Robert W. Gillett

Formaldehyde production in clean marine air

The atmospheric mixing ratio of formaldehyde (HCHO) was measured continuously in clean marine air at the Australian Baseline Station at Cape Grim between mid November and mid December 1993. A diurnal cycle in mixing ratio was observed, consistent in amplitude with the expected photochemical source of this species. However the absolute values of the HCHO mixing ratio were higher than expected if the major source of HCHO under clean, low-NOx conditions is photolysis of methyl hydroperoxide (CH3OOH) derived from oxidation of methane by OH radicals. Possible explanations for elevated HCHO levels are considered. One sufficient to explain the observed HCHO levels is that reaction between hydroperoxy (HO2) and methylhydroperoxy (CH3O2) radicals may not proceed with 100% efficiency to form CH3OOH, but may have an additional branch yielding HCHO in clean marine conditions. There is some evidence from laboratory studies consistent with this proposal.

Fundamental ozone photochemistry in the remote marine boundary layer: the soapex experiment, measurement and theory

Abstract During the Austral summer of 1995, a series of measurements were made as part of the SOAPEX (Southern Ocean Atmospheric Photochemistry EXperiment) campaign at the Cape Grim Baseline Air Pollution station (41°S) on the north western tip of Tasmania, Australia. These measurements included peroxy radicals, photolysis parameters, speciated peroxides, NO x and other related chemical quantities. The climatology of Cape Grim is such that it frequently receives “ clean ” remote marine boundary layer air off the Southern Ocean and in this air in summer, there is clear evidence for the net photochemical destruction of ozone. The factors influencing the photochemical control of ozone are investigated by means of the relationship between peroxy radicals and j O( 1 D ) . From the levels of peroxy radicals and j O( 1 D ) , mid-day hydroxyl radical concentrations of (6±0.9)×10 6 moleculesxa0cm -3 are calculated, in agreement with other estimates in this region. An apparent discrepancy between measured and calculated peroxy radical levels in the “clean” atmosphere is investigated both from theoretical treatments and from the speciated peroxide record. The possible role of aerosols in the suppression of peroxy radicals are also discussed. Using simple photochemical theory the relative roles of photolysis and reaction with radicals are investigated in the observed −2.5xa0ppbv per day photochemical destruction of ozone. Measured values of j O( 1 D ) , calculated [OH] and the corrected peroxy radical concentration are used successfully to produce a simple fit to the ozone diurnal, illustrating the magnitude of the various contributing components, i.e. photolysis and reaction.

The Annual Cycle of Peroxides and Ozone in Marine Air at Cape Grim, Tasmania

The concentration of gas-phase peroxides has been measured almost continuously at the Cape Grim baseline station (41° S) over a period of 393 days (7702 h of on-line measurements) between February 1991 and March 1992. In unpolluted marine air a distinct seasonal cycle in concentration was evident, from a monthly mean value of>1.4 ppbv in summer (December) to <0.2 ppbv in winter (July). In the summer months a distinct diurnal cycle in peroxides was also observed in clean marine air, with a daytime build-up in concentration and decay overnight. Both the seasonal and diurnal cycles of peroxides concentration were anticorrelated with ozone concentration, and were largely explicable using a simple photochemical box model of the marine boundary layer in which the central processes were daytime photolytic destruction of ozone, transfer of reactive oxygen into the peroxides under the low-NOx ambient conditions that favour self-reaction between peroxy radicals, and continuous heterogeneous removal of peroxides at the ocean surface. Additional factors affecting peroxides concentrations at intermediate timescales (days to a week) were a dependence on air mass origin, with air masses arriving at Cape Grim from higher latitudes having lower peroxides concentrations, a dependence on local wind speed, with higher peroxides concentrations at lower wind speeds, and a systematic decrease in peroxides concentration during periods of rainfall. Possible physical mechanisms for these synoptic scale dependencies are discussed.

