Aerosol light-scattering coefficients and size distributions in a suburban area in Taiwan

J. Aerosol Sci. Vol. 29, Suppl. 1, pp.S651-S652, 1998 8 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0021~8502!98 $19.00 + 0.00

Pergamon

AEROSOL

LIGHT-SCATTERING

COEFFICIENTS

IN A SUBURBAN

AND SIZE DISTRIBUTIONS

AREA IN TAIWAN

C.T. LEE and J.J. TSAI National Central University, 38 Wu-chuan Li, Chungli, Taiwan 32054, ROC. KEYWORDS Atmospheric Aerosols; Aerosol Light-scattering Coefficients; Aerosol Size Distributions; Meteorological Factors; Visibility The scattering of atmospheric aerosols to solar radiation plays an important role in direct radiative forcing of climate. Atmospheric

aerosols were collected at Tainan in southern

Taiwan for 53 days in the springtime of 1997. An aerosol spectrometer (PMS model PCASPX) was used to measure aerosol size distribution,

and an Integrating Nephelometer

(TSI

model 3563) was set up to acquire aerosol light-scattering coefficient (crsp). The daily averages of (T,~sfrom green-wavelength

measured at Tainan were in the

range of 0.06 to 0.48 Km’. The results are consistent with those measured at other urban areas in the world. concentrations

Fig.1 shows the hourly

averages of (T,~s and aerosol

(C,,s) during this sampling period.

volume

In general, both asp and C, agree

moderately well with each other with a linear regression R2 of 0.79. Meanwhile, the asp is found to have a close relationship with meteorological factors in this work.

Fig.1. The hourly averages of aspsand aerosol volume concentrations (C,s). Fig. 2 exhibits a rapid increase of crspwhen relative humidity reaches 7%80% and above. This range of humidity

is consistent with the deliquescent point of hygroscopic aerosols.

Another finding indicates that wind speed exhibits an inverse relationship with asp in this work. S651

S652

Abstracts

-y E s Ef b ,h 2

0.9 0.8 0.7 0.6 0.5 04 0.3 0.2

g

O~'o

of the 5th International

Relative

Aerosol

Humidity

Conference

1998

(%)

Fig.2. Aerosol qps and environmental relative humidity.

The observed qps are in an excellent agreement (R2=0.97) with the calculated values by using the measured aerosol size distributions and with the application of Mie theory. Fig, 3 shows the size distribution

of cr,,s results from this calculation. The contribution of sub-

micron particles to cr,,s is around 88% and the peak diameter is in the range of 0.5 to 0.6 pm.

Fig.3. Aerosol crspsize distributions.

During the sampling period, visibility observation was made occasionally. In 370 hours with both the observed visibility and the measured asps, the relationship of visibility and asps is shown in Fig.4. The observed visibility exhibits an inverse relationship with the measured (T,~s,which apparently follows the definition of visual or meteorological range. -E

1.0

ii;:

Hourly

Visibility

(Km)

Fig. 4. The observed visibility and the measured (s,~s(number of data points is 370).

ACKNOWLEDGEMENTS The authors thank the National Science Council of the Republic of China on Taiwan for financially supporting this research under Contract No. NSC 86-2621-P-008-013.