Origins and sources of atmospheric precipitation from australia: chlorine-36 and major-element chemistry

Temporal and spatial variations of major-element and 36Cl chemistry in rainfall across Australia have been assessed. Bulk precipitation samples were collected from two arrays over two years at three-monthly intervals: the WE array (10 sites) extended in a west to east direction from the coast of Western Australia south of Geraldton, inland to Warburton in Central Australia, and the SN array (8 sites), extended in a south to north direction from Port Lincoln in South Australia to Kakadu in the Northern Territory. The major-element chemistry shows that the main influence en the composition of precipitation in remote areas of Australia is mixing between seawater and continental sources. At most sites along the two arrays it is difficult to distinguish between the separate end-members of this source, except at coastal localities where seawater dominates the chemistry of precipitation. However, the influence of seawater is also evident at non-coastal sites in association with favourable synoptic conditions, such as cold frontal activity in south and western Australia during winter, and monsoonal activity in northern Australia during summer. The continentally-derived end-member is most likely composed of resuspended soil/dust material, including salt-lake and calcareous dune components. In the south of the SN array where agriculture is intense this continental source variably includes a fertiliser component. The chemistry of precipitation across Australia is also affected by an acid-base balance factor, the components of which are derived from natural sources such as biogenic emissions, biomass burning and lightning flash production. The nature of the collection program (i.e. samples are exposed to the atmosphere from the time of deposition to the time of sample retrieval) means biodegradation is also evident in the collected sample chemistry. Chlorine-36 is a cosmogenic isotope with a half-life of 301,000 years. This time frame, combined with the hydrophilic nature of Cl, makes 36Cl useful as a hydrological tracer. The use of 36Cl as a hydrological tracer however, relies on predicted models of 36Cl and stable Cl fallout to calculate 36CJ/CJ ratios for recharge to hydrological systems. The results from this investigation agree with the general shape of the latitude-dependent theoretical 36Cl fallout curve of Lal and Peters (1967), but suggests that the curve underestimates the rate of fallout. A revised mean fallout for the southern hemisphere of 15.4 36CI atomsfm2/s is suggested, and long-term average predictions of 36CJ fallout rates used to predict the input ratios of iv 36CIJC1 in hydrological investigations should be increased by a factor of 1.4 for the southern hemisphere. Further, while stable Cl concentrations in precipitation display a general exponential decrease with distance from the coast, the nature of this relationship is geographically variable, and Cl concentrations in precipitation should be investigated for each study by local direct measurements, a process that is simple and inexpensive. The mean 36Cl fallout for the southern hemisphere, calculated from this work is three times lower than has been measured for precipitation in the northern hemisphere. The lower southern hemisphere fallout rates reflect the lower rates of transfer of stratospheric air to the troposphere in the southern hemisphere, which results from the less dynamic nature of the lower stratosphere in the southern hemisphere. The mean global 36Cl fallout that incorporates measurements from the northern hemisphere with the results of this work is calculated to be 25-35 atomsfm2fs, 2-3 times greater than predicted by Lal and Peters (1967). This suggests that the cross-section for the cosmic-ray production of 36Cl may be underestimated in their paper. This work supports the use of 36Cl as a tracer of atmospheric processes. Is production primarily in the stratosphere suggests that it may trace stratospheric-tropospheric exchange. Seasonal variations in 36Cl fallouts and 36ClJCl show high ratios and fallouts during spring, and at some localities, during summer (i.e. the north of the SN array). The increased spring 36Cl fallouts are attributed to increased transfer of stratospheric 36Cl to the troposphere that occurs as the tropopause height increases during the warmer months. High fallouts during summer in the north of the SN array may be attributed to the direct entrainment of stratospheric air into cumulus clouds during the monsoonal convection. Chlorine-36 exists in the stratosphere predominantly as HCl gas (Wahlen et al 1991). The correlation between 36CJ and N03 and the lack of any relationship between 36Cl, stable Cl and Na concentrations (the latter being entrained as aerosols), suggest that 36Cl is scavenged from the atmosphere as a gas rather than an aerosol phase

