Hygroscopic Growth of Tropospheric Particle Number Size Distributions over the North China Plain
The hygroscopic growth of atmospheric sub-µm particle size distributions
(diameter Dp ranging from 22 to 900 nm) was studied at a rural/suburban
site in the North China Plain within the framework of the international CAREBEIJING
research project. The goal was to characterize the regional aerosol
in the polluted North-Eastern Plain in China. Size descriptive hygroscopic
growth factors (DHGFs) were determined as a function relative humidity (RH)
by relating particle number size distribution at a dry condition (< 30%) to
those measured at higher RHs (RH = 56, 76, 85, and 91%). In the size range
of the accumulation mode (Dp > 100 nm), the DHGF are substantially higher
than in the Aitken particle mode (Dp < 100 nm) as a result of different chemical
composition. The strongly size-dependent behavior of the DHGF highlights
the relevance of particulate sulfate production over the North China
Plain from gas phase chemical reaction as well as by liquid phase processes
in convective clouds. Furthermore, all results concerning the DHGF show a
significant dependency on meteorological air masses. The hygroscopic growth
of accumulation mode particles correlates significantly with the PM1-mass
fraction of sulfate ions determined by chemical analysis. Finally, this investigation
provides a parameterization of the hygroscopic growth of 250 nm
particles, which might be useful when predicting visibility and radiative forcing,
and perform atmospheric aerosol model validations.
Created 2008-09-26 18:26:50 by Uwe Raffalski Last changed 2008-10-03 14:20:59 by Uwe Raffalski
