R. W. Gillett

Chloride and Bromide Loss from Sea-Salt Particles in Southern Ocean Air

Datasets on aerosol composition in Southern Ocean air at Cape Grim and Macquarie Island, and rainwater composition at Cape Grim, have been analysed for sea-salt components in order to test the validity of the multiphase autocatalytic halogen activation process proposed initially by Sander and Crutzen (1996) and developed fully for clean marine air by Vogt et al. (1996). Four distinct datasets from the two locations were analysed. All four datasets provided consistent evidence in support of three predictions of the autocatalytic model: (1) overall Cl- deficits in sea-salt aerosol were small, difficult to quantify against analytical uncertainty and at most a few percent; (2) Br- deficits were large, averaging −30% to −50% on an annual basis, with strong seasonality ranging from about −10% in some winter samples to −80% or more in some summer samples; and (3) the Br- and Cl- deficits were clearly linked to the availability of strong, S-acidity in the aerosol, confirming the importance of acid catalysis to the dehalogenation process.

Relationships between size segregated mass concentration data and ultrafine particle number concentrations in urban areas

Abstract Mass concentration data derived from samples collected with a micro-orifice uniform deposit impactor (MOUDI) in six Australian urban centers during periods of significant particle loading have been used to investigate the relationships between TSP, PM10, PM2.5, PM1 and ultrafine particles. While PM10 and PM2.5 display a clear relationship, the lack of correlation between PM10 and the coarse fraction of PM10 (PM10–PM2.5) suggests that variation in PM10 is dominated by variance in PM2.5. Given that particles of less than 2.5 μm are suspected to have adverse health effects, increasing the extent of PM2.5 monitoring may improve detection of relationships between air pollution and human health. A lack of correlation between both PM10 and PM2.5 with ultrafine mass concentrations indicates that PM10 and PM2.5 cannot be used as a surrogate for ultrafine mass concentration. Similarly, ultrafine number concentrations cannot be inferred from mass concentration information determined by the MOUDI.

Isoprene emissions from vegetation and hydrocarbon emissions from bushfires in tropical Australia

Information from a variety of sources, including an airborne field expedition in November 1985, is used to produce estimates of the annual emissions of some hydrocarbons from bushfires, and isoprene from trees, in tropical Australia. For the continent north of 23° S the annual bushfires (biomass burning) input was estimated, in units of Tg carbon, to be 2 TgC (uncertainty range 0.8–5 TgC), emitted predominantly during the May to October dryseason. Isoprene emissions during this period were estimated also to be 2 TgC (uncertainty range 0.5–8 TgC), but were estimated to be an order of magnitude higher during the November to April wet season, at a level of 23 TgC (uncertainty range 6–100 TgC).The large annual emission of isoprene over the tropical part of the Australian continent yields ppbv levels of isoprene measured at the surface in summertime. Isoprene reactivity with hydroxyl radical is such that at these concentrations isoprene must be a dominant factor in controlling the concentration of OH radical in the convective boundary layer. Simple arguments based on the convective velocity scale suggest that the shape of the isoprene vertical profile in November 1985 would be consistent with available data on the OH-isoprene reaction rate if OH concentration in the boundary layer averaged about 2.5×106 cm-3 over the middle part of the day.

Rainwater Composition and Acidity at Five Sites in Malaysia, in 1996

Rainwater chemical composition and acidity were determinedfrom weekly-averaged wet-only rainwater samples collected atfive sites in Malaysia throughout 1996. The major aim of thiswork was to assess the extent to which acid deposition, foundpreviously at one site in the Klang Valley, was a general,rather than local, phenomenon. To this end, three measurementsites were located spanning the length of the Klang Valley (anurban-industrial region of approximately 3000 km2containing the Malaysian capital, Kuala Lumpur). A fourth sitewas located outside, but adjacent to the Klang Valley, and thefinal site was located 300 km to the southeast, in anurban/industrial region adjacent to Singapore. Annual pHvalues in the range 4.16–4.40 and estimated total depositionfluxes of acidic sulfur and nitrogen species in the range 120–350 meq m-2 yr-1 show all sites to be impactedsignificantly by acidic deposition. Average contributionswere 60% as sulfur species, 40% as nitrogen species. Theresults confirm that potentially significant levels of aciddeposition occur in Malaysia as a regional phenomenonassociated with urban/industrial activities.

