David Shooter

Photo-oxidation of dimethylsulphide in aqueous solution

Abstract Dimethylsulphide (DMS) is readily photo-oxygenated in the presence of micromolar amounts of photosensitizers such as methylene blue, rose bengal, anthroquinone and humic acid. Two moles of DMS are oxidized for every mole of molecular oxygen utilized consistent with dimethyl-sulphoxide being the oxidation product. Coastal seawater samples examined contained sufficient naturally occurring photosensitizer to photo-oxygenate DMS in sunlight with a first order rate constant of 2.4 × 10 −5 s −1 . This rate is rapid enough to imply that DMS is oxidized at approximately the same rate as it is lost to the atmosphere.

Environmental monitoring in four European museums

In a European multidisciplinary research project concerning environmental diagnostics, museums have been selected, having different climate and pollution conditions, i.e.: Correr Museum, Venice (Italy); Kunsthistorisches Museum, Vienna (Austria); Royal Museum of Fine Arts, Antwerp (Belgium); Sainsbury Centre for Visual Arts, Norwich (UK). Some field tests investigated the microclimate, the gaseous and particulate air pollution and the biological contamination to suggest mitigative techniques that may reduce the potential for damage in the long run. Potential risk factors are generated by imbalance in temperature and humidity, generated by heating, air conditioning or ventilating system (HVAC), or the building structures, exchange of outside air, or large visitor numbers. HVAC may also enhance indoor gaseous pollution. Plants and carpets represent potential niches for bacterial colonisation. Pollutants and particles have been recognised having partly external and partly internal origin. Tourism has a direct negative impact, i.e. transport of external particles, release of heat, vapour and CO2, as well as generation of turbulence, which increases the deposition rate of particulate matter. However, the main problem is that the microclimate has been planned for the well being of visitors during only the visiting time, disregarding the needs of conservation that requires a constant climate by day and by night. In some of these cases, better environmental niches have been obtained with the help of showcases. In other cases, showcases worsened the situation, especially when incandescent lamps were put inside

Indoor air quality at the Correr Museum, Venice, Italy

Two multidisciplinary field surveys, one in winter and the other in summer have monitored the indoor microclimate, air pollution, deposition and origin of the suspended particulate matter and microorganisms of the Correr Museum, Venice. In addition, this study was focused to identify the problems caused by the heating and air conditioning system (HAC) and the effects due to the presence of carpets. Heating and air conditioning systems (HACs), when chiefly designed for human welfare, are not suitable for conservation and can cause dangerous temperature and humidity fluctuations. Improvements at the Correr Museum have been achieved with the assistance of environmental monitoring. The carpet has a negative influence as it retains particles and bacteria which are resuspended each time people walk on it. The indoor/outdoor pollutants ratio is greater in the summertime, when doors and windows are more frequently open to allow for better ventilation, illustrating that this ratio is mainly governed by the free exchange of the air masses. The chemical composition, size and origin of the suspended particulate matter have been identified, as well as the bacteria potentially dangerous to the paintings. Some general suggestions for improving indoor air quality are reported in the conclusions.

Water soluble ions of atmospheric aerosols in three New Zealand cities: seasonal changes and sources

The results of one years measurements (typically a two week sampling campaign in each season) of the concentrations of eight major water soluble ions, namely Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3− and SO42−, in atmospheric aerosols collected in three New Zealand cities (Auckland, Christchurch and Hamilton) are presented. The data has provided important information on particulate soluble ion profiles in New Zealand urban areas and revealed some useful trends. A significant correlation has been found between the average meteorological conditions in a sampling campaign and the average particulate concentrations of some of these soluble ions in the campaign. For example, average particulate NO3− concentration in a campaign was found to correlate well with the average calm or weak wind duration percentage in the campaign, and the average concentrations of Na+, Mg2+ and Cl− related closely to the average wind pattern and rainfall in the campaign. Significant site and seasonal variations have been observed with Hamilton having the lowest overall concentrations of all the soluble ions in the particles sampled. On average all sites had the highest particulate concentrations of Na+, Mg2+ and Cl− in the summer but the highest particulate concentrations of NH4+ and non-sea-salt Ca2+ (nss-Ca2+) in the winter. The possible sources of PM10 mass have been deduced and in particular the relative contribution of sea salts to PM10 mass in the cities are reported.

Observations of the preferential loss of major ions from melting snow and laboratory ice

Abstract Two types of laboratory experiments were undertaken to understand changes in the ionic composition of solutions from melting snows: (1) a set of field-laboratory experiments which involved partially melting recently collected snows and (2) experiments on the controlled melting of artificial ices of known composition. Sulphate and nitrate ions are preferentially lost with respect to chloride during the melting process so apparent elution sequence may be written SO 4 2− > NO 3 − > Cl − . Of the cations, sodium appears to be removed least readily giving an elution sequence Mg 2+ = K + > Na + . In the laboratory the differences in the efficiency of removal of ions from ice are small in the first stages of melting, but pronounced by the end of the melt. Sodium and chloride are expected to be proportionally enriched in residual leached snow packs. This is generally born out by field observations. The preferential loss of some ions is more evident in aged laboratory ice than in the freshly made ice. The changes in the ice and meltwater composition throughout the process of melting may be understood to arise from the mixing of two types of solutions: (i) an intergranular surficial brine with high solute concentration that occupies the ice grain boundaries and (ii) the meltwater from the ice grains.

