Optical, physical and chemical characteristics of Australian continental aerosols: results from a field experiment

Radhi, M.; Box, Michael A.; Box, G. P.; Mitchell, Rosalind; Cohen, David D.; Stelcer, Eduard; Keywood, Melita

doi:10.5194/acp-10-5925-2010

Cited by 35 publications

(45 citation statements)

References 63 publications

(68 reference statements)

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“…Aerosol sources contributing to the noted rise during spring are heterogeneous, with suggested contributions from fine aeolian dust , a combination of biomass burning smoke, fine dust, and maritime aerosol from long-range transport (Radhi et al, 2010), and exogenous biomass burning aerosol originating in southern Africa or even South America (Rosen et al, 2000).…”

Section: Amplitude and Phase Of The Aerosol Optical Depth Of Harmonicmentioning

confidence: 99%

The Climatology of Australian Aerosol

2017

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Abstract. Airborne particles or aerosols have long been recognised for their major contribution to uncertainty in climate change. In addition, aerosol amounts must be known for accurate atmospheric correction of remotely sensed images, and are required to accurately gauge the available solar resource. However, despite great advances in surface networks and satellite retrievals over recent years, longterm continental-scale aerosol data sets are lacking. Here we present an aerosol assessment over Australia based on combined sun photometer measurements from the Bureau of Meteorology Radiation Network and CSIRO/AeroSpan. The measurements are continental in coverage, comprising 22 stations, and generally decadal in timescale, totalling 207 station-years. Monthly climatologies are given at all stations. Spectral decomposition shows that the time series can be represented as a weighted sum of sinusoids with periods of 12, 6 and 4 months, corresponding to the annual cycle and its second and third harmonics. Their relative amplitudes and phase relationships lead to sawtooth-like waveforms sharply rising to an austral spring peak, with a slower decline often including a secondary peak during the summer. The amplitude and phase of these periodic components show significant regional change across the continent. Fits based on this harmonic analysis are used to separate the periodic and episodic components of the aerosol time series. An exploratory classification of the aerosol types is undertaken based on (a) the relative periodic amplitudes of the Ångström exponent and aerosol optical depth, (b) the relative amplitudes of the 6-and 4-month harmonic components of the aerosol optical depth, and (c) the ratio of episodic to periodic variation in aerosol optical depth. It is shown that Australian aerosol can be broadly grouped into three classes: tropical, arid and temperate. Statistically significant decadal trends are found at 4 of the 22 stations. Despite the apparently small associated declining trends in mid-visible aerosol optical depth of between 0.001 and 0.002 per year, these trends are much larger than those projected to occur due to declining emissions of anthropogenic aerosols from the Northern Hemisphere. There is remarkable long-range coherence in the aerosol cycle across the continent, suggesting broadly similar source characteristics, including a possible role for intercontinental transport of biomass burning aerosol.

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Section: Amplitude and Phase Of The Aerosol Optical Depth Of Harmonicmentioning

confidence: 99%

The Climatology of Australian Aerosol

2017

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“…Almost all published experimental studies on CCN activity of fresh dust (e.g., Koehler et al, 2009;Herich et al, 2009) parameterize laboratory observations using the KT framework on the assumption that dust CCN activity is controlled solely by the amount of soluble salts in the mineral aerosol, with the insoluble fraction not affecting water activity. However, studies that measured soluble ions composition on dust samples collected from various dust source regions (e.g., Song et al, 2005;Radhi et al, 2010) indicated negligible amounts of soluble salts. In a recent study, Kumar et al (2011) compared the power law exponent derived from the experimental s c −D dry relationship with those determined from FHH-AT and KT, and suggested that FHH-AT is a better representation than KT for CCN activity of dry generated dust devoid of a soluble fraction.…”

Section: Introductionmentioning

confidence: 99%

Cloud condensation nuclei activity and droplet activation kinetics of wet processed regional dust samples and minerals