Relationships between ozone photolysis rates and peroxy radical concentrations in clean marine air over the Southern Ocean

Measurements of the sum of inorganic and organic peroxy radicals (RO2) and photolysis rate coefficients J(NO2) and J(O1D) have been made at Cape Grim, Tasmania in the course of a comprehensive experiment which studied photochemistry in the unpolluted marine boundary layer. The SOAPEX (Southern Ocean Atmospheric Photochemistry Experiment) campaign included measurements of ozone, peroxides, nitrogen oxides, water vapor, and many other parameters. This first full length paper concerned with the experiment focuses on the types of relationships observed between peroxy radicals and J(NO2), J(O1D) and √[J(O1D)] in different air masses in which ozone is either produced or destroyed by photochemistry. It was found that in baseline air with ozone loss, RO2 was proportional to √[J(O1D)], whereas in more polluted air RO2 was proportional to J(O1D). Simple algorithms were derived to explain these relationships and also to calculate the concentrations of OH radicals in baseline air from the instantaneous RO2 concentrations. The signal to noise ratio of the peroxy radical measurements was up to 10 for 1-min values and much higher than in other previous deployments of the instrument in the northern hemisphere, leading to the confident determination of the relationships between RO2 and J(O1D) in different conditions. The absolute concentration Of RO2 determined in these experiments is in some doubt, but this does not affect our conclusions concerned either with the behavior of peroxy radicals with changing light levels or with the concentrations of OH calculated from RO2. The results provide confidence that the level of understanding of the photochemistry of ozone leading to the production of peroxide via recombination of peroxy radicals in clean air environments is well advanced.

Size Distribution and Sources of Aerosol in Launceston, Australia, during Winter 1997

ABSTRACT As part of a pilot study into the chemical and physical properties of Australian fine particles, a suite of aerosol samples was collected at Ti Tree Bend in Launceston, Tasmania, during June and July 1997. This period represents midwinter in the Southern Hemisphere, a period when aerosol sources in Launceston are dominated by smoke from domestic wood burning. This paper describes the results from this measurement campaign, with the aim of assessing the effect of wood smoke on the chemical and physical characteristics of ambient aerosol. A micro orifice uniform deposit impactor (MOUDI) was used to measure the size distributions of the aerosol from 0.05 to 20 n m aerodynamic diameter. Continuous measurements of fine particle mass were made using a PM2.5 tapered element oscillating microbalance (TEOM) and light scattering coefficients at 530 nm were measured with nephelometers. Mass size distributions tended to be bimodal, with the diameter of the dominant mode tending to smaller sizes with increases in total mass. Non-sea salt potassium and polycyclic aromatic hydrocarbons (PAHs) were used as chemical tracers for wood smoke. Wood smoke was found to increase absolute particle mass (enough to regularly exceed air quality standards), and to concentrate mass in a single mode below 1 μm aerodynamic diameter. The acid-base equilibrium of the aerosol was altered by the wood smoke source, with free acidity hydrogen ion, non-sea salt sulfate, and ammonium concentrations being higher and the concentration of all species, including nitrate (to differing extents), focused in the fine particle size ranges. The wood smoke source also heavily influenced the aerosol scattering efficiency, adding to a strong diurnal cycle in both mass concentration and light scattering.

PIXE, PIGE AND ION CHROMATOGRAPHY OF AEROSOL PARTICLES FROM NORTHEAST AMAZON BASIN

Abstract Characterization of atmospheric aerosols collected in the northeast part of the Amazon Basin is presented. The main aerosol source in that region is the forest natural biogenic emission. The aerosol samples were collected using stacked filter units, and were analyzed applying several analytical techniques: Particle Induced X-ray Emission (PIXE) for the quantitative analysis of trace elements with Z > 11; Particle Induced Gamma-ray Emission (PIGE) for the quantitative analysis of Na; Ion Chromatography (IC) was used to quantify ionic contents of aerosols from the fine mode particulate samples. A reflectance technique was used in order to measure black carbon concentrations; Gravimetric analysis was used in order to determine the total atmospheric aerosol mass concentration. The comparison from PIXE and IC concentration measurements for S, K and Ca techniques were in an excellent agreement. A good agreement was also obtained for Na concentrations measured by PIGE and IC techniques. Multivariate statistical analysis was used in order to identify and characterize the sources of the atmospheric aerosol present in the sampled region. The Serra do Navio aerosol is characterized by biogenic emissions, responsible for the majority of the total fine mass concentration. A strong marine influence was also noted. Soil dust is also an important aerosol source in that region.

