Non-dust Periods Research Articles

Chemical Composition Change in TSP Due to Dust Storm at Gosan, Korea: Do the Concentrations of Anthropogenic Species Increase Due to Dust Storm?

Aerosol composition change between dust storm and non-dust storm periods in spring is studied using the total suspended particle data measured at Gosan, a background area in Korea. The concentrations of eight inorganic ions and 12 elements were analyzed for the TSP samples collected from March 1992 to May 2006. Two-step statistical analyses were carried out for the data: F test and t test. The concentrations of anthropogenic ionic species showed increasing trend since 2003. The absolute concentrations of most anthropogenic species such as sulfate or nitrate increased (from 7.33 to 9.25 µg m−3 and from 2.04 to 4.84 µg m−3, respectively) during the dust storm period. However, the enrichment factors or normalized concentrations based on Al of most anthropogenic species decreased during dust storm period (factor of 0.1–0.5). It suggests that, in general, relative importance of anthropogenic species during dust storm would be not high.

Photometric measurements of spring aerosol optical properties in dust and non-dust periods in China

Aerosol observational data spanning three years (2005–2007) from the Chinese Sun Hazemeter Network (CSHN) were analyzed to characterize the optical properties of spring aerosol particles in dust and non-dust weather conditions. The measurements were segregated and the dates of dust period were chosen by ground-based observations and the National Sand-dust Weather Almanac. Observational data obtained under suitable weather conditions and averaged over 15 sites in the CSHN. The data indicated that the mean spring aerosol optical depth (AOD) increased by 33% in dust weather than in non-dust weather over the three years under study. Further, the angstrom exponent ( α) decreased by 24% in dust weather compared to in non-dust weather. At dust-source sites, AOD increased by 31% and α decrease by 20%. The atmosphere of dust-source sites is relatively clean, and is generally only contaminated with small quantities of dust particles. Atmospheric aerosols of this region were primarily in the form of coarse mode. Aside from being influenced by dust storms, the atmosphere of both near-source and distant sites displayed a large proportion of man-made aerosols, resulting in a large increase in the AOD and α values. Due to the contribution of sand-dust, the AOD of near-source and distant sites increased by 53% and 23%, respectively, while the value of α was reduced by 22% and 25%, respectively. Due to the content differences of man-made aerosols, and the fact that some observational data cannot be obtained under heavy dust storm weather conditions, the mean AOD and α were highest at distant sites (0.69 and 0.91), intermediate at near-source sites (0.51 and 0.86), and lowest at the dust-source sites (0.36 and 0.48). In addition, if we take into account the impact of strong dust storms in which AOD can't be observed by sunphotometer, the AOD probably become greater the farther form the dust-source region in non-dust periods, and while it is opposite in dust periods. Data were also obtained for both urban and ecology background sites. AOD and α values were both significantly higher at urban sites than at neighboring natural ecology background sites during both dust and non-dust periods, but the occurrence of dust process made the multiplier slightly larger.

Number size distribution of atmospheric aerosols during ACE-Asia dust and precipitation events

Measurements of size-resolved particle number concentrations during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) field campaign were made at the Gosan super-site, South Korea. In East Asia, dust and precipitation phenomena play a crucial role in atmospheric environment and climate studies because they are major sources and sinks of atmospheric aerosols, especially in the springtime. Total Ozone Mapping Spectrometer (TOMS) Aerosol Index and backward trajectories are analyzed to investigate the spatial and temporal evolution of dust storms. The size distributions between dust and non-dust periods and times with and without precipitation are compared. In order to understand the temporal evolution of the aerosol size distribution during dust and precipitation events, a simple aerosol dynamics model is employed. The model predicted and observed size distributions are compared with the measured data. The results show that the coarse mode particle number concentrations increase by a factor of 10–16 during dust events. During precipitation, however, particles in the coarse mode are scavenged by impaction mechanism. It is found that the larger particles are more efficiently scavenged. The degree of scavenged particle varies depending on the rainfall rate, raindrop size distribution and aerosol size distribution.

Size distributions of aerosol number concentrations and water-soluble constituents in Toyama, Japan: A comparison of the measurements during Asian dust period with non-dust period

Size-separated aerosol number concentrations and water-soluble constituents were measured in Toyama, the Hokuriku district, near the coast of the Japan Sea, during the spring and summer in 2003. The number concentrations of coarse particles were significantly high in April, which was due to Asian dust events called Kosa in Japanese. Particulate nssCa 2+, which is mostly present in the coarse-mode particles, was significantly high in April. On the other hand, the concentrations of NH 4 + and nssSO 4 2−, which mainly exist as the accumulation-mode particles were not high in April. The mass-size distributions of water-soluble constituents were compared with the size-separated number concentrations of particles. Backward trajectory analysis was also employed to examine the transport process of the air mass in Toyama.

Characteristics of aerosols collected in central Taiwan during an Asian dust event in spring 2000

Aerosol samples for PM 2.5 and PM 2.5–10 were collected at four locations in central Taiwan from 26 to 31 March 2000, a period that experienced exceedingly high PM levels from 29 to 30 March due to the passage of an Asian dust storm. The samples were analyzed for mass, metallic elements, ions, and carbon. The purpose of this paper is to investigate the influence of the dust storm on the characteristics of local ambient particulate matter. The results indicate that the concentrations of the crustal elements Ca, Mg, Al, Fe and the sea salt species Na + and Cl − in PM 2.5–10 during the dust episode exceed the mean concentrations in the non-dust period by factors of 3.1, 2.9, 2.6, 2.2, 2.3 and 2.1 respectively. Enrichment factors of Ca, Fe, and Mg in PM 2.5–10 during the dust event are close to unity, indicating that these elements are from soil. Reconstruction of aerosol compositions revealed that soil of coarse particulates elevated approximately 50% in the dust event. It is noted that during the dust event, the ratio of Mg/Al in PM 2.5–10 ranged from 0.21 to 0.25 while that of Ca/Al ranged from 0.6 to 0.9, levels more constant than those obtained in non-dust period.

