The airborne monitoring of bioaerosols has become a research area attracting significant scientific interest over the last few years because of potential impacts on human health. For example, so-called primary aerosol biological particles (PBAPs) such as pollen and fungal spores are known to induce allergic responses and therefore exacerbate reactions such as allergenic rhinitis (hay fever) and chronic obstructive pulmonary disease. Although impaction/optical microscopy has been used for many years to quantify airborne PBAPs, the use of fluorescence as an underpinning method to enable the development of online (“real-time”) instruments, such as the Waveband Integrated Bioaerosol Sensor (WIBS), is recent. In the current study, the conventional method of PBAPs sampling (automatic Hirst-type volumetric trap) was co-located with a WIBS-4 instrument at a campaign site in Cork, Ireland, close to its Harbour, for much of the month of July in 2010. The extensive data set thereby obtained represents important results to test the ability of the WIBS-4 approach to detect and quantify biological particles in the coarse to super-coarse size range (3–30 µm) at a location with semi-rural, semi-urban and coastal influences. Quantitative and qualitative comparisons were made between the different approaches. It is clear from the results obtained in this short field campaign performed in a relatively complex ambient air environment that the WIBS-4 instrument in low gain can provide very similar concentration patterns to those obtained by more traditional instrumentation used for the evaluation of fungal spore concentration levels. WIBS does, however, appear to overestimate particle concentrations in comparison with data obtained using the SporeWatch/optical microscopy approach. Interestingly, certain time periods in the campaign gave rise to contrasting fluorescence averages that correlated with the concentrations of certain fungal spore types monitored by the traditional impaction/optical microscopy approach. This phenomenon may be due to the differing biofluorophores available to differing spore types. The collection of real-time, early-warning signals of periods in which high releases of spores are occurring could prove to be beneficial in the construction of allergenic health warnings for the general public. This study should be considered as a proof of principle about the possibility of using light-induced fluorescence methods for fungal spore detection in ambient air.

A study has been performed that provides the first fluorescence lifetime results on the intrinsic fluorescence monitored for specific in situ biochemical components of individual pollen grains. The results obtained show that such measurements can provide a basis for analytical discrimination between a variety of airborne grass and tree pollen.

This study represents the first international intercomparison of fungal spore observations since 1990, focusing on atmospheric concentrations of Alternaria, Cladosporium, Ganoderma and Didymella spores. The campaigns were performed at sites located in Cork (Ireland) and Worcester (England) during summer 2010. Observations were made using Hirst-type volumetric spore traps and corresponding optical identification at the genus level by microscope. The measurements at both sites (including meteorological parameters) were compared and contrasted. The relationships between the fungal spore concentrations with selected meteorological parameters were investigated using statistical methods and multivariate regression trees (MRT). The results showed high correlations between the two sites with respect to daily variations. Statistically significant higher spore concentrations for Alternaria, Cladosporium and Ganoderma were monitored at the Worcester site. This result was most likely due to the differences in precipitation and local fungal spore sources at the two sites. Alternaria and Cladosporium reached their maxima a month earlier in Cork than in Worcester, and Didymella with Ganoderma peaked simultaneously with similar diurnal trends found for all the investigated spore types. MRT analysis helped to determine threshold values of the meteorological parameters that exerted most influence on the presence of spores: they were found to vary at the two sites. Our results suggest that the aeromycological profile is quite uniform over the British Isles, but a description of bioaerosols with respect to overall load and daily concentration can be quite diverse although the geographical difference between sites is relatively small. These variations in the concentrations therefore need to be explored at the national level.

Reflection–absorption infrared (RAIR) spectroscopy has been used to explore the low temperature condensed-phase photochemistry of atmospherically relevant organic nitrates for the first time. Three alkyl nitrates, methyl, isopropyl, and isobutyl nitrate together with a peroxyacyl nitrate, peroxyacetyl nitrate (PAN), were examined. For the alkyl nitrates, similar photolysis products were observed whether they were deposited neat to the gold substrate or codeposited with water. In addition to peaks associated with the formation of an aldehyde/ketone and NO, a peak near 2230 cm–1 was found to emerge in the RAIR spectra upon UV photolysis of the thin films. Together with evidence obtained by thermal programmed desorption (TPD), the peak is attributed to the formation of nitrous oxide, N2O, generated as a product during the photolysis. On the basis of the known gas-phase photochemistry for the alkyl nitrates, an intermediate pathway involving the formation of nitroxyl (HNO) is proposed to lead to the observed N2O photoproduct. For peroxyacetyl nitrate, CO2 was observed as a predominant product upon photolytic decomposition. In addition, RAIR absorptions attributable to the formation of methyl nitrate were also found to appear upon photolysis. By analogy to the known gas-phase and matrix-isolated-phase photochemistry of PAN, the formation of methyl nitrate is shown to likely result from the combination of alkoxy radicals and nitrogen dioxide generated inside the thin films during photolysis.

