Single-particle speciation of alkylamines in ambient aerosol at five European sites.

Alkylamines are associated with both natural and anthropogenic sources and have been detected in ambient aerosol in a variety of environments. However, little is known about the ubiquity or relative abundance of these species in Europe. In this work, ambient single-particle mass spectra collected at five sampling sites across Europe have been analysed for their alkylamine content. The aerosol time-of-flight mass spectrometer (ATOFMS) data used were collected in Ireland (Cork), France (Paris, Dunkirk and Corsica) and Switzerland (Zurich) between 2008 and 2013. Each dataset was queried for mass spectral marker ions associated with the following ambient alkylamines: dimethylamine (DMA), trimethylamine (TMA), diethylamine (DEA), triethylamine (TEA), dipropylamine (DPA) and tripropylamine (TPA). The fraction of ambient particles that contained detectable alkylamines ranged from 1 to 17 % depending on location, with the highest fractions observed in Paris and Zurich in the winter months. The lowest fractions were observed at coastal sites, where the influence of animal husbandry-related alkylamine emissions is also expected to be lowest. TMA was the most ubiquitous particle phase alkylamine detected and was observed at all locations. Alkylamines were found to be internally mixed with both sulphate and nitrate for each dataset, suggesting that aminium salt formation may be important at all sites investigated. Interestingly, in Corsica, all alkylamine particles detected were also found to be internally mixed with methanesulphonic acid (MSA), indicating that aminium methanesulphonate salts may represent a component of marine ambient aerosol in the summer months. Internal mixing of alkylamines with sea salt was not observed, however. Alkylamine-containing particle composition was found to be reasonably homogeneous at each location, with the exception of the Corsica and Dunkirk sites, where two and four distinct mixing states were observed, respectively.

The effect of freezing on reactions with environmental impact.

The knowledge that the freezing process can accelerate certain chemical reactions has been available since the 1960s, particularly in relation to the food industry. However, investigations into such effects on environmentally relevant reactions have only been carried out since the late 1980s. Some 20 years later, the field has matured and scientists have conducted research into various important processes such as the oxidation of nitrite ions to nitrates, sulfites to sulfates, and elemental mercury to inorganic mercury. Field observations mainly carried out in the polar regions have driven this work. For example, researchers have found that both ozone and mercury are removed from the troposphere completely (and almost instantaneously) at the time of Arctic polar sunrise. The monitoring activities suggested that both the phenomena were caused by involvement of bromine (and possibly iodine) chemistry. Scientists investigating the production of interhalide products (bromine and iodine producing interhalides) in frozen aqueous solutions have found that these reactions result in both rate accelerations and unexpected products. Furthermore, these scientists did this research with environmentally relevant concentrations of reagents, thereby suggesting that these reactions could occur in the polar regions. The conversion of elemental mercury to more oxidized forms has also shown that the acceleration of reactions can occur when environmentally relevant concentrations of Hg(0) and oxidants are frozen together in aqueous solutions. These observations, coupled with previous investigations into the effect of freezing on environmental reactions, lead us to conclude that this type of chemistry could potentially play a significant role in the chemical processing of a wide variety of inorganic components in polar regions. More recently, researchers have recognized the implications of these complementary field and laboratory findings toward human health and climate change. In this Account, we focus on the chemical and physical mechanisms that may promote novel chemistry and rate accelerations when water-ice is present. Future prospects will likely concentrate, once again, on the low-temperature chemistry of organic compounds, such as the humic acids, which are known cryospheric contaminants. Furthermore, data on the kinetics and thermodynamics of all types of reaction promoted by the freezing process would provide much assistance in determining their implications to environmental computer models.

Cold-surface photochemistry of selected organic nitrates.

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.

Freeze-induced formation of bromine/chlorine interhalogen species from aqueous halide ion solutions.

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 Cl(2)Br¯ 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 Br(2), to the gas-phase. This is a potentially important finding because Br(2) 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.

Dark oxidation of dissolved gaseous mercury in polar ice mimics.

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 (Hg(0)) 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 Hg(2+) ions when frozen in the presence of a variety of materials including hydrogen peroxide, nitrous acid and the sulfuric acid/O(2) couple.

Cold-surface photochemistry of primary and tertiary alkyl nitrites.

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 N(2)O 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.

Characterization of sulfurous acid, sulfite, and bisulfite aerosol systems.

