[dahart]

It took me a few minutes to figure out how to read the Executive Summary (Table 0.1, page xvii).

The AQG number is the main recommendation, and refers to the concentration in micrograms per cubic meter (ug/m^3). So the report says the world should aim for 5 ug/m^3 or less of PM 2.5 annually, and 15 ug/m^3 or less PM 10 annually.

The interim targets are meant to be realistic goals to set along the way, so anywhere with worse than 75 ug/m^3 PM 2.5 on a daily basis might aim for that goal first.

I had to check how the concentrations compare to various AQI (Air Quality Index) reports, like my iPhone weather app. 5 ug/m^3 of PM 2.5 is an AQI of 21. Currently an AQI of 0-50 is considered “good”, so maybe down the road the scale will be adjusted based on these new recommendations.

https://www.airnow.gov/aqi/aqi-calculator-concentration/

Curious to see what the previous recommendations were, the 2005 report has the same first 3 interim targets for PM 2.5 and PM 10. The current report’s 4th interim target is set to the AQG (final recommendation) level from the previous report, and the new AQG level is now lower than the previous one. This is because there is now stronger statistical evidence of health damage occurring at levels above the new recommendation, the data has shown we needed a new lower threshold.

[strogonoff]

> So the report says the world should aim for 5 ug/m^3 or less of PM 2.5 annually, and 15 ug/m^3 or less PM 10 annually.

Looks like a decent guideline, but it’s important to keep in mind that there appears[0] to be no safe level of particulates.

[0] https://en.wikipedia.org/wiki/Particulates

[infogulch]

I wonder if there's a difference in harm caused between human-generated particulates vs particulates from, say, a forest. I assume at some point as air quality improves, natural pollen, bacteria, etc, would become a significant factor in simplified PM-based AQI, and my question is, is that still a problem?

[rubatuga]

Something like aerosolized salt from a humidifier using tap water is essentially harmless. But it still counts as PM2.5

[MichaelZuo]

Certain types of fine particulates are certainly more harmful than even forest fire smoke. For example asbestos, brake dust, leaded gasoline in dust, etc.

But the vast majority would probably be roughly the same.

[gruez]

>So the report says the world should aim for 5 ug/m^3 or less of PM 2.5 annually, and 15 ug/m^3 or less PM 10 annually.

what does "annually" mean in this context? That your time-weighted expousure should be less than 5 ug/m^3, or that it should be always under 5 ug/m^3?

[dahart]

The former; it means the average exposure over the year. The latter “always under” guideline is also included as a separate item: they recommend that your 99th percentile maximum daily exposure stay less than 15 ug/m^3 for PM 2.5, and less than 45 ug/m^3 for PM 10. 99th percentile means they recommend this level 99% of the time, and assume/allow for several days per year of exposure to higher concentrations.

There are recommendations for other specific pollutants too, I left those out, but the table includes recommendations for O3, NO2, SO2, and CO. There’s a 2nd table on the next page with recommended maximum exposures for those last 3 in terms of 1-hour and other timeframes smaller than 24 hours.