The number of official "blue sky days" in Beijing declined in the first half of 2010, after several years of improvement, the Xinhua news agency reported. China's capital uses a 500-point scale to measure air pollution, and any score at or below 100 counts as "blue sky." (Above 100, the air is classified as "unhealthy" to various degrees.)
Last year, there were 146 blue-sky days in the first half of the year; this year, the number fell to 140. The city's environmental protection bureau blamed the increase on more "sandy-dusty weather" this past spring.
Here are two pictures taken from the same window on different days in May of this year. The second one is zoomed in more, because there were things to zoom in on.