Atmospheric mercury in the Latrobe Valley, Australia : case study June 2013

Gaseous elemental mercury observations were conducted at Churchill, Victoria, in Australia from April to July, 2013, using a Tekran 2537 analyzer. A strong diurnal variation with daytime average values of 1.2–1.3 ng m–3 and nighttime average values of 1.6–1.8 ng m–3 was observed. These values are significantly higher than the Southern Hemisphere average of 0.85–1.05 ng m–3. Churchill is in the Latrobe Valley, approximately 150 km East of Melbourne, where approximately 80% of Victoria’s electricity is generated from low-rank brown coal from four major power stations: Loy Yang A, Loy Yang B, Hazelwood, and Yallourn. These aging generators do not have any sulfur, nitrogen oxide, or mercury air pollution controls. Mercury emitted in the 2015–2016 year in the Latrobe Valley is estimated to have had an externalized health cost of $AUD88 million. Air pollution mercury simulations were conducted using the Weather Research and Forecast model with Chemistry at 3 × 3 km resolution. Electrical power generation emissions were added using mercury emissions created from the National Energy Market’s 5-min energy distribution data. The strong diurnal cycle in the observed mercury was well simulated (R2 ¼ .49 and P value ¼ 0.00) when soil mercury emissions arising from several years of wet and dry deposition in a radius around the power generators was included in the model, as has been observed around aging lignite coal power generators elsewhere. These results indicate that long-term air and soil sampling in power generation regions, even after the closure of coal fired power stations, will have important implications to understanding the airborne mercury emissions sources. Copyright: © 2021 The Author(s). **Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Melita Keywood” is provided in this record*

Szenci Molnár Albert epigrammája a Scandell-antológiában

The composition of secondary organic aerosol (SOA) from the ozonolysis of C5−C8 cycloalkenes and α-pinene, as well as the effects of hydrocarbon precursor structure and particle-phase acidity on SOA formation, have been investigated by a series of controlled laboratory chamber experiments. A liquid chromatography−mass spectrometer and an ion trap mass spectrometer are used concurrently to identify and to quantify SOA components with molecular weights up to 1600 Da. Diacids, carbonyl-containing acids, diacid alkyl esters, and hydroxy diacids are the four major classes of low-molecular-weight (MW \u3c 250 Da) components in the SOA; together they comprise 42−83% of the total SOA mass, assuming an aerosol density of 1.4 g/cm3. In addition, oligomers (MW \u3e 250 Da) are found to be present in all SOA. Using surrogate standards, it is estimated that the mass fraction of oligomers in the total SOA is at least 10% for the cycloalkene systems (with six or more carbons) and well over 50% for the α-pinene system. Higher seed particle acidity is found to lead to more rapid oligomer formation and, ultimately, to higher SOA yields. Because oligomers are observed to form even in the absence of seed particles, organic acids produced from hydrocarbon oxidation itself may readily promote acid catalysis and oligomer formation. The distinct effects of carbon numbers, substituent groups, and isomeric structures of the precursor hydrocarbons on the composition and yield of SOA formed are also discussed

Measurements of Secondary Organic Aerosol from Oxidation of Cycloalkenes, Terpenes, and m-Xylene Using an Aerodyne Aerosol Mass Spectrometer

The Aerodyne aerosol mass spectrometer (AMS) was used to characterize physical and chemical properties of secondary organic aerosol (SOA) formed during ozonolysis of cycloalkenes and biogenic hydrocarbons and photooxidation of m-xylene. Comparison of mass and volume distributions from the AMS and differential mobility analyzers yielded estimates of “effective” density of the SOA in the range of 0.64−1.45 g/cm3, depending on the particular system. Increased contribution of the fragment at m/z 44, CO2+ ion fragment of oxygenated organics, and higher “Δ” values, based on ion series analysis of the mass spectra, in nucleation experiments of cycloalkenes suggest greater contribution of more oxygenated molecules to the SOA as compared to those formed under seeded experiments. Dominant negative “Δ” values of SOA formed during ozonolysis of biogenics indicates the presence of terpene derivative structures or cyclic or unsaturated oxygenated compounds in the SOA. Evidence of acid-catalyzed heterogeneous chemistry, characterized by greater contribution of higher molecular weight fragments to the SOA and corresponding changes in “Δ” patterns, is observed in the ozonolysis of α-pinene. Mass spectra of SOA formed during photooxidation of m-xylene exhibit features consistent with the presence of furandione compounds and nitro organics. This study demonstrates that mixtures of SOA compounds produced from similar precursors result in broadly similar AMS mass spectra. Thus, fragmentation patterns observed for biogenic versus anthropogenic SOA may be useful in determining the sources of ambient SOA

Gas-phase products and secondary aerosol yields from the ozonolysis of ten different terpenes

