Markus Kalberer

The effect of water on gas-particle partitioning of secondary organic aerosol: II. m-xylene and 1,3,5-trimethylbenzene photooxidation systems

An investigation of the effect of relative humidity on aerosol formation from m-xylene and 1,3,5-trimethylbenzene photooxidation is reported. Experiments were performed in the presence and absence of ammonium sulfate seed particles (both aqueous and dry) to ascertain the effect of partitioning of oxidation products into a strong electrolytic solution or onto dry crystalline seed particles. In marked contrast to the α-pinene/ozone system, the final measured secondary organic aerosol yield was unaffected by the presence of gas-phase or liquid-phase water at relative humidities (RH) up to 50%. The hygroscopic nature of the aerosol generated upon photooxidation of m-xylene and 1,3,5-trimethylbenzene was examined; the hygroscopicity of the aerosol at 85% RH for both parent organics increased with the extent of the reaction, indicating that the first-generation oxidation products undergo further oxidation. Limited identification of the gas- and aerosol-phase products of m-xylene and 1,3,5-trimethylbenzene photooxidation is reported. It is evident that a more complete molecular identification of aromatic photooxidation aerosol awaits analytical techniques not yet brought to bear on this problem.

Elemental Composition of HULIS in the Pearl River Delta Region, China: Results Inferred from Positive and Negative Electrospray High Resolution Mass Spectrometric Data

The HUmic-LIke Substances (HULIS) fraction isolated from aerosol samples collected at a rural location of the Pearl River Delta Region (PRD), China, during the harvest season was analyzed by both positive and negative mode electrospray ionization (ESI) coupled with an ultrahigh resolution mass spectrometer (UHRMS). With the remarkable resolving power and mass accuracy of ESI-UHRMS, thousands of elemental formulas were identified. Formulas detected in the positive (ESI+) and the negative (ESI-) mode complement each other due to differences in the ionization mechanism, and the use of both provides a more complete characterization of HULIS. Compounds composed of C, H, and O atoms were preferentially detected in ESI- by deprotonation, implying their acidic properties. Tandem MS and Kendrick Mass Defect analysis implies that carboxyl groups are abundant in the CHO compounds. This feature is similar to those of natural fulvic acids, but relatively smaller molecular weights are observed in the HULIS samples. A greater number of reduced nitrogen organic compounds were observed in the ESI+ compared to ESI-. Compounds with biomass burning origin including alkaloids, amino acids, and their derivatives are their probable constituents. Sulfur-containing species were dominantly detected in ESI-. The presence of sulfate fragments in the MS/MS spectra of these species and their high O/S ratios implies that they are mainly organosulfates. Organosulfates and nitrooxy-organosulfates were often the most intensive peaks in the ESI- spectra. They are believed to be products of reactive uptake of photooxidation products of reactive volatile organic compounds by acidic sulfate particles. The elemental compositions deduced from the UHRMS analysis confirm the conclusion from our previous study that biomass burning and SOA formation are both important sources of HULIS in the PRD region.

Combined Determination of the Chemical Composition and of Health Effects of Secondary Organic Aerosols: The POLYSOA Project

Epidemiological studies show a clear link between increased mortality and enhanced concentrations of ambient aerosols. The chemical and physical properties of aerosol particles causing these health effects remain unclear. A major fraction of the ambient aerosol particle mass is composed of secondary organic aerosol (SOA). Recent studies showed that a significant amount of SOA consists of high molecular weight compounds (oligomers), which are chemically not well characterized. Within the POLYSOA project a large variety of state-of-the-art analytical chemical methods were used to characterize the chemical composition of SOA particles with emphasis on the oligomeric mass fraction. Mass spectrometric results showed that SOA oligomers are highly oxidized compounds and that hydroperoxides are formed, which is consistent with NMR results. This high molecular weight fraction accounts for up to 23% of the total organic carbon in SOA particles. These well-characterized SOA particles were deposited on three lung cell culture systems (microdissected respiratory epithelia from porcine tracheae, the human bronchial epithelial cell line BEAS-2B, and porcine lung surface macrophages obtained by bronchoalveolar lavage) in a newly constructed particle deposition chamber with the goal to eventually identify particle components that are responsible for cell responses leading to adverse health effects. In addition, monolayers of the alveolar epithelial cell line A549 were used in an alveolar epithelial repair model. The lung cells were examined for morphological, biochemical, and physiological changes after exposure to SOA. Analyses of the lung cells after exposure to SOA are ongoing. First data give evidence for a moderate increase of necrotic cell death as measured by lactate dehydrogenase release and for effects on the alveolar epithelial wound repair mainly due to alterations of cell spreading and cell migration at the edge of the wound. Thus, these first results indicate that SOA, in concentrations comparable to environmental concentrations, may induce distinct effects in lung cells.

