Introduction
As part of the
2004 intensive Pearl River Delta measurement campaign,
Raman lidar and Sun photometer observations were performed in
October-November 2004 to characterize the optical properties of
anthropogenic haze in the southern coastal region of the Guangdong
province close to the south coast of China. The field site was
chosen at Xinken (22.6° N, 113.6° W) which is
located at the Pearl River, about 80 km northwest of the center of
Hong Kong, 60 km southwest of Guangzhou, and 50 km west of
Shenzen. The Guangdong province is one of the fastest growing
economical centers in China. 40-50 million people live in the
Pearl River Delta (PRD) region (about 250 km x 250 km) at
the south coast of China.
The chemical composition of the aerosol in that area (including
Hong Kong) has recently been analyzed in detail.
The haze mainly consists of particles from fossil fuel consumption
and biomass burning. Minor contributions result from regional and
long-range transport of dust (including road dust) and sea breeze
effects (maritime particles). The climate-relevant optical
properties of the haze, a mixture of young and well-aged
particles, have not been quantified yet. More generally speaking,
column and height-resolved observations of aerosol optical
properties in the subtropical region of east Asia are very limited.
Such observations are, however, urgently needed for
a realistic estimation of the climatic impact of present and
future states of aerosol pollution in eastern Asia.
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Measurements
For the first time, Raman lidar observations of aerosol
optical properties were conducted in China. The portable
Raman lidar Polly
separately
measures profiles of the volume extinction and backscatter
coefficients of the particles, and thus the respective
extinction-to-backscatter ratio at 532-nm wavelength
during nighttime. At daytime, when Raman
signals cannot be detected, the lidar delivers profiles
of the particle backscatter coefficient only. The automatic
Sun photometer, on the
other hand, continuously records aerosol optical depths
with high spectral resolution (about 10 aerosol channels)
from 351–1063 nm during daytime. Optical depth
uncertainties are of the order of 0.01–0.03.
Discussion
Raman lidar and Sun photometer observations
at Xinken, Pearl River Delta (22.6° N, 113.6° E),
near the south coast of China in October 2004 revealed
high values of aerosol optical depth of, on average, 0.91
at 532-nm wavelength. Column-averaged particle extinction
coefficients of up to 800 Mm-1 were found in
the haze layer that typically reached up to 1.5–3 km
height. Lidar ratios (mainly 40–60 sr) and Angström
exponents (around 1 for the 381–502-nm and 1.2 for the
502–1046-nm spectral range) indicate comparably large
and considerably absorbing particles (effective radius of
about 0.3 µm, single scattering albedo of 0.85–0.9) that
mainly originate from industrial and biomass-burning
emissions. The observed high aerosol optical depth in
the Guangdong province, one of the fasted growing economic
centers of China, is in agreement with the expected
1990–2005 pollution trend, derived from 1960–
1990 observations of aerosol optical depth.
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