Hong Kong residents have been warned to stay indoors as particulate matter (PM) pollution reaches unhealthy levels. Plume Labs reached out to Karl, a Hong Kong resident who runs a local kindergarten. He explained the school’s daily battle to make the invisible, visible.

“Every year it’s the same in January and February,” Karl says. “It’s foggy. You can feel the heavy air.” Usually most of us don’t feel a significant difference, but children and older people are impacted more seriously when PM pollution gets high.

PM consists of small solid particles that float in the air and penetrate into our airways. The finest of these (named PM2.5) have a diameter of less than 2.5 microns and can even enter the bloodstream, increasing the risk of both cardiovascular and respiratory illnesses.

On Monday afternoon, PM2.5 levels reached 168 on the Plume AQI scale, indicating excessive pollution. This means that even healthy people may start showing negative symptoms after very short periods of exposure, even just a few minutes.

When levels are so high, the community is forced to take action. Karl received an email from his son’s school stating that outdoor activities had been moved indoors, and outdoor swimming classes were also cancelled.

He has to make similar decisions at his own school. “We’re very conscious of pollution and check air quality levels to see if the kids will be allowed out,” he says. Air quality forecasts help him make that call.

Such forecasting is a difficult task, drawing on machine learning algorithms to predict trends in areas without adequate monitoring.

However, pollution can also vary by a factor of 10 from one street to another. That’s why Plume Labs developed Flow, a smart air quality tracker that measures four main pollutants including PM2.5.

For Karl, the nearest monitoring station is in Tung Chung, on the other side of the mountain from where he lives in Discovery Bay. On the worst days pollution is visible, but health impacts can start long before smog appears.

“Sometimes we just don’t know!” he explains. “It’s why I’m looking forward to Flow, at the moment it can be really difficult to take decisions about pollution at the school.”

For more information about air quality in Hong Kong, download the Plume Air Report free on iOS or Android, or check our online forecasts. Want to go deeper? With Flow, now open for pre-orders in the US and Europe, you can know what you breathe wherever you are.

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