Acidic tropospheric aerosols contain inorganic species such as sulfurous acid (H(2)SO(3)). As the main alkaline species, ammonia (NH(3)) 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 [NH(4)(+)]. The interactions between ammonia and hydrated sulfur dioxide (SO(2)·H(2)O) were studied at different humidities and concentrations. SO(2)·H(2)O is an important species as it represents the first intermediate in the overall atmospheric oxidation process of sulfur dioxide to sulfuric acid (H(2)SO(4)). This complex was produced within gaseous, aqueous, and aerosol SO(2) systems. The addition of ammonia gave mainly hydrogen sulfite (SHO(3)(-)) tautomers and disulfite ions (S(2)O(5)(2-)). These species were prevalent at high humidities enhancing the aqueous nature of sulfur(IV) species. Their weak acidity is evident due to the low [NH(4)(+)] produced. Size distributions obtained correlated well with the various stages of particulate compositional development.

Protonated nitrosamide and its potential role in the release of HONO from snow and ice in the dark.

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 DeNO(x) 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.

Freeze-induced reactions: formation of iodine-bromine interhalogen species from aqueous halide ion solutions.

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, IBr(2)(-). 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 IBr(2)(-) 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 IBr(2)(-) was thereby observed to occur up to pH <5.1, where the acidity levels are comparable to those found in the polar snowpack.

Airborne emissions in the harbour and port of Cork.

It is now accepted that the transport sector is responsible for a large and growing share of global emissions affecting both health and climate. The quantification of these effects requires, as an essential first step, a comprehensive analysis and characterization of the contributing subsectors, i.e. road transport, shipping, aviation and rail. The shipping contribution in dock/harbour areas is of particular interest because many vessels use old engines powered with old technology giving rise to high levels of particulate emissions mainly because the fuel employed contains high levels of sulphur, up to 4.5%. Large amounts of polyaromatic hydrocarbons and varying contents of transition metals are also detected. Few studies on the physicochemical composition of direct emissions from ship fuels have been performed; none have been compared to actual contents in local harbour or port atmospheres. The transformation of these ship-related materials to toxicologically active species may be much more efficient than corresponding road emission or domestic sources because of the expected highly acidic nature of the particulates. Surface, toxic material may therefore become readily bioavailable under such conditions but such studies have not been performed hitherto. This mini-review outlines in detail the issues raised above in the context of measurements made in Cork, Ireland.

On-line monitoring of airborne bioaerosols released from a composting/green waste site.

This study is the first to employ the on-line WIBS-4 (Wideband Integrated Bioaerosol Sensor) technique for the monitoring of bioaerosol emissions and non-fluorescing "dust" released from a composting/green waste site. The purpose of the research was to provide a "proof of principle" for using WIBS to monitor such a location continually over days and nights in order to construct comparative "bioaerosol site profiles". The real-time data obtained was then used to assess variations of the bioaerosol counts as a function of size, "shape", site location, working activity levels, time of day, relative humidity, wind speeds and wind directions. Three short campaigns were undertaken, one classified as a "light" workload period, another as a "heavy" workload period and finally a weekend when the site was closed. One main bioaerosol size regime was found to predominate: 0.5-3µm with morphologies ranging from elongated to ellipsoidal/spherical. The real-time number-concentration data provides a long-term "video" record of the site and were consistent with the Andersen sampling protocol performed that provides only a single "snapshot" for bioaerosol release. The number-concentration of fluorescent particles as a proportion of total particle counts amounted, on average, to ∼1% for the "light" workday period, ∼7% for the "heavy" workday period and ∼18% for the weekend. The bioaerosol release profiles at the weekend were considerably different from those monitored during the working weekdays.

Apportionment of urban aerosol sources in Cork (Ireland) by synergistic measurement techniques.

