Collection efficiency of midget impinger for o-tolidine particles was determined with a newly developed particle generation system consisting of a glass nebulizer and a glass cylinder. To avoid contamination with toxic substances, 1 cm3 methanol solution of o-tolidine was nebulized and completely dried in the glass cylinder. The total amount of generated particles was controlled by generation time and the size distribution of aerosol particles was adjusted by varying the concentration of nebulised solution. The size distribution of particles was determined with an Andersen sampler followed by a high performance liquid chromatography analysis with ultraviolet or fluorescence detection. The mass median diameters (MMDs) of the generated particles were 0.40, 0.66 and 1.1 μm when the concentrations of nebulized solution were 0.01, 0.1 and 1 g dm-3, respectively. The geometric standard deviation was 2.0. The collection efficiency of midget impinger did not exceed 30 % when the MMD was 1.1 μm, and it was dependent on the particle size. It is concluded that the evaluation of aiborne particle concentration in working environment by means of the midget impinger is not valid when submicron particles are dominant.
In order to investigate on particulate matter emission and generation by the traffic of heavy-duty vehicles on roads, total suspended particulate matter (TSP) were collected at the roadside along major local-road Urawa-Tokorosawa with high-volume air samplers during September 14∼16 and November 30∼December 5, 1992. Concentration of tire-dust in TSP was determined by a method based on the determination of thiophene derivatives generated by the pyrolysis of TSP. During the latter sampling period, ambient concentrations of tire-dust generated by the traffic of heavy-duty vehicles and passenger cars were 1.8∼5.9 and 2.7∼6.0 μgm-3, respectively. These results suggest that 3-methylthiophene be a suitable indicator of TSP emitted and generated from heavy-duty vehicles, because it is a specific pyrolyzate from tire-dust for trucks and buses. Concentration of elemental carbon (EC), most of which could be emitted by diesel-powered vehicles. Contributions of total tire-dust by heavy-duty vehicles and passenger cars to TSP and EC concentration were ca. 4 and ca. 20%, respectively.
In order to characterize atmospheric aerosols of desert areas in China, various aerosol samples were collected during the periods of yellow sand episode and non-episode at Alashan and adjacent in the Inner Mongolia Autonomous Region and the Ningxia Autonomous Region. Water-soluble ion concentrations in the atmospheric aerosols, ion equivalent balance, acidity and buffering ability of size-segregated atmospheric aerosols were studied. The results showed that : (1) Ca2+, Na+ and SO42- ions were the main chemical components of atmospheric aerosols in the areas, and occupied about 70% and 20% in total cation, and about 70% in total anion, respectively; (2) the buffering ability (ΔCb) of aerosols in these areas was very high up to 1,730 neq/m3 even in the period of non-eqisode; (3) aerodynamic diameter of fine particles was smaller than 1.1 μm, the equivalent balances between cation and anion were apparent, and the predominance of cation was obvious for particles larger than 2.1 μm; (4) the peak of mass concentration of aerosols was in the size range of 2.00∼ 5.00 μm during the sand storm, which is equal to the aerodynamic diameter of particles observed for long distance transportation. Strong buf3fering ability and low acidity of the atmospheric aerosols may play a significance role in the neutralization of acidic aerosols during long-rang transportation and regional acid rain.