Analysis on the Major Chemical Composition and the Estimation of Water Content in SPM collected in the Extensive and Highly Time-resolved Measurement during an Early-winter Severe Pollution Episode

Abstract

This paper describes the results of highly time-resolved measurement of Suspended Particulate Matter (SPM) conducted at five sites in the Kanto Plain, Japan, during the early-winter severe pollution episode in 1994. 2-hour averaged SPM samples were collected during the period of December 23-25, when the areal mean SPM concentration in the Kanto Plain was highest in fiscal year 1994. The sum of carbonaceous species (elemental carbon: EC, organic carbon: OC) and inorganic ionic species (Cl^-, NO₃^-, NH₄⁺, and SO₄^2-) accounted for most of the SPM mass concentrations except during the period of high relative humidity. Carbonaceous species contributed to about 50% of SPM mass concentrations. Major ionic species of CI^-, NO₃^-, and NH₄⁺were in the form of NH₄Cl and NH₄NO₃produced from gas-particle equilibrium reactions. In the central and western part of the Plain, the production of NH₄Cl and NH₄NO₃appeared to be controlled by the supply of NH₃. While in the northeastern part of the Plain the supply of HCl and HNO₃ may be the controlling factor in producing these particles.
The contribution of water, another major component of SPM, to the measured concentration by automated SPM monitors (β-ray absorption type) was investigated by operating two SPM monitors simultaneously, one of which was equipped with an aerosol drying tube at the air inlet. Readings from the SPM monitor equipped with the drying tube were systematically lower than those equipped with a dummy tube by up to 20%. To account for the water content in the measured SPM concentrations at the ambient air quality monitoring stations, the applicability of an aerosol swelling model based on Winkler's experimental formula was further examined.