The sources of ambient fine particulate matter (PM2.5) during wintertime at a background urban location in Cork city (Ireland) have been determined. Aerosol chemical analyses were performed by multiple techniques including on-line high resolution aerosol time-of-flight mass spectrometry (Aerodyne HR-ToF-AMS), on-line single particle aerosol time-of-flight mass spectrometry (TSI ATOFMS), on-line elemental carbon-organic carbon analysis (Sunset_EC-OC), and off-line gas chromatography/mass spectrometry and ion chromatography analysis of filter samples collected at 6-h resolution. Positive matrix factorization (PMF) has been carried out to better elucidate aerosol sources not clearly identified when analyzing results from individual aerosol techniques on their own. Two datasets have been considered: on-line measurements averaged over 2-h periods, and both on-line and off-line measurements averaged over 6-h periods. Five aerosol sources were identified by PMF in both datasets, with excellent agreement between the two solutions: (1) regional domestic solid fuel burning--"DSF_Regional," 24-27%; (2) local urban domestic solid fuel burning--"DSF_Urban," 22-23%; (3) road vehicle emissions--"Traffic," 15-20%; (4) secondary aerosols from regional anthropogenic sources--"SA_Regional" 9-13%; and (5) secondary aged/processed aerosols related to urban anthropogenic sources--"SA_Urban," 21-26%. The results indicate that, despite regulations for restricting the use of smoky fuels, solid fuel burning is the major source (46-50%) of PM2.5 in wintertime in Cork, and also likely other areas of Ireland. Whilst wood combustion is strongly associated with OC and EC, it was found that peat and coal combustion is linked mainly with OC and the aerosol from these latter sources appears to be more volatile than that produced by wood combustion. Ship emissions from the nearby port were found to be mixed with the SA_Regional factor. The PMF analysis allowed us to link the AMS cooking organic aerosol factor (AMS_PMF_COA) to oxidized organic aerosol, chloride and locally produced nitrate, indicating that AMS_PMF_COA cannot be attributed to primary cooking emissions only. Overall, there are clear benefits from factor analysis applied to results obtained from multiple techniques, which allows better association of aerosols with sources and atmospheric processes.

The use of polar organic compounds to estimate the contribution of domestic solid fuel combustion and biogenic sources to ambient levels of organic carbon and PM2.5 in Cork Harbour, Ireland.

PM(2.5) samples collected at Cork Harbour, Ireland during summer, autumn, late autumn and winter, 2008-2009 were analyzed for polar organic compounds that are useful markers for aerosol source characterization. The determined compounds include tracers for biomass burning primary particles, fungal spores, markers for secondary organic aerosol (SOA) from isoprene, α-/ß-pinene, and d-limonene. Seasonal and temporal variations and other characteristic features of the detected tracers are discussed in terms of aerosol sources and processes. The biogenic species were detected only during the summer period where the contributions of isoprene SOA and fungal spores to the PM(2.5) organic carbon (OC) were estimated to be 1.6% and 1% respectively. The biomass burning markers, and in particular levoglucosan, were present in all samples and attributed to the combustion of cellulose-containing fuels including wood, peat, bituminous and smokeless coal. The contribution of domestic solid fuel (DSF) burning to the measured OC mass concentration was estimated at 10.8, 50, 66.4 and 74.9% for summer, autumn, late autumn and winter periods, respectively, based on factors derived from a series of burning experiments on locally available fuels. Application of an alternative approach, namely principal component analysis-multiple linear regression (PCA-MLR), to the measured concentrations of the polar organic marker compounds used in conjunction with real-time air quality data provided similar trends and estimates for DSF combustion during all seasons except summer. This study clearly demonstrates that, despite the ban on the sale of bituminous coal in Cork and other large urban areas in Ireland, DSF combustion is still the major source of OC during autumn and winter periods and also makes a significant contribution to PM(2.5) levels. The developed marker approach for estimating the contribution of DSF combustion to ambient OC concentrations can, in principle, also be applied to other locations.

Large pore bi-functionalised mesoporous silica for metal ion pollution treatment.

Here we demonstrate aminopropyl and mercatopropyl functionalised and bi-functionalised large pore mesoporous silica spheres to extract various metal ions from aqueous solutions towards providing active sorbents for mitigation of metal ion pollution. Elemental analysis (EA) and FTIR techniques were used to quantify the attachment of the aminopropyl and mercatopropyl functional groups to the mesoporous silica pore wall. Functionalisation was achieved by post-synthesis reflux procedures. For all functionalised silicas the functionalisation refluxing does not alter particle morphology/agglomeration of the particles. It was found that sorptive capacities of the mesoporous silica towards the functional groups were unaffected by co-functionalisation. Powder X-ray diffraction (PXRD) and nitrogen adsorption techniques were used to establish the pore diameters, packing of the pores and specific surface areas of the modified mesoporous silica spheres. Atomic absorption (AA) spectroscopy and inductively coupled plasma-atomic emission spectrometry (ICP-AES) techniques were used to measure the extraction efficiencies of each metal ion species from solution at varying pHs. Maximum sorptive capacities (as metal ions) were determined to be 384micromolg(-1) for Cr, 340micromol g(-1) for Ni, 358micromol g(-1) for Fe, 364micromol g(-1) for Mn and 188micromol g(-1) for Pd.

Potential role of the nitroacidium ion on HONO emissions from the snowpack.

