Comparability of low-volume PM10 sampler with β-attenuation monitor in background air

A field study was carried out to evaluate the performance of a continuous particulate monitor for measuring particulate matter PM10 at a low-concentration background air. The comparison was carried out using a LVS-PM10 reference sampler described in EN 12341:1998 Annex B1 and a β-attenuation particulate monitor Eberline FH 62 I-R. The field test site is situated in central Finland (62°35′N, 24°12′E). The experimental period was between 22 September and 5 December 2001 representing typical Finnish autumn and early winter weather conditions for the area. The comparison consisted of 42 parallel 24-h measurements. The PM10 mass concentration varied in the range 1.5–18 μgm−3 with an average of 5.1 μgm−3. The particulate monitor was found to be capable of measuring low concentrations down to 2 μgm−3 with an estimated measurement uncertainty of ±1 μgm−3. The PM10 concentrations measured by the monitor were close to the results of the gravimetric reference sampler giving slightly higher concentrations. The mean ratio (monitor/reference sampler) of all results was 1.06±0.12. When relative humidity was over 85% and daily temperature was below 0°C, the monitor results were systematically about 0.5 μgm−3 higher than the results of the reference sampler. In three cases when temperature suddenly decreased under freezing point, the concentration difference was as high as 2 μgm−3. Absorption of water on the particles was the most probable reason for the concentration difference. As a part of validation the main water-soluble inorganic ions of the PM10 samples were analyzed by ion chromatography. They accounted for about 40% of the measured PM10 mass concentration and the relative proportion of sulfate was the largest. The variation of the chemical composition seemed not to have noticeable effect on the comparability of the two methods.