Editor's note: The following was translated and edited from an article that appeared on the Sina.com blog of China National Geography magazine. In it, a Chinese science writer points out that even though residents still refer to it majestically as a "fog capital", true meteorological fog in Chongqing has actually decreased since industrialization. Scientists believe that industrial smog has simply taken its place.

Fog has long been a source of artistic inspiration in China. Just think of the mists in traditional Chinese painting and poetry: faint, indistinct, shapeless, mysterious. But somehow, at some point, fog began drifting away from us, and in its place came something else: pollution, smog… "haze". Which is it that we see drifting over our metropolises, and what does it have to do with this PM2.5 we've been hearing so much about lately?

A source of inspiration, wonder, and local pride

The city of Rui'an, Zhejiang Province seems normal enough, but on certain days it becomes a magical place with buildings peeping in and out of the mist, disappearing and reappearing like mirages. In ancient China, poets and writers would have sung the praises of a scene like this; today our first reaction is "Wait, is that fog or smog? What's it going to do to my lungs?"

In my childhood memories, fog was a thing of wonder. In the morning the fog would roll in silently, and the road to school that used to be so familiar became—in a matter of moments—strange, blurry, hazy. I could barely make out my classmates ahead of me, though I could hear them laughing: "We're pixies! We're in heaven!" We associated the mist with cartoons and stories; when it came it turned our world into a fantasy world of endless joy and imagination.  

Aside from the misty mountaintops, there's another spot in China famous for fog: the cloudy metropolis of Chongqing. I remember once asking a friend from Chongqing what time of year Chongqing is usually foggy, and he thought for a while then laughed: "Actually what I want to know is when Chongqing isn't foggy!" Then he told me, proudly: "Shanghai has the night, Beijing has autumn, Guilin has rain, and Chongqing has fog. Chongqing is most beautiful in the mist, and China's most beautiful mist is in Chongqing." Indeed, the fog does seem to smooth out the city's rough edges, transforming it into a peaceful watercolor of a city.

Chongqing's reputation for fog has a reasonable enough geographical explanation. Located on the east side of the Sichuan basin, surrounded by mountains, hot air, slow winds, and the confluence of two rivers, Chongqing has the perfect laboratory conditions for an excess of condensation.

A "mist"-understanding?　　

My friend's description of Chongqing inspired me to delve deeper. I began collecting all the information I could about China's "fog capital".

It didn't take long to dig up some data online: "Chongqing gets an average of 104 days of fog; compare that to London's 94 days a year or Tokyo's 55 days a year." In the 1950's, Chongqing got an average of 103 days of fog per year, or about once every four days. So it would seem that Chongqing has always deserved its foggy nickname. But then I found some conflicting information: In the past 50 years, Chongqing's fog has decreased, going down to around 50 days a year in the 70's and 80's, then down to 30-40 days a year in the 90's. In 2003, then-vice-director of the Chongqing Meteorological Administration Ma Li said in an interview with the Xinhua News Agency that fog needs a certain amount of suspended matter in the atmosphere to form, but according to results of a study in 2001, suspended matter had grown by as much as 2.7 times since 1990, leading to an oversaturation of suspended matter and a scattering of vapor particles, resulting in less overall fog.

Since at least the 1940s, Chongqing residents have been proud of their city's reputation for fog. But did you know that "fog capital" might actually be a misnomer? Some scientists believe Chongqing's industrial smog might be "clouding" the issue.

This prompted me to ask my friend again: "Do you feel like the fog has decreased?" "No!" he answered, "It's foggy pretty much every day." Apparently the Meterological Administration disagrees, so what's going on? What is this "fog" that my friend is so sure he sees practically every day?

"Scientific recognition takes time…"

The real question is, is it smog or fog? The meteorological definition of fog is: large amounts of tiny water or ice particles suspended in air at a low elevation, caused by condensed water, causing low visibility (less than 1 km). This is fog in the strict sense of the word. But it also has a more poetic definition: "Clouds are fog in the sky, fog is clouds on land" ("云是飘在天上的雾，雾是落在地上的云"). One could say that fog and clouds are children of the same mother, just called different things depending on their elevation.

"Large amounts of dry, microscopic dust or other particles suspended in the air, reducing visibility to less than 10 km, causing distant objects to appear yellow or red, and dark objects to appear blue." This is the Chinese Meteorological Administration (CMA)'s definition of the common Chinese word for smog/haze, "霾" (mái), a character which in ancient times referred to sand or dust in the wind, but which in modern times includes industrially-produced particulate matter. A report published in 2010, gives a stricter definition: "When visibility less than 10 km cannot be explained by factors like precipitation, sand storms, dust storms, or floating dust, and humidity is less than 80%, the phenomenon can be labeled as smog". So the biggest difference between fog and smog is humidity: over 95% and it's fog, under 80% and it's smog. The gray area between 80%-95% is a mixture of both, but mostly smog. In that case, is the "fog" capital" of Chongqing really a "smog" capital?

Researcher Wu Dui at the CMA's Guangzhou Tropical Oceanic Meteorological Institute had some unfortunate news for me: "Chongqing's reputation of a ‘fog capital' is actually a misnomer. Because Chongqing became a center of industry after the war, it's had severe air pollution ever since. But back then, science wasn't developed enough to know what to call it, and people thought it was just fog. London is the same way, after the industrial revolution it became a ‘smog capital' too. Scientific recognition takes time; in the past we simply thought low visibility was all due to fog; in reality it's quite often due to smog."

Source: sina.com.cn

Warning：The use of any news and articles published on eChinacities.com without written permission from eChinacities.com constitutes copyright infringement, and legal action can be taken.

Keywords: China pollution smog vs fog China Chongqing smog China PM2.5