Modeling Liquid Water Content of Atmospheric Aerosols

Kajino, M. (2003). Modeling Liquid Water Content of Atmospheric Aerosols. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-03-046

Preview

Text IR-03-046.pdf Download (257kB) | Preview

Abstract

The contribution of liquid water to measure aerosol was assessed using a numerical approach for European measurement data. Aerosol mass is usually determined after conditioning of the filter under dry condition for a predefined period according to a standard procedure. However, we find that the equilibrium of aerosol is not fully established and water is not completely evaporated after the conditioning.

In order to estimate the aerosol humidity, a mass transfer coefficient was derived for evaporating from filters. DAta from actual measurements of aerosol humidity were applied with a numerical kinetic approach, using the thermodynamic equilibrium as a boundary condition. The calculated coefficient ranges from 10-5 to 10-4 with an average value of 10-4.49.

Using this average value the expected water content of aerosol was assessed for a site in Austria. In a data set covering one year with daily samples, water contributed to the total amss between 0.00 percent and 35.9 percent with an average value of 4.1 percent. Most of the samples contained between one and two percent water, according to the calculations. In winter the air is humid and the concentration of inorganic hygroscopic compunds is also high, and so the amount of water uptake from the air is high. Under such conditions more than half of unidentified components is considered to be water. In summer the amount of hygroscopic components as well as relative humidity is low, water then yields only 8.8 percent of unidentifiedcomponents. According to the model calculations, it takes about 30 hours on annula average until 95 percent of the initial amount of water uptake is evaporated on the filter and even longer in winter.

The average water content at 49 sites of EMEP in 1999 after conditioning for 48 hours ranges from 0.54 ug m-3 to 3.8 ug m-3, that is 2.6 percent to 18.2 percent to total aerosol mass, while the mass trnasfer coefficient varies from 10-4 to 10-5.

Actions (login required)

View Item