Beijing: China's capital registered a boom in online orders for condoms and sportswear rather than masks and air purifiers, as the city of over 22 million people reeled under the first-ever red alert for rising levels of pollution.

While it is easy to imagine a sharp rise in online orders for anti-pollution products such as masks and air purifiers on smoggy days, a boom in the sales of condoms and sports-wear might be a little unexpected.

According to search ratings for last week, China's largest online shopping platform, searches for condoms were clearly correlated with those Chinese cities that had heavy smog.

Beijing has been engulfed for thick smog for several days in the past few weeks and the city's first-ever red alert was issued on Monday stating that air will remain foul till December 10.

In Beijing and some northern cities that were severely hit by smog, the rise in orders of condoms went beyond the sales in cities with cleaner air.

Interest in sportswear also increased during the heavy smog. Those cities with serious haze recorded more frequent searches for sportswear, as residents have a stronger willingness to exercise outside once the air gets cleaner.

Beijing has taken a series of emergency pollution controlrestrictions, ranging from closing industrial operations toreducing road traffic by half.