I spent last weekend touring the Washington National Arboretum, where a China Garden is expected to be built, and the Mormon temple in Kensington, Maryland, whose spikes seem to be piercing the sky and something that I have seen many times driving into Washington DC through Capital Beltway.

I clicked photographs of the Capitol Columns in the arboretum and the golden spikes of the temple from various angles. But something kept distracting me from admiring the beauty of structures. It was the blue sky with fluffy white clouds in the background, something common in DC but rare in Shanghai or Beijing.

Chinese visitors to the US no longer feel awed by the skyscrapers in New York City and the Metro tunnels which go so deep underground in DC; Shanghai's skyscrapers are actually taller now. Topped out last week, the 121-story, 632-meter Shanghai Tower will be the second tallest building in the world upon completion next year, surpassed only by the Burj Khalifa in Dubai.

Beijing and Shanghai both have extensive subway systems, mostly built in a short time span before the Beijing 2008 Olympic Games and the Shanghai 2010 World Expo. They are already among the longest in the world, surpassing the historic ones in London, Moscow and New York.

However, when you look out of the skyscrapers in Shanghai's Lujiazui or exit a subway station along Chang'an Avenue in Beijing, you will rarely see the kind of blue sky and white clouds I saw last weekend. In fact, I cannot remember the last time I saw a bright sun in Beijing. I like telling my Beijing friends and colleagues that it is often shrouded in smog, like a "salty egg yolk".

China's rapid modernization over the past more than three decades has narrowed much of the gap with the developed world. But it has sharply widened the gap on the environmental front. Before the reform and opening-up, which began in the late 1970s, China was an economy of scarcity. Many items, including cloth, were rationed. Now China supplies the world with a dazzling array of manufactured goods, and China-made garments clothe a good part of the world.