An X-ray photoelectron spectroscopy study of elements on the surface of aerosol particles

Total suspended particulate (TSP) samples were collected at three sites, before and during a major dust storm in March, 2002. For comparison, PM 10 (particulate matter with aerodynamic diameters less than 10 μ m ) were collected at one of the three sites. X-ray photoelectron spectroscopy (XPS) was employed to analyze the surface composition and iron species on aerosol particles. Results were compared with bulk analysis using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). It was shown that aluminium and cadmium were present as Al 2O 3 and CdO on particle surfaces. The majority of lead was in the form of PbSO 4, while carbonate or oxide was the major species of zinc. Sulfate was the main compound of sulfur. It was found that surface iron species were the most complex ones. The curve fitting of Fe 2p peaks showed that the main existing forms of surface iron were oxide, sulfate, silicate and phosphate, with some compounds adhering to SiO 2 and/or Al 2O 3 particles. The surface atomic ratio of Fe to Al on aerosol particles had a good correlation with its bulk ratio. The surface ratio of S to Al in pre-storm samples were higher than in storm ones, suggesting that sulfur was substantially enriched on particle surface during non-dust period. It is speculated that surface S plays a role in reducing surface Fe (III) to Fe (II).

Ground observations of a strong dust storm in Beijing in March 2002

On 20 March 2002, one of the most intense dust storms of the last decade struck Beijing: the total suspended particle (TSP) mass concentrations during the event reached 12 mg/m3 and the visibility was reduced to less than 200 m. Variations in meteorological conditions in the boundary layer were monitored during the event, and changes in the physical properties and chemical composition of the aerosol also were studied. The dust storm was accompanied by a sharp and distinct increase in wind speed, a decrease in relative humidity, and increased mixing in the boundary layer due to turbulence. Back trajectory analysis and meteorological analysis showed that the main sources of dust particles that affected Beijing were most likely in southern Mongolia and the western part of Inner Mongolia, China. The amounts of Mg, Al, K, Ca, Ti, V, Cr, Mn, and Fe relative to one another were similar for the dust storm and nondust storm samples, and these elements occurred in near‐crustal proportions. In contrast, both the concentrations and enrichments relative to the crustal reference material for other elements, such as Se, Ni, Pb, Br, and Cu, were much higher during the dust storm than before or afterward. These elements, which are often associated with pollution emissions, apparently originated from distant sources upstream as well as from local sources in Beijing. Even though their enrichments were lower during the dust event, the concentrations of S, Zn, and Cl during the dust storm were higher than in the nondust periods; these results are further evidence that dusty air often contains higher levels of pollutants than nondusty air.

A comparison analysis of chemical composition of aerosols in the dust and non-dust periods in Beijing

Dust events occurred frequently in Beijing in recent years. In this work, 120 aerosol samples were collected in two typical dust events (21–22 March and 15 May) and a non-dust period in Beijing from March to May 2001. Samples were analyzed for major elemental components by the Proton Induced X-ray Emission (PIXE) method. Results show that the enrichment factors of crustal elements such as Mg, Al, and Ti had little differences between the dust period and the non-dust period in Beijing, while the enrichment factors of other elements that have a relation to anthropogenic emissions were very low during the dust period. The results derived by using multivariate factor analysis from the observation data show that the sources such as soil dust, industry, and fuel combustion were among the major contributors to the particles in Beijing.

Wavelength‐dependent aerosol single‐scattering albedo: Measurements and model calculations for a coastal site near the Sea of Japan during ACE‐Asia

Wavelength‐dependent optical properties together with the size‐resolved elemental and chemical composition of the atmospheric aerosol were measured at Yasaka, Japan, near Wakasa Bay on the coast of the Sea of Japan. Observations were performed as part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE‐Asia) campaign during three weeks in March and April 2001. Information about the detailed chemical composition and the size distribution of the aerosol, including absorbing material, was used to model optical properties of the aerosol and compare them with directly measured properties. Continuous, size‐resolved measurements of aerosol scattering and backscattering coefficients were made at wavelengths of 450, 550, and 700 nm. Aerosol size distribution measurements were taken three times during the campaign for a period of 3–4 days each, using cascade impactors. One of the measurement periods was influenced by an intense yellow dust event originating on the Asian continent (20–25 March 2001), while the other two data sets were only weakly influenced by dust particles. The size‐resolved measurement of aerosol scattering coefficients and the chemical analysis showed that the dust was accompanied by fine accumulation‐mode particles during the dust event. The effects of the mineral dust particles on the optical and chemical properties of the aerosol are discussed, and data sets with and without desert dust influence are compared. Before the optical closure calculation a mass closure of the aerosol was performed, and the influence of the nonanalyzed fraction on the calculated optical properties of the aerosol is investigated. In general, good agreement between measured and modeled aerosol optical properties was found for the aerosol scattering and absorption coefficients, while less agreement was found for the backscattering coefficients, especially for the coarse mode of the aerosol. A distinct difference between the dust and nondust periods was found for the wavelength‐dependent single‐scattering albedo.