Thymol as a Biocide in Japanese Rainwater

Rainwater samples (wet-only; event samples) collected in Niigata in late autumn 1996 and springtime 1997 were used to assess the effectiveness of thymol as a biocide in Japanese rainwater. Upon collection each rainwater sample was divided into sub-samples, with thymol added to one sub-sample. Sub-samples with and without thymol were shipped to CSIRO, Australia, for chemical analysis. Comparison of analytical results for each pair of sub-samples proved the effectiveness of thymol in preventing biological action in this region where effects of rainwater microflaura and fauna on rainwater composition have not before been studied. Sub-samples without thymol exhibited lowered electrical conductivity, loss of the cations H+ and NH4-, and loss of the anions HCOO-, CH3COO-, C2O42-, CH3SO3- and PO43-. Nitrate showed no change in all but one of the samples, indicating that ammonia was the preferred source of nitrogen for the biological processes that consumed the rainwater organic acids and phosphate. These results suggest that thymol is a suitable rainwater biocide for use under Japanese conditions.

Volatile organic compounds in marine air at Cape Grim, Australia

Environmental context. Gaseous organic compounds fuel the production of ozone in the background lower atmosphere. There have been no measurements of many of these compounds in the temperate and polar latitudes of the Southern Hemisphere. Here some first results are presented that show in general much lower concentrations than the Northern Hemisphere, due in part to the lower land surfaces and biomass burning in the Southern Hemisphere. Abstract. Measurements were made of volatile organic compounds (VOCs) at Cape Grim using proton transfer reaction mass spectrometry (PTR-MS) during the Precursors to Particles (P2P) Campaign from 10 February to 1 March 2006. Approximately 14 days of clean air data were obtained along with 4 days of data from when polluted air, first from a smoke plume from a fire on Robbins Island adjacent to the station and then air from Victoria, was present. This paper deals with the results obtained in clean air, the focus of the P2P campaign. The protonated masses and probable VOCs measured in the clean marine air were: methanol, 33; acetonitrile, 42; acetaldehyde, 45; acetone, 59; isoprene, 69; methylvinyl ketone/methacrolein (MVK/MACR), 71; methylethyl ketone, 73; and benzene, 79. The measurements at Cape Grim were in some cases near the detection limit and an analytical challenge. The range of concentrations detected in clean maritime air, the relationship to the limited range of previous measurements in marine air in the Northern Hemisphere tropics, and the physical, chemical and biological processes controlling these compounds in the marine air are discussed. The methanol concentrations observed at Cape Grim are consistent with global modelling, incorporating sources that are mainly of vegetation origin. Isoprene has recently been implicated as a precursor to cloud condensation nuclei over the Southern Ocean. In this snapshot of observations at Cape Grim, Tasmania, isoprene and the isoprene oxidation products MVK and MACR appeared to be absent in air from the Southern Ocean. However, isoprene has a very short atmospheric lifetime and the spatial distribution of its emissions may be very heterogeneous. The concentrations of the other VOCs in marine air at Cape Grim, acetonitrile, acetaldehyde, acetone, methylethyl ketone and benzene, were typically a factor of four lower than that observed over the remote tropical ocean in the Northern Hemisphere. The lower concentrations of carbonyls and their precursor hydrocarbons may indicate a limitation on ozone production potential in the Southern Hemisphere compared with the Northern Hemisphere troposphere. Additional keywords: atmospheric composition, oxygenated volatile organic compounds, proton transfer reaction mass spectrometry, Southern Ocean, volatile organic compounds.

Concentrations of nitrogen and sulfur species in gas and rainwater from six sites in Indonesia.

Gas mixing ratios of SO2, NO2 and HNO3 and nitrate and sulfate concentrations in rainwater have beenmeasured at six sites in Indonesia. The sites, Jakarta, Serang,Cilegon, Merak and Bogor, in Java, and Bukit Koto Tabang inSumatra, provide a range of pollution regimes in Indonesia.Jakarta and Bogor are heavily polluted sites in Java, whereasBukit Koto Tabang is a clean air station in a relativelyunpopulated area on the west coast of equatorial Sumatra. At thesesites rainwater was collected daily and gas samples weeklyduring 1996. The other three sites Serang, Cilegon and Merakrepresent smaller regional towns in west Java. At these sitesrainwater samples were collected weekly from June 1991 untilJune 1992.The results show that Jakarta has the highest volume-weightedmean sulfate concentrations in rainwater while the lowest weremeasured at Bukit Koto Tabang. Volume-weighted mean nitrateconcentration was about 24 μeq L-1 at Jakarta and Bogor,significantly higher than the 0.8 μeq L-1 measured atBukit Koto Tabang.Sulfur dioxide mixing ratios ranged from 4–7 ppbv in Jakarta toan average of 1.3 ppbv at Bukit Koto Tabang. Nitrogen dioxidemixing ratio was highest in Jakarta averaging 28 ppbv comparedwith the background mixing ratio of 1.2 ppbv at Bukit KotoTabang. Using dry deposition velocities estimated during aseparate study in the similar conditions of Malaysia enabled drydeposition estimates of SO2, HNO3 and NO2.Results of estimated total acidic S and N deposition (wet anddry) were greater than 250 meq m-2 yr-1 at the Jakartaand Bogor sites compared with about 23 meq m-2 yr-1 atBukit Koto Tabang. At Jakarta and Bogor dry deposition accountedfor more than 50% of the total deposition estimates compared with about 20% at Bukit Koto Tabang. Such deposition rates arehigh when compared to critical loads estimated for Indonesia bythe RAINS-Asia model. In this model, critical loads in western Java and equatorial western Sumatra fall into one of twoclasses: 50–100 and 20–50 meq m-2 yr-1. Thus acidic deposition flux at Jakarta and Bogor wasfound to be above the predicted critical loads even for the moreacid insensitive soils.

