If you have been hearing about poor air quality in New York City Friday, you can breathe a deep sigh of relief (literally): our air quality is fine. Typical air quality in the city falls below 50 on the air quality index (AQI), within the “good” range.
The past few days have seen air quality tick over into the 60s, edging us into the “moderate” category on the AQI. But just barely. Within this range, air quality is nowhere near a level that would begin to cause any distress to people walking or exercising outside, even if you belong to a more sensitive group.

Our slightly higher number on the AQI is a result of marginally higher concentrations of particulate matter (PM 2.5) in the air. You’ll often see us talking about PM 2.5 when wildfire smoke is filtering into our region; thankfully that is not the case this time around.
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Instead, these particulates are coming from standard city activity: car exhaust, industrial emissions, anything involving the burning of fossil fuels.

So if this is just standard city pollution, why is the AQI higher than it usually is?
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We actually have our quiet weather to thank. High pressure has been dominating over our region most of the week. This has kept our weather dry and sunny, but it also means our air hasn’t been moving much. While you often associate high pressure with “good” weather, that “good” weather comes thanks to sinking air. But this sinking air acts like a lid over the air at the surface holding it, and the pollutants within it, in place.
Simply put: high pressure makes it harder for polluted air to rise and disperse, turning air at the surface stale, especially the longer high pressure stays around. An extreme example of this is the Great Smog of London in 1952, but we are nowhere near anything like that.

You are free to go about your day unencumbered by the air quality; it’s not a difference even perceptible to most people. But if you want to look to the horizon, you can catch a glimpse of the layer of stale air trapped at the surface, as seen in the shot below from Earth Cam’s Statue of Liberty camera.