The ozonolyses of six monoterpenes (α-pinene, β-pinene, 3-carene, terpinolene, α-terpinene, and myrcene), two sesquiterpenes (α-humulene and β-caryophyllene), and two oxygenated terpenes (methyl chavicol and linalool) were conducted individually in Teflon chambers to examine the gas-phase oxidation product and secondary organic aerosol (SOA) yields from these reactions. Particle size distribution and number concentration were monitored and allowed for the calculation of the SOA yield from each experiment, which ranged from 1 to 54%. A proton transfer reaction mass spectrometer (PTR-MS) was used to monitor the evolution of gas-phase products, identified by their mass to charge ratio (m/z). Several gas-phase oxidation products, formaldehyde, acetaldehyde, formic acid, acetone, acetic acid, and nopinone, were identified and calibrated. Aerosol yields, and the yields of these identified and calibrated oxidation products, as well as many higher m/z oxidation products observed with the PTR-MS, varied significantly between the different parent terpene compounds. The sum of measured oxidation products in the gas and particle phase ranged from 33 to 77% of the carbon in the reacted terpenes, suggesting there are still unmeasured products from these reactions. The observations of the higher molecular weight oxidation product ions provide evidence of previously unreported compounds and their temporal evolution in the smog chamber from multistep oxidation processes. Many of the observed ions, including m/z 111 and 113, have also been observed in ambient air above a Ponderosa pine forest canopy, and our results confirm they are consistent with products from terpene + O_3 reactions. Many of these products are stable on the timescale of our experiments and can therefore be monitored in field campaigns as evidence for ozone oxidative chemistry

Contribution of First- versus Second-Generation Products to Secondary Organic Aerosols Formed in the Oxidation of Biogenic Hydrocarbons

Biogenic hydrocarbons emitted by vegetation are important contributors to secondary organic aerosol (SOA), but the aerosol formation mechanisms are incompletely understood. In this study, the formation of aerosols and gas-phase products from the ozonolysis and photooxidation of a series of biogenic hydrocarbons (isoprene, 8 monoterpenes, 4 sesquiterpenes, and 3 oxygenated terpenes) are examined. By comparing aerosol growth (measured by Differential Mobility Analyzers, DMAs) and gas-phase concentrations (monitored by a Proton Transfer Reaction Mass Spectrometer, PTR-MS), we study the general mechanisms of SOA formation. Aerosol growth data are presented in terms of a “growth curve”, a plot of aerosol mass formed versus the amount of hydrocarbon reacted. From the shapes of the growth curves, it is found that all the hydrocarbons studied can be classified into two groups based entirely on the number of double bonds of the hydrocarbon, regardless of the reaction systems (ozonolysis or photooxidation) and the types of hydrocarbons studied:  compounds with only one double bond and compounds with more than one double bond. For compounds with only one double bond, the first oxidation step is rate-limiting, and aerosols are formed mainly from low volatility first-generation oxidation products; whereas for compounds with more than one double bond, the second oxidation step may also be rate-limiting and second-generation products contribute substantially to SOA growth. This behavior is characterized by a vertical section in the growth curve, in which continued aerosol growth is observed even after all the parent hydrocarbon is consumed

Particle Phase Acidity and Oligomer Formation in Secondary Organic Aerosol

A series of controlled laboratory experiments are carried out in dual Teflon chambers to examine the presence of oligomers in secondary organic aerosols (SOA) from hydrocarbon ozonolysis as well as to explore the effect of particle phase acidity on SOA formation. In all seven hydrocarbon systems studied (i.e., α-pinene, cyclohexene, 1-methyl cyclopentene, cycloheptene, 1-methyl cyclohexene, cyclooctene, and terpinolene), oligomers with MW from 250 to 1600 are present in the SOA formed, both in the absence and presence of seed particles and regardless of the seed particle acidity. These oligomers are comparable to, and in some cases, exceed the low molecular weight species (MW < 250) in ion intensities in the ion trap mass spectra, suggesting they may comprise a substantial fraction of the total aerosol mass. It is possible that oligomers are widely present in atmospheric organic aerosols, formed through acid- or base-catalyzed heterogeneous reactions. In addition, as the seed particle acidity increases, larger oligomers are formed more abundantly in the SOA; consequently, the overall SOA yield also increases. This explicit effect of particle phase acidity on the composition and yield of SOA may have important climatic consequences and need to be considered in relevant models