A study on the extent of global air pollution

I can't quite suss out the details, but it seems like they're saying that only 0.18% of global land area had levels of PM2.5 lower than the WHO's recommended levels _every day_.

Most of the study seems to be looking at how those levels vary by day, but the big claim doesn't reference % of days at all, which is odd. Their bullet points are a little confusing as well:

> Despite a slight decrease in high PM2.5 exposed days globally, by 2019 more than 70% of days still had PM2.5 concentrations higher than 15 μg/m³.

Where, though? They measured different geographic areas, but this has no geographic information. That leads me to believe that the claim is that on 70% of days there was at least one geographic location with PM2.5 concentrations higher than 15 μg/m³.

> In southern Asia and eastern Asia, more than 90% of days had daily PM2.5 concentrations higher than 15 μg/m³.

This is much clearer but suggests that my interpretation of the last bullet was wrong... maybe that one meant a global average?

I dunno, maybe I should read this again after some more coffee, but it seems to be written in a confusing way that goes back and forth from global averages to local averages to number of days above a threshold to annual averages.

* Any mask outside. Even surgical can cut more than half of pm 2.5

* A lot of people recommending indoor filters, but indoor pollution generally a lot less than outdoors except when cooking. You can verify this with a PM 2.5 monitor. I do recommend indoor filters, but if budget is limited and you're working on overall lower pm 2.5 filters, testing car and getting masks is the more effective intervention

Surgical mask source: https://smartairfilters.com/en/blog/surgical-masks-surprisin...

Best pm 2.5 monitor I found is a laseregg