Organosulfates in Humic-like Substance Fraction Isolated from Aerosols at Seven Locations in East Asia: A Study by Ultra-High-Resolution Mass Spectrometry

Humic-like substances (HULIS) in ambient aerosols collected at seven locations in East Asia were analyzed using electrospray ionization (ESI) coupled with an ultra-high-resolution mass spectrometer (UHRMS). Locations included a 3 km high mountaintop site in Taiwan, rural, suburban, and urban locations in the Pearl River Delta (PRD), South China, and in Taiwan. Organosulfates (OS) in the HULIS fraction were tentatively identified through accurate mass measurements and MS/MS spectra interpretation. In the two mountaintop samples collected in regional background atmosphere, little OS were detected, while a few hundred OS formulas were identified in the six samples taken in Taiwan and PRD. Many of the OS ions were among the most intense peaks in the negative ESI-UHRMS spectra, and their elemental formulas were identical to OS derived from biogenic volatile organic compounds (BVOCs) (e.g., monoterpenes) that have been identified in chamber studies. With OS having less than 6 carbon atoms too hydrophilic to be effectively retained in the HULIS fraction, OS containing 10 carbon atoms were the most abundant, indicating monoterpenes as important precursors of OS in the HULIS fraction. Clear spatial variation in abundance of OS was found among different atmospheric environments, with enhanced coupling of BVOCs with anthropogenic acidic aerosols observed in the PRD samples over the Taiwan samples. The double bond equivalent (DBE) values indicate the majority of OS (>90%) in the HULIS fraction are aliphatic. The elemental compositions of OS compounds containing N atoms (defined as CHONS) indicate that they are probably nitrooxy OS. Some insights into OS formation mechanisms are also gained through examining the presence/absence of perceived reactant-product formula pairs in the mass spectra. The results suggest the dominant epoxide intermediate pathway for formation of OS compounds without N atoms (defined as CHOS) and confirm the more readily hydrolyzed characteristics of the --ONO₂ group than the --OSO₃ group. There is a lack of evidence for the epoxide pathway to account for the formation of OS in the CHONS subgroup.

On the NO2 + soot reaction in the atmosphere

Recent modeling studies have suggested that soot is a key component of tropospheric chemistry in remote regions, acting to reduce HNO3 to NO2 and possibly NO2 to NO. It may be expected then that soot also affects the chemistry of rural and urban areas, where soot concentrations are typically several orders of magnitude higher than in the remote troposphere. In order to test this assumption, a modeling study was conducted for typical urban and rural areas, with the same HNO3/NO2/soot chemistry proposed in the previous modeling studies of the remote troposphere. Unreasonable results were found (e.g., nearly total suppression of urban ozone, in contradiction to common observations), suggesting that the NO2/soot reaction was considerably overestimated in previous modeling studies. Therefore the NO2/soot chemistry was reconsidered. A new preliminary mechanism is suggested, based on recent laboratory studies of this reaction. Results show that the NO2/soot reaction does not notably affect the Ox-NOx-HOx chemistry of the lower continental troposphere, except maybe during nighttime in urban environments. A potential contribution of the NO2/soot interaction to HONO production is noted.

Convective boundary layer evolution to 4 km asl over High‐alpine terrain: Airborne lidar observations in the Alps

Mountain ranges have important influences on the structure and composition of the convective boundary layer (CBL) and free troposphere (FT). Evolution of the summer CBL, measured over the European Alps using airborne lidar, was clearly observed to attain a near-uniform height up to 4.2 km asl by early afternoon. A climatology of in-situ high-alpine aerosol measurements suggests that such substantial growth, corresponding to ∼ 0.3 of the mid-latitude tropopause height, often occurs during summer months. Subsequent nocturnal collapse of the CBL was estimated to result in the venting of ∼ 0.8 ± 0.3 (SO44) Gg day−1 into a FT residual layer, leeward of the Alps.

