Post-airpocalypse: Before and after photos of Beijing's 'smog season'

Residents of China's capital are enjoying some much-needed respiratory respite this week, as suffocating smog finally subsided to clear blue skies.

In mid-December, for just the second time ever, Beijing issued a red alert for air pollution - warning of severe smog expected to last more than 72 hours.

The measures to combat the red alert were extensive. Traffic was cut in half when a new number-plate system was introduced, forcing odd-numbered cars off the road one day and even numbered plates the next. Meanwhile, workplaces and schools were shut and industrial plants operated under limited production.

Fortunately for Beijing's 21 million citizens, a breath of cold air lifted the blanketing smog from the gasping city earlier this week.

Below are some images that demonstrate the stark contrast, a tale of two cities, between Beijing under 'airpocalypse' and Beijing under azure skies.