Concentration and size distribution of atmospheric particulate matter on a forested area in the basque country (Spain).

Abstract

Throughout the period going from October 1989 to September 1990, we measured the air concentrations of both SO₂ gas and of the atmospheric particulate fraction, both in total and split into in size ranges, by means of a Denuder‐filter system and of a cascade impactor, respectively, all of it for a forested area located in the centre of the Basque Country in northern Spain.

The results thrown when the Denuder‐filter system was used, show the SO₄ ^2‐and NH₄ ⁺ ions, with 4.6 μg m^‐3 of each, as being the most important species in the particulate fraction, whereas the NO₃ ^‐ ion would come second in the scale, with 0.9 μg m^‐3. The average concentration of SO₂ gas was 3.2 μg m^‐3.

The levels of SO₂ gas and those of the SO₄ ^2‐ ion, both calculated for Summer and Winter, are related in such a way that their correlation shows the considerable effect of local emissions on the actual air concentrations for both species during the Winter season. Likewise, after an assessment of the above correlation, according to the backtrajectory followed by the air mass, we infer that the greatest correlation for both these species is given by those air masses coming from the NW,

The characteristic anthropogenic ions, SO₄ ^2‐ and NH₄ ⁺, actually appear as part of the fine particles (D < 0.73 μm), whereas the CI^‐ and Na⁺ marine ions, together with the Ca²⁺ terrigenous ion, are part of the coarse particles (D = 0.73 ‐ 4.21 μm).

On the other hand, the NO₃ ^‐ ion is found in both fine and coarse particles (D = 0.45 ‐ 4.21, μm), which is probably due to the absorption of HNO₃ gas (as a result of nitrogen oxides emission) in the basic coarse particles.

Key words:

• Aerosol
• atmospheric particulate fraction
• size distribution
• denuder‐filter system
• cascade impactor.