Atmospheric concentrations and deposition of oxidised sulfur and nitrogen species at Petaling Jaya, Malaysia, 1993–1998

Wet-only rainwater composition, acid-precursor gas mixing ratios and aerosol loading were determined from weekly-averaged samples at Petaling Jaya, Malaysia, over the five year period from March 1993 to March 1998. Annual deposition fluxes of acidic sulfur and nitrogen species estimated from these data show this site to be heavily impacted by acidic deposition, with total oxidised sulfur plus nitrogen deposition in the range 277–480 meq m-2 yr-1. Average contributions were 56% as sulfur species, 44% as nitrogen species, with wet deposition in this region of high rainfall accounting for 67% of total deposition. Thus total acid deposition fluxes were equivalent to levels that provided motivation for emissions reduction programs in both Europe and North America. The possibility of adverse environmental effects in Malaysia caused by acid deposition therefore merits serious consideration and assessment.

Some observations on the acidity and composition of rainwater in Sydney, Australia, during the summer of 1980–81

During the summer of 1980–81, a rudimentary form of wet-only event sampling was employed to collect a total of 294 rainwater samples at 12 sites spread across the metropolitan region of Sydney, Australias largest city. From the samples were determined conductivity, pH, ammonium, chloride and nitrate ion concentrations as well as deposited water volume. Supplementary data consisting of city-wide averaged SO2, NO2, NO, and O3 concentrations and 950 mb wind speed and direction were obtained for times coinciding with the period during which each event occurred.The pH of rainwater upwind of the city and unaffected by urban/industrial emissions was found to be usually ≥5, whereas the volume-weighted mean pH of all the metropolitan samples was 4.4, indicating that local emissions significantly increased rainwater acidity in the near field. Time available for conversion of precursors to acids averaged 1–2 h only.Considerable day-to-day variability in rainwater composition was observed. Factors identified as contributing to this variability included precursor gas concentration, wind speed, wind direction, amount of water deposited per event and possibly time of day. These results show that physical/meteorological factors cannot be excluded from consideration if variance in rainwater composition data is to be explained.

Quantification of secondary organic aerosol in an Australian urban location

Environmental context Particulate matter is detrimental to human health necessitating air quality standards to ensure that populations are not exposed to harmful levels of air pollutants. We quantified, for the first time in an Australian city, secondary organic aerosol produced in the atmosphere by chemical reactions, and show that it constitutes a significant fraction of the fine particulate matter. Secondary organic aerosol should be considered in regulations to control particulate matter and ozone. Abstract The contribution of secondary organic aerosol (SOA) to particulate mass (PM) in an Australian urban airshed is quantified for the first time in this work. SOA is estimated indirectly using the elemental carbon tracer method. The contribution of primary organic carbon (OC) to PM is determined using ambient air quality data, which is used to indicate photochemical activity and as a tracer for a general vehicular combustion source. In addition, levoglucosan concentrations were used to determine the contribution of wood heater emissions to primary OC. The contribution of bushfire smoke to primary OC emissions was determined from the organic and elemental carbon (OC/EC) ratios measured in bushfire source samples. The median annual SOA concentration determined in this work was 1.1 µg m–3, representing ~13% of PM2.5 median concentrations on an annual basis (assuming a ratio of organic mass (OM) to OC of 1.6). Significantly higher SOA concentrations were determined when bushfire smoke affected the airshed; however, the SOA fraction of PM2.5 was greatest during the autumn and early winter months when the formation of inversions allows build up of particles produced by domestic wood-heater emissions.