The effects of photolysis on frozen, thin films of water-ice containing nitrogen dioxide (as its dimer dinitrogen tetroxide) have been investigated using a combination of Fourier transform reflection-absorption infrared (FT-RAIR) spectroscopy and mass spectrometry. The release of HONO is ascribed to a mechanism in which nitrosonium nitrate (NO+NO3-) is formed. Subsequent solvation of the cation leads to the nitroacidium ion, H2ONO+, i.e., protonated nitrous acid. The pathway proposed explains why the field measurement of HONO at different polar sites is often contradictory.

Spectroscopic and optimization modeling study of nitrous acid in aqueous solution.

Nitrous acid (HONO) and the nitrite ion represent a particularly important conjugate pair of trace species with regard to heterogeneous behavior within the bulk, and on the surface, of aqueous atmospheric dispersions: this role results from their chemical reactivity, photolysis pathways, solubility, and ambient concentration levels. The actual ratio of NO(2)(-): HONO in solution is determined by the pH and the nitrous acid dissociation constant (pK(a)) which is generally quoted in the literature as 3.27 at 298 K. However there is much disagreement in published works as to the exact value, which should be used in model calculations relevant to the atmosphere. Furthermore even though the nitrite ion is known to absorb solar radiation in the 300-400 nm region and represents a dominant source of *OH radicals in surface seawater, large variations in the measured molar decadic absorption coefficients, epsilon, for nitrite ions (and aqueous HONO) are evident in the literature. In the current study, using a UV-vis spectrometric approach with careful baseline subtraction, the relevant epsilon values for the nitrite ion were determined to be 8.16 +/- 0.08 M(-1) cm(-1) for the npi transitions at 290 nm and 22.1 +/- 0.22 M(-1) cm(-1) at 354 nm. For HONO, the wavelength maximum for the strongest vibronic band in solution was found at 372 nm with an epsilon value of 60.52 +/- 0.6 M(-1) cm(-1). Using the Henderson-Hasselbalch equation and the above data, a value of 2.8 +/- 0.1 is therefore reported here for the pK(a) of nitrous acid. A Newton-Gauss method was then employed to solve a set of nonlinear equations defining the chemical speciation model for HONO in solution using an algorithm written in FORTRAN 90. A model based on a simple one-step protonation worked well for intermediate pHs (6-3) but departed from the experimental observations in highly acidic media. A two-step equilibrium model involving the nitroacidium ion, H(2)ONO(+), gave a much closer fit in the very acidic region, while having little or no effect on the pH 6-3 section of the profile.

Cadmium-specific formation of metal sulfide 'Q-particles' by Klebsiella pneumoniae.

Klebsiella pneumoniae overcomes cadmium toxicity through the 'biotrans-formation' of cadmium ions into photoactive, nanometre-sized CdS particles deposited on the cell surface. The kinetics of particle formation during batch culture growth was monitored by electron microscopy (EM), energy-dispersive X-ray analysis and electronic absorption spectroscopy (EAS). During the deceleration phase of bacterial growth, the presence of CdS particles on the outer cell wall of K. pneumoniae (> or = 5 nm in diameter) was detected by EM. The size of these electron-dense particles continued to increase throughout the stationary phase of growth, with some of the particles reaching a diameter > 200 nm. The formation of the extracellular CdS particles contributed to around 3-4% of the total cell biomass. EAS undertaken on these extracellular 'bio-CdS' particles suggested that the large 'superparticles' observed by EM, e.g. 200 nm, were aggregates of smaller particles termed 'Q-particles', approximately 4 nm in diameter. Metal sulfide particles were not formed in batch cultures of K. pneumoniae grown in the presence of lead, zinc, mercury, copper or silver ions. Growth in the presence of lead ions resulted in the formation of extracellular electron-dense particles containing lead but not sulfide or phosphate. Intracellular phosphorus-containing electron-opaque particles were formed during growth in the presence of copper and mercury. Intracellular electron-dense particles were formed in the presence of zinc ions but these did not contain phosphorus. From these results it was thought that metal sulfide formation in K. pneumoniae showed some cadmium-specificity. When cadmium and zinc ions were both added to the growth medium, metal sulfide particles were formed that were predominantly composed of cadmium, e.g. 48.6% cadmium and 0.04% zinc. Similarly, when cadmium and lead ions were both present during growth only CdS particles formed. In both cases analysis of the cells by EAS confirmed the presence of CdS only. These observations suggest that the mechanism of CdS formation is unlikely to occur simply through a cadmium-induced release of hydrogen sulfide by the cells into the external environment. If hydrogen sulfide production was the mechanism of sulfide formation then metal sulfide particles containing lead and zinc ions in addition to cadmium ions should have been produced.