2011

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Abstract. This study reports laboratory measurements of particle size distributions, cloud condensation nuclei (CCN) activity, and droplet activation kinetics of wet generated aerosols from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. The dependence of critical supersaturation, s c , on particle dry diameter, D dry , is used to characterize particle-water interactions and assess the ability of Frenkel-Halsey-Hill adsorption activation theory (FHH-AT) and Köhler theory (KT) to describe the CCN activity of the considered samples. Wet generated regional dust samples produce unimodal size distributions with particle sizes as small as 40 nm, CCN activation consistent with KT, and exhibit hygroscopicity similar to inorganic salts. Wet generated clays and minerals produce a bimodal size distribution; the CCN activity of the smaller mode is consistent with KT, while the larger mode is less hydrophilic, follows activation by FHH-AT, and displays almost identical CCN activity to dry generated dust. Ion Chromatography (IC) analysis performed on regional dust samples indicates a soluble fraction that cannot explain the CCN activity of dry or wet generated dust. A mass balance and hygroscopicity closure suggests that the small amount of ions (from low solubility compounds like calcite) present in the dry dust dissolve in the aqueous suspension during the wet generation process and give rise to the observed small hygroscopic mode. Overall these results identify an artifact that may question the atmospheric relevance of dust CCN activity studies using the wet generation method.Correspondence to: A. Nenes (athanasios.nenes@gatech.edu) Based on the method of threshold droplet growth analysis, wet generated mineral aerosols display similar activation kinetics compared to ammonium sulfate calibration aerosol. Finally, a unified CCN activity framework that accounts for concurrent effects of solute and adsorption is developed to describe the CCN activity of aged or hygroscopic dusts.

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“…Australian dust particle size and colour is different from the Northern Hemisphere 'dust belt' (Kiefert et al, 1996;Qin and Mitchell, 2009;Radhi et al, 2010). For example, a greater fraction of larger particles has been found for Australian dust compared to African dust (Kiefert et al, 1996), suggesting that the optical properties of dust from Australia are different from the Sahara.…”

Section: Introductionmentioning

confidence: 94%

“…Recent field campaigns for identifying mineral composition of Australian dust (e.g. Qin and Mitchell, 2009;Radhi et al, 2010) have also contributed. Lake Eyre Basin of central eastern Australia is the most important source of mineral dust in the Southern Hemisphere, with an average of 82 dusty days per year (Bullard and McTainsh, 2003).…”

Section: Introductionmentioning

confidence: 99%

“…Using a cluster analysis of AErosol RObotic NETwork (AERONET) retrievals, Qin and Mitchell (2009) identified strong absorption of radiation by Australian dust compared to the 'dust belt' of the Northern Hemisphere. By conducting a field experiment, Radhi et al (2010) investigated optical, physical and chemical characteristics of Australian dust. Their mineralogical analysis indicates that the iron content of Australian dust is higher than other major sources of dust in the Northern Hemisphere, similar to the results of Qin and Mitchell (2009).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Simulation of the spatial distribution of mineral dust and its direct radiative forcing over Australia

Alizadeh¹,

Zawar-Reza²,

Sturman³

2013

Tellus B: Chemical and Physical Meteorology

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A B S T R A C T Direct radiative forcing by mineral dust is important as it significantly affects the climate system by scattering and absorbing short-wave and long-wave radiation. The multi-angle imaging spectro radiometer (MISR) and cloudÁaerosol lidar with orthogonal polarisation (CALIOP) aerosol data are used to observe mineral dust distribution over Australia. In addition, the weather research and forecasting with chemistry (WRF/Chem) model is used to estimate direct radiative forcing by dust. At the surface, the model domain clear-sky shortwave and long-wave direct radiative forcing by dust averaged for a 6-month period (austral spring and summer) was estimated to be (0.67 W m (2 and 0.13 W m (2 , respectively. The long-wave warming effect of dust therefore offsets 19.4% of its short-wave cooling effect. However, over Lake Eyre Basin where coarse particles are more abundant, the long-wave warming effect of dust offsets 60.9% of the short-wave cooling effect. At the top of the atmosphere (TOA), clear-sky short-wave and long-wave direct radiative forcing was estimated to be (0.26 W m (2 and (0.01 W m (2 , respectively. This leads to a net negative direct radiative forcing of dust at the TOA, indicating cooling of the atmosphere by an increase in outgoing radiation. Shortwave and long-wave direct radiative forcing by dust is shown to have a diurnal variation due to changes in solar zenith angle and in the intensity of infrared radiation. Atmospheric heating due to absorption of shortwave radiation was simulated, while the interaction of dust with long-wave radiation was associated with atmospheric cooling. The net effect was cooling of the atmosphere near the surface (below 0.2 km), with warming of the atmosphere at higher altitudes.

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Optical, physical and chemical characteristics of Australian continental aerosols: results from a field experiment

Cited by 35 publications

References 63 publications

The Climatology of Australian Aerosol

The Climatology of Australian Aerosol

Cloud condensation nuclei activity and droplet activation kinetics of wet processed regional dust samples and minerals

Simulation of the spatial distribution of mineral dust and its direct radiative forcing over Australia

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