The challenge of improving visibility in Beijing Department of Atmospheric and Oceanic Science, School of Physics, Peking University, Beijing, China
Received: 18 December 2009 – Published in Atmos. Chem. Phys. Discuss.: 05 March 2010 Abstract. The "Blue Sky Project" was proposed in 1998 to investigate by how much
emissions should be reduced to increase blue sky frequency in Beijing, which
hosted the Summer Olympics in 2008. This paper focuses on the temporal
variation of visibility and its dependence on meteorological conditions and
suspended particles at Beijing using the hourly observed visibility data at
Beijing Capital International Airport (BCIA) from 1999 to 2007. It has been
found that about 47.8% (24.2%) of the hours in Beijing are "bad"
("good") hours with visibility below 10 km (equal or higher than 20 km)
between 1999 and 2007. Due to the high Relative Humidity (RH), summer is the
season with the lowest mean visibility in a year. Although PM10 index
was reported in a decreasing trend (Chan and Yao, 2008), the increase of RH
has resulted in a decreasing trend of visibility over BCIA in the summer
from 1999 to 2007. To ensure blue sky ("good" visibility) for Olympics
2008, daily mean PM10 index should have been reduced from 81 to 44.
This requires that not only vehicle emissions, but also other emissions
should be limited. Observations verify that blue-sky-hour rate increased
significantly after mean PM10 index was reduced to 53 during Olympics
2008, however, the visibility of 2009 returned to the mean level from 1999
to 2007 during the period 8−24 August. RH (aerosol)
contribute 24% (76%) of the improvement of visibility during August
Revised: 01 August 2010 – Accepted: 17 August 2010 – Published: 24 August 2010
Citation: Zhang, Q. H., Zhang, J. P., and Xue, H. W.: The challenge of improving visibility in Beijing, Atmos. Chem. Phys., 10, 7821-7827, doi:10.5194/acp-10-7821-2010, 2010.