Short-term variability in marine atmospheric dimethylsulfide concentration

Dimethylsulfide (DMS) concentrations measured twice per hour in marine boundary layer air at the Cape Grim baseline station exhibit high variability over timescales as short as several hours. Major sources of this variability are identified as a diurnal cycle associated with the daytime destruction of DMS by reaction with hydroxyl radical, and a strong dependence upon wind speed, with high DMS concentrations at high wind speeds. The wind speed dependence was found to be broadly consistent with the wind speed dependence proposed by Liss and Merlivat [1986] for 10 m wind speed in the range 3.6 to 13 m s−1.

A universal bias in inorganic rainwater chemical composition data

[1]xa0In the late 1970s, it was recognised that organic acids contributed to the acidity and ionic content of rainwater, but that these acids had not been detected because they were consumed biologically in the period between rainwater collection and subsequent laboratory analysis. Discussion of consequences for measured rainwater composition has been limited to assessment of pH gain that attends organic acid loss. We show that biological effects on rainwater ionic composition are not restricted to pH alone. Ammonium, potassium, nitrate, sulfate, methanesulfonate, and phosphate ions are also removed biologically, but remain in the rainwater in biomass, implying that most previous rainwater composition studies based on ionic analyses will have systematically underestimated nutrient deposition.

Atmospheric short-chain-chlorinated paraffins in Melbourne, Australia – first extensive Southern Hemisphere observations

Environmental context This study presents the first comprehensive set of ambient atmospheric concentrations of short-chain-chlorinated paraffins in the Southern Hemisphere. The data show a seasonal cycle with a summer maximum and a winter minimum. The seasonal cycle is consistent with temperature dependence of the vapour pressure of the short-chain-chlorinated paraffins resulting in partitioning between the atmosphere and other reservoirs with a secondary modulation by soil moisture. Abstract The first extensive measurements of short-chain chlorinated paraffins (SCCPs) in the atmosphere of the Southern Hemisphere are presented. The analytical and sampling methodologies used in this Australian study were verified by systematic testing along with two inter-comparisons with Northern Hemisphere laboratories with established SCCP programs. In the ambient atmosphere of Melbourne, Australia, in 2013–14, there was a clear seasonal cycle in SCCP monthly averaged concentrations, these ranging from 28.4ng m–3 in summer to 1.8ng m–3 in winter. Air temperature was the factor most closely related to the seasonal cycle in SCCPs in Melbourne. The average SCCP concentrations observed indoors were less than those observed outdoors. Atmospheric concentrations of SCCPs in Melbourne are more than two orders of magnitude higher than concentrations in the background atmosphere. Surprisingly, the SCCP concentrations in Melbourne are similar to those observed in cities in Japan, South Korea and the United Kingdom, and less than those observed in China. Direct transport of SCCPs in the atmosphere from the Northern Hemisphere emissions to Melbourne is ruled out. Instead elevated concentrations in the Melbourne air-shed are most likely a result of the long-term import of SCCPs as industrial chemicals and within manufactured materials from the Northern Hemisphere so that the use of SCCPs in Melbourne and their consequent release to the environment has produced environmental reservoirs of SCCPs in Melbourne that are comparable with those in some Northern Hemisphere cities. The increase in SCCP concentrations from winter to summer is consistent with the temperature dependence of partitioning of SCCPs between the atmosphere and other reservoirs. Insufficient information exists on SCCP use and its presence in soils and sediments in Australia to indicate whether the atmospheric presence of SCCPs in Melbourne is a legacy issue due to its import and use as a metal cutting agent in past decades or due to ongoing imports of manufactured materials containing SCCPs today.