Smog? There's an app for that 16 November 2013 Last updated at 00:58 By Celia Hatton BBC News, Beijing Here's a depressing fact about my life in smoggy Beijing: at our house, we have "pollution rules" dictating when our toddler is allowed to play outside. Monitors around the city give hourly readings indicating the levels of PM 2.5 particles, the tiny specks of chemical dust hanging in the air that are harmful when inhaled. According to the US embassy's Air Quality Index, a value of 50 represents good air quality with minimal threat to public health. But as any Beijinger can tell you, if we waited until the AQI dropped below 50, our daughter would only venture outside a few times a year. So my husband and I were forced to invent our own standards. If the PM 2.5 reading falls below 100, my daughter can take wobbly steps outside for as long as she likes. When the readings land between 100 and 200, then she can enjoy her beloved slides and swings once in the morning and once in the afternoon for no more than 15 minutes at a time. On days when the PM 2.5 reading shoots above 200, the playground is off limits. The sounds of The Wheels on the Bus, her favourite song, can only be heard alongside the constant whir of five air purifiers spread throughout our apartment. On the murkiest days, if my toddler wants to go beyond her protected bubble, she must go directly to another indoor play area, usually a neighbour's house. Luckily, when the air is foul, it's not difficult to find other desperate parents eager to distract their own captive children. Best of Beijing Admittedly, the rules are relatively arbitrary. And they probably don't protect my child from all of the harmful effects of pollution, or the guilt we feel when we're forced to keep her indoors. But now, something to partially alleviate our emotional stress: a free smog-forecasting mobile application that predicts when the capital will enjoy its next bout of clean air. Banshirne.com was built by Dustin Grzesik, a geophysicist by training, who constructed the app, his first, after analysing the city's weather patterns. "It's pretty clear if you live in Beijing and you get a northerly wind, the pollution clears up in most cases and I wanted a way to automate that," he said. So far only a few hundred are using the Android app, mostly cyclists who wanted a way to predict when they could schedule group outings. "It's to help make people make the best of Beijing," Dustin explains. Because when it's nice out, it's really a beautiful place to be. It's a huge boost to meet a huge group of people ready to ride. Think of Banshirne as Dustin's parting gift to a city he loves. He moved to San Francisco, partly to ensure a supply of clean air for his two-and-a-half-year-old son. "After looking at the data for the past year and living through the so-called 'airpocalypse' last winter, " Dustin says, referring to last January's bout of terrible pollution when the PM 2.5 levels hit 800, "we started thinking about whether we wanted to stick around and wait for things to get better or not. And we just decided for our son's sake that we didn't want to do that. I understand Dustin's troubles. For now, just predicting Beijing's next blue sky helps. If my daughter and I venture outside tomorrow at 05:00, Banshirne promises, we'll be treated to lungfuls of clean-ish air.