. To quantify the sensitivity of air quality estimates to soil moisture uncertainty, we have used three well known measures of trajectory differences: the absolute horizontal transport deviation (AHTD), the relative horizontal transport deviation (RHTD) and the absolute vertical transport deviation (AVTD) for an ensemble of 98 trajectories departing from a region well within the computational domain. For the June 11–12 event it was found that for wet and dry soil moisture experiments, AHTD, RHTD, and AVGTD can reach values in the range 60–100 km, 10–20% and 500–900 m at 24 h run time, respectively. For the June 17–18 and June 22–23 events these values of trajectory differences were reduced more than half. These differences in behavior between time periods are largely attributed to the combined effects of synoptic forcing and the sensitivity of planetary boundary layer to soil moisture changes during well developed convection. The implication for air quality studies is that the soil moisture anomaly and related uncertainty in planetary boundary layer response needs to be incorporated in order to construct an ensemble of the most probable scenarios in which pollutants are released and transported throughout a given target region.
Keywords: MM5; HYSPLIT; Soil moisture; Wind trajectory; Air quality;

Atmospheric nitrogen fluxes at the Belgian coast: 2004–2006 by László Bencs; Agnieszka Krata; Benjamin Horemans; Anna J. Buczyńska; Alin C. Dirtu; Ana F.L. Godoi; Ricardo H.M. Godoi; Sanja Potgieter-Vermaak; René Van Grieken (3786-3798).
Daily and seasonal variations in dry and wet atmospheric nitrogen fluxes have been studied during four campaigns between 2004 and 2006 at a coastal site of the Southern North Sea at De Haan (Belgium) located at coordinates of 51.1723° N and 3.0369° E. Concentrations of inorganic N-compounds were determined in the gaseous phase, size-segregated aerosol (coarse, medium, and fine), and rainwater samples. Dissolved organic nitrogen (DON) was quantified in rainwater. The daily variations in N-fluxes of compounds were evaluated with air-mass backward trajectories, classified into the main air-masses arriving at the sampling site (i.e., continental, North Sea, and Atlantic/UK/Channel).The three, non-episodic campaigns showed broadly consistent fluxes, but during the late summer campaign exceptionally high episodic N-deposition was observed. The average dry and wet fluxes for non-episodic campaigns amounted to 2.6 and 4.0 mg N m−2  d−1, respectively, whereas during the episodic late summer period these fluxes were as high as 5.2 and 6.2 mg N m−2  d−1, respectively.Non-episodic seasons/campaigns experienced average aerosol fluxes of 0.9–1.4 mg N m−2  d−1. Generally, the contribution of aerosol NH4 + was more significant in the medium and fine particulate fractions than that of aerosol NO3 , whereas the latter contributed more in the coarse fraction, especially in continental air-masses. During the dry mid-summer campaign, the DON contributed considerably (∼15%) to the total N-budget.Exceptionally high episodic aerosol-N inputs have been observed for the late summer campaign, with especially high deposition rates of 3.6 and 2.9 mg N m−2  d−1 for Atlantic/UK/Channel and North Sea-continental (mixed) air-masses, respectively. During this pollution episode, the flux of NH4 + was dominating in each aerosol fraction/air-mass, except for coarse continental aerosols. High deposition of gaseous-N was also observed in this campaign with an average total N-flux of 2–2.5-times higher than in other campaigns.
Keywords: Gaseous; Aerosol; Wet nitrogen flux; Atmospheric deposition; Inorganic N-nutrients; Dissolved organic nitrogen; Coastal eutrophication; North Sea;

Under typical atmospheric conditions, sulfuric acid and water vapors are likely most important species in the nucleation of new aerosol particles. The main source of H2SO4 in the atmosphere is oxidation of SO2. Hence, an understanding of the subsequent chemical reactions followed by aerosol-particles formation is of fundamental importance. Here we analyze the results of laboratory experiments in Svensmark et al. (2007) in which (i) the formation of neutral aerosol particles was observed at reported sulfuric acid concentrations well below the range where the binary homogeneous nucleation in a mixture of H2SO4–H2O vapors could be important and (ii) an electron catalytic effect on particle nucleation was suggested as an explanation of the experimental results and as a potential source of aerosol-particles formation in the Earth's atmosphere. In the article we give an interpretation of these experimental data based on a known mechanism of the neutral particles formation via ion-induced nucleation followed by recombination of charged clusters. The main results of our investigation are the following: (i) the observed neutral particles were likely formed via the recombination of ion clusters; (ii) the phenomena of electron photodetachment from ion clusters under UV radiation was improbable in conditions of this experiment and likely unrealized for typical negative ion clusters found in the Earth's atmosphere. In total, these experiments and model investigations show that far more and specially directed laboratory experiments are needed to clarify the ways by which cosmic rays and solar radiation may link to the Earth's climate.
Keywords: Aerosol formation; Ion-induced nucleation; Ion–ion recombination;

New Directions: Where is the link between reactive indoor air chemistry and health effects? by Nicola Carslaw; Sarka Langer; Peder Wolkoff (3808-3809).