Both gaseous bromine and bromine chloride have been monitored in polar environments and implicated in the destruction of tropospheric ozone. The formation mechanisms operating for these halogen compounds have been suggested previously. However, few laboratory studies have been performed using environmentally relevant concentrations of bromide and chloride ions in polar ice mimics. In aqueous solutions held at room temperature, previous studies have shown that the major product is the Cl2Br¯ trihalide ion when solutions of bromate, hydrochloric acid, and bromide ions are left to equilibrate. In contrast, the results of the cryochemical experiments presented here suggest that the dibromochloride ion (BrBrCl¯) is the major product when solutions of bromate, sulfuric acid, bromide, and chloride ions are frozen. Such a species would preferentially release bromine to the gas phase. Hence, similar halide starting materials form structurally different trihalide ions when frozen, which are capable of releasing differing active halogens, BrCl and Br2, to the gas-phase. This is a potentially important finding because Br2 is photolyzed more readily and to longer wavelengths than BrCl and therefore the efficiency in forming products that can lead to ozone destruction in the atmosphere would be increased. Evidence is provided for the mechanism to occur by means of both the freeze-concentration effect and the incorporation of ions into the growing ice phase.

The low-temperature chemistry associated with environmentally available mercury has recently attracted considerable scientific interest due to the discovery of systemic gas-phase mercury depletion events (MDEs) which occur periodically at the poles. However, the fate of the mercury once it enters the snowpack is not fully understood, even its chemical speciation has yet to be well characterized. An issue that is of particular concern in frozen environments is the transformation of elemental mercury (Hg0) to more bioavailable oxidized forms, which can then be methylated by biotic and abiotic processes. The resulting methyl mercury species produced can bioaccumulate through the food chain and the health effects of this on humans and mammals have been well-documented. During the current study, a novel set of “freeze-induced” pathways, which can potentially affect the reactivity of dissolved gaseous mercury (DGM) were followed. The experiments were performed using environmentally relevant cosolutes at appropriate concentration levels and temperatures. Evidence is thereby presented that due to rate accelerations associated with the operation of the freeze-concentration effect, DGM is oxidized to Hg2+ ions when frozen in the presence of a variety of materials including hydrogen peroxide, nitrous acid and the sulfuric acid/O2 couple.

Acidic tropospheric aerosols contain inorganic species such as sulfurous acid (H2SO3). As the main alkaline species, ammonia (NH3) plays an important role in the heterogeneous neutralization of these acidic aerosols. An aerosol flow-tube apparatus was used to obtain simultaneous optical and size distribution measurements using FTIR and SMPS measurements, respectively, as a function of relative humidity and aerosol chemical composition. A novel chemiluminescence apparatus was also used to measure ammonium ion concentration [NH4+]. The interactions between ammonia and hydrated sulfur dioxide (SO2·H2O) were studied at different humidities and concentrations. SO2·H2O is an important species as it represents the first intermediate in the overall atmospheric oxidation process of sulfur dioxide to sulfuric acid (H2SO4). This complex was produced within gaseous, aqueous, and aerosol SO2 systems. The addition of ammonia gave mainly hydrogen sulfite (SHO3–) tautomers and disulfite ions (S2O52–). These species were prevalent at high humidities enhancing the aqueous nature of sulfur(IV) species. Their weak acidity is evident due to the low [NH4+] produced. Size distributions obtained correlated well with the various stages of particulate compositional development.

Reflection–absorption infrared spectroscopy (RAIRS) is used to explore the photochemistry of primary and tertiary alkyl nitrites deposited on a gold surface. The primary alkyl nitrites examined for this study were n-butyl, isobutyl, and isopentyl nitrite. These compounds showed qualitatively similar spectra to those observed in previous condensed-phase measurements. The photolysis of the primary nitrites involved the initial formation of an alkoxy radical and NO, followed by production of nitroxyl (HNO) and an aldehydic species. In addition, the formation of nitrous oxide, identified from its distinctive transition near 2230 cm–1, was observed to form from the self-reaction of nitroxyl. The reaction rates for cis and trans conformer decay, as tracked through their intense N═O stretching modes, were found to be significantly different, potentially due to a structural bias that favors HNO formation for the initial trans conformer photoproducts over recombination. Tert-butyl nitrite demonstrates only the trans conformer in the RAIRS spectra prior to photolysis; however, recombination of the initial NO and RO• photoproducts was observed to produce the cis conformer in the photolyzed samples. The primary photoproducts from tert-butyl nitrite can also react to form acetone and nitrosomethane, but the absence of HNO prohibits the formation of N2O that was observed for the primary alkyl nitrites. Additionally, the RAIRS spectrum of isobutyl nitrite co-deposited with water was measured to examine the photolysis of this species on a water–ice surface. No change in the identity of the photoproducts was observed in this experiment, and minimal frequency shifting (1–3 cm–1) of the vibrational modes occurred. In addition to being a known atmospheric source of NO and various aldehydes, our results point to cold surface processing of alkyl nitrites as a potential environmental source of nitrous oxide.