Dimethylsulphide oxidation in the ocean

Abstract Dimethylsulphide (DMS) is generally thought to be lost from the ocean by transfer to the atmosphere. However DMS is slowly autoxidized in saline solution (k′ = 2.2 × 10−8s−1 at pH 8 and 20°C). The rate of autoxidation decreases with increasing pH and has an activation energy of 78 kJ mol−1 at pH 8. Although slow, this autoxidation is fast enough to require a deep-sea source (precipitating detrital material?) for the low concentrations of DMS found at great depths. DMS does not bind significantly to Cu, Cd, Zn and Pb in seawater, although Cu was observed to increase the rate of autoxidation.

Coarse–fine and day–night differences of water-soluble ions in atmospheric aerosols collected in Christchurch and Auckland, New Zealand

Abstract The water-soluble ions in fine (PM ) and coarse (PM 2.5−10 ) atmospheric aerosols collected in Christchurch during winter 2001, spring 2000 and summer 2001, and in Auckland during winter 2001 have been studied in terms of coarse–fine and day–night differences. Although the chemical characteristics of the coarse particles were similar in both cities, those of the fine particles collected in the Christchurch winter were significantly different, as manifested by higher concentrations of nss-K + , nss-Cl − , nss-Ca 2+ , nss-SO 4 2− , NO 3 − and NH 4 + . It was found that nighttime PM 10 and nss-K + concentrations were much higher than their daytime concentrations in the Christchurch winter but a clear day–night difference was not apparent in the Auckland winter. Moreover, in the winter, sea-salt ions did not show a day–night difference; however, nss-SO 4 2− had opposite day–night variation in the two cities. An ion balance calculation has shown that in most samples, coarse particles can be neutral or alkaline, however, fine particles can be neutral or acidic. The possibility of ammonium salts existing in the fine particles collected in the Christchurch winter is discussed and it is concluded that a variety of ammonium salts were present. Equivalent ratios suggest that the fine particles may be significantly aged in the Christchurch winter. The evidence from our soluble ion study strongly suggests that wood and coal burning and secondary aerosols make a significant contribution to fine particulate mass in the Christchurch atmosphere. Thus, home-heating, a sheltered geographic location and relatively calm atmospheric condition are thought to be the major causes for the serious atmospheric particulate pollution in the Christchurch winter.

Air quality indexing

In an attempt to meet the publics needs for information on air quality a variety of indexes have been developed and they continue to evolve. To show the complexity and the diversity of such indices, a variety of current air quality indices are described here and compared in regard to their performance and ability to deliver quality information. A number of characteristics seem desirable for an index: consistency, simplicity, versatility and flexibility. In terms of their ongoing development, an AQI also needs to be useful for forecasting, and the method of calculation needs to be sufficiently flexible to allow for pollutants to be added or subtracted as changes to their health impact are revealed. However, much progress is still to be made, mainly through more careful consideration of the combined impact of multiple pollutants, consideration of low level exposure, and with more timely transfer of usable information to the public.

Volatile reduced sulphur compounds in butter by solid phase microextraction

The reduced sulphur volatiles, methanethiol and dimethyldisulphide (but not dimethylsulphide), have been detected in the headspace of butter samples. Their concentrations in the butter itself were calculated by determination of the distribution coefficient ( K ) through spiking butter samples with known quantities of methanethiol and dimethyldisulphide. The K values obtained suggest that the dimethyldisulphide had a greater affinity than methanethiol for the lipid phase of the butter. Solid phase microextraction used in conjunction with gas chromatography–mass spectrometry has been shown to be an effective method for headspace analysis and was used for quantifying the butter headspace concentrations of the reduced sulphur compounds. Seasonal variation of both methanethiol and dimethyldisulphide were found in a series of butter samples, the highest concentration being in spring with an overall decrease through the New Zealand summer. Grass type and condition appeared to influence the concentrations of these compounds in the butter. Storage of the series of butter samples at 4°C for 5 weeks resulted in a significant decrease in the concentrations of both methanethiol and dimethyldisulphide. The dimethylsulphide concentration in all butter samples was below the detection limit of the analytical system used.

A passive sampler for hydrogen sulfide

The silver nitrate/fluorescein mercuric acetate fluorimetric method for the measurement of atmospheric hydrogen sulfide has been adapted to passive sampling. Standard samplers have been tested and used in both indoor and outdoor environments. Sampler performance was not dependent on construction materials or sunlight intensity and gave similar results to active sampling. Two case studies were carried out, one in the Horniman Museum and its associated storage and study building, London, UK, and the other in the vicinity of a pulp and paper mill and geothermal area North Island, New Zealand. The detection limit of the samplers (50 ppt average for a one-week exposure) provides the opportunity to make measurements in a variety of locations provided exposure times are sufficiently long, i.e., up to one month in areas of low hydrogen sulfide concentration.