Cellular Responses after Exposure of Lung Cell Cultures to Secondary Organic Aerosol Particles

The scope of this work was to examine in vitro responses of lung cells to secondary organic aerosol (SOA) particles, under realistic ambient air and physiological conditions occurring when particles are inhaled by mammals, using a novel particle deposition chamber. The cell cultures included cell types that are representative for the inner surface of airways and alveoli and are the target cells for inhaled particles. The results demonstrate that an exposure to SOA at ambient-air concentrations of about 10(4) particles/cm(3) for 2 h leads to only moderate cellular responses. There is evidence for (i) cell type specific effects and for (ii) different effects of SOA originating from anthropogenic and biogenic precursors, i.e. 1,3,5-trimethylbenzene (TMB) and alpha-pinene, respectively. There was no indication for cytotoxic effects but for subtle changes in cellular functions that are essential for lung homeostasis. Decreased phagocytic activity was found in human macrophages exposed to SOA from alpha-pinene. Alveolar epithelial wound repair was affected by TMB-SOA exposure, mainly because of altered cell spreading and migration at the edge of the wound. In addition, cellular responses were found to correlate with particle number concentration, as interleukin-8 production was increased in pig explants exposed to TMB-SOA with high particle numbers.

Fluorescent lifetime imaging of atmospheric aerosols: a direct probe of aerosol viscosity

The viscosity of atmospheric aerosol particles affects a number of key physical and chemical particle properties, such as composition and reactivity. However, determination of the microscopic viscosity of aerosol particles is a non-trivial task. We report a new method of imaging viscosity in a variety of model aerosol systems, based on a fluorescence lifetime determination of viscosity-sensitive fluorophores termed molecular rotors. We report the viscosity changes associated with the relative humidity dependent hygroscopicity of NaCI and sucrose aerosols, as well as reaction dependent changes in viscosity during ozonolysis of oleic acid aerosols. The Fluorescence Lifetime Imaging Microscopy (FLIM) of molecular rotors shows great promise in understanding important fundamental aerosol properties, which can be both time-dependent and spatially variable through the aerosol particle.

Uptake of gaseous hydrogen peroxide by submicrometer titanium dioxide aerosol as a function of relative humidity.

Hydrogen peroxide (H(2)O(2)) is an important atmospheric oxidant that can serve as a sensitive indicator for HO(x) (OH + HO(2)) chemistry. We report the first direct experimental determination of the uptake coefficient for the heterogeneous reaction of gas-phase hydrogen peroxide (H(2)O(2)) with titanium dioxide (TiO(2)), an important component of atmospheric mineral dust aerosol particles. The kinetics of H(2)O(2) uptake on TiO(2) surfaces were investigated using an entrained aerosol flow tube (AFT) coupled with a chemical ionization mass spectrometer (CIMS). Uptake coefficients (gamma(H(2)O(2))) were measured as a function of relative humidity (RH) and ranged from 1.53 x 10(-3) at 15% RH to 5.04 x 10(-4) at 70% RH. The observed negative correlation of RH with gamma(H(2)O(2)) suggests that gaseous water competes with gaseous H(2)O(2) for adsorption sites on the TiO(2) surface. These results imply that water vapor plays a major role in the heterogeneous loss of H(2)O(2) to submicrometer TiO(2) aerosol. The results are compared with related experimental observations and assessed in terms of their potential impact on atmospheric modeling studies of mineral dust and its effect on the heterogeneous chemistry in the atmosphere.

Toxicity of aged gasoline exhaust particles to normal and diseased airway epithelia

Particulate matter (PM) pollution is a leading cause of premature death, particularly in those with pre-existing lung disease. A causative link between particle properties and adverse health effects remains unestablished mainly due to complex and variable physico-chemical PM parameters. Controlled laboratory experiments are required. Generating atmospherically realistic aerosols and performing cell-exposure studies at relevant particle-doses are challenging. Here we examine gasoline-exhaust particle toxicity from a Euro-5 passenger car in a uniquely realistic exposure scenario, combining a smog chamber simulating atmospheric ageing, an aerosol enrichment system varying particle number concentration independent of particle chemistry, and an aerosol deposition chamber physiologically delivering particles on air-liquid interface (ALI) cultures reproducing normal and susceptible health status. Gasoline-exhaust is an important PM source with largely unknown health effects. We investigated acute responses of fully-differentiated normal, distressed (antibiotics-treated) normal, and cystic fibrosis human bronchial epithelia (HBE), and a proliferating, single-cell type bronchial epithelial cell-line (BEAS-2B). We show that a single, short-term exposure to realistic doses of atmospherically-aged gasoline-exhaust particles impairs epithelial key-defence mechanisms, rendering it more vulnerable to subsequent hazards. We establish dose-response curves at realistic particle-concentration levels. Significant differences between cell models suggest the use of fully-differentiated HBE is most appropriate in future toxicity studies.