Atmospheric fine particulates act as prime vehicles for the transport of toxic chemicals into the human respiratory system on a daily basis and adverse human health effects do exist. By examining toxicological differences and chemical composition of ambient fine particles using a novel experimental design and chemometric approach, the present work examines the hypothesis: that it is not clear whether there are significant differences in public health risk from exposure to fine particles in a rural location compared to those in urban locations. In the present study, an investigation into the inorganic chemical characteristics and biological effects of PM2.5–0.1 on human lung epithelial cell line A549 has been performed. Biological responses were evaluated by in vitro tests using equivalent masses of PM2.5–0.1 samples, collected during different seasons at urban and rural locations in Cork, Ireland. The relationship between the biological responses and the chemical composition of the samples were investigated using Principal Component Analysis followed by Partial Least Squares regression analysis. The PM2.5–0.1 samples collected at three contrasting sites in Cork demonstrated the ability to generate reactive oxygen species upon exposure irrespective of season. However, the magnitude of generation was somewhat higher for samples collected in the urban sites, compared to those generated by rural samples. Similarly, metals such as Cu and Mn were found to be present in larger quantities in the urban-based composite samples compared to those for their rural counterparts. The induction of interleukin 6 determined in this study followed a very similar seasonal trend to the measured concentrations of potassium ions in the PM2.5–0.1 samples to which the A549 cells were exposed. The current study provides further support that identifying important chemical components and their sources, with subsequent targeted emission controls, which will likely prove to be a more cost-effective strategy for mitigating toxicity and protecting human health, than current approaches which depend on uncharacterized total particle mass, especially when sophisticated pattern recognition techniques are employed to assess limited airborne datasets.

A joint Fourier transform reflection absorption infrared spectroscopy/thermal programmed desorption (RAIRS/TPD) study has provided good evidence for the existence of protonated nitrosamide (NH3NO+) on surfaces at cold temperatures. This species has long been proposed to exist in studies of the DeNOx process and the decomposition of ammonium nitrite. In the context of the current experiments, performed at low-temperatures in the absence and presence of water-ice, the results provided a firm mechanistic basis for understanding the release of HONO from snowpack in a “dark” mechanism and also under alkaline surface conditions.

Interhalide ion formation resulting from the freezing of dilute solutions containing components found in natural sea salt are investigated as a potential mechanism for the release of interhalogens to the polar atmosphere. Acidified solutions containing iodide, bromide, and nitrite ions have been frozen and then thawed, with changes in speciation analyzed using UV−visible spectrophotometry. The freezing process is shown to induce the formation of the important interhalide ion, IBr2−. This species has previously been predicted to be a precursor of iodine monobromide, IBr, and represents a potentially important source of halogen atoms in the polar marine boundary layer. The reaction mechanisms that lead to the formation of IBr2− under freezing conditions are explored using both experimental and computational methodologies. The chemistry involved was subsequently modified in order to mimic naturally occurring conditions more closely and also incorporated the use of hydrogen peroxide as an oxidant. In contrast to previous studies, the freeze-induced production of IBr2− was thereby observed to occur up to pH <5.1, where the acidity levels are comparable to those found in the polar snowpack.

The detection and quantification of biological particles in the atmosphere is becoming an increasingly important field of study. One instrument designed for this purpose, known as WIBS-4, can measure individual particles and their number-size distributions in two pre-defined size ranges: (i) ∼0.3–12 μm and (ii) ∼3–31 μm (optical diameter, polystyrene latex equivalent) while also making measurements of fluorescence across two wavebands. It can also supply simultaneous information on particle asymmetry.Since particle number concentrations are provided by the technique, the counting efficiency of WIBS-4 needs to be defined. Therefore in the current study, a method for calibration suitable and necessary for use with single particle measuring instruments is described. The lower-end counting efficiency curve for the WIBS-4 was thereby defined in specific size regimes for the first time (D50∼0.489 μm and D100∼0.69 μm). Experiments were conducted at room temperature and atmospheric pressure using a range of different sized PolyStyrene Latex (PSL) microspheres. A TSI 3010 condensation particle counter, using butanol as a working fluid, was used as a reference particle counter. The results also demonstrated a relationship between fluorescence intensity and the calculated volume of the PSL particles, when λex=280 nm and λem∼310–400 nm. To our knowledge the current study represents the first to provide the fluorescence particle sensor community with both the counting efficiency of the WIBS-4 and a relationship plot giving a fluorescence intensity-particle size correlation over a broad PSL size range.

A study has been performed that provides the first fluorescence lifetime results on the intrinsic fluorescence monitored for specific in situ biochemical components of individual pollen grains. The results obtained show that such measurements can provide a basis for analytical discrimination between a variety of airborne grass and tree pollen.