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Figuring out the spot PSI
The haze is a major annoyance made worse by the fact that nobody tells you what the current Pollutant Standards Index (PSI) actually is. Sure, www.haze.gov.sg tells you the three-hour average and the 24-hour average, but what's the PSI, like right now?
Bad news: You can't figure out the spot PSI from the moving averages (feel free to figure out the math on a napkin over lunch).
Good news: But the official haze web site publishes the hourly concentrations of 2.5-micron particulate matter, which means we can figure out the spot PSI on our own.
Bad news: It's a pain in the asthma to have to do the calculations by yourself based on the formula.
Good news: I did it for you in a Google spreadsheet. (http://btd.sg/psisingapore if the link doesn't work). It grabs the latest 2.5-micron particulate matter concentrations from the official website, then calculates the spot PSI. The official three-hour average PSI is simply the mean of the latest three hourly spot PSI values.
Why don't the officials announce the spot PSI? First, there are hourly variations. Second, it's not just how much pollutants there are in the air right now, but also how long you've been exposed to them. The 24-hour and three-hour averages are therefore more helpful when it comes to deciding whether or not schools should be closed, for example.
All very fine and valid reasons. But the spot PSI reading satisfies a very natural curiousity about the actual state of matters. So it's time to set it free. Or as Lady Macbeth might say in very different circumstances, "Out, damned spot!"