Going back to the beginning:
Is that by weight or by volume? It doesn't matter too much when we're talking about liquids that have a similar density, but here I think it might. Let's assume it's by weight...
Math so far seems reasonable. Call it 3500 liters of air, just as a round number. That would be 3.5 cubic meters. At standard temperature and pressure, that would be ~4.5 kilograms of air. One part per thousand would be 4.5 grams. One part per million would be 4.5 milligrams. Multiply by 0.02 and we get 0.09 milligrams or 90 µg exposure per day.
Now we have something we can compare to the ppm (aka µg/ml) values we see in e-liquid test results. If you vape say, 5ml a day of a liquid with 500 µg/ml, your daily exposure is 2500 µg.
Still think it's overblown?
Your calculations are way way off, example
NIOSH submits letter to the editor concerning our diacetyl study
"Based on mild and moderate activity, the NIOSH-estimated safety exposure limit would be 86micrograms/day (mild activity) and 302micrograms/day (moderate activity) for diacetyl, and 132micrograms/day (mild activity) and 638micrograms/day (moderate activity) for acetyl propionyl. Our initial calculations considering resting ventilation rate was 65micrograms/day for diacetyl and 137micrograms/day for acetyl propionyl. Thus, the NIOSH-set limits are approximately 50-400% higher than what we considered in our original study, using the worst case scenario."
My calculations fall directly in line with Dr. F's and niosh numbers.
The safety limit number they used for da was .05ppb.
If you convert ppb to ppm its .00005ppm present in the air per each ml of air taken in.
Now, multiply that .00005 by the amount of ml of air taken in a day, what does it give you?
168-192ppm per day, or in other words falls directly in the middle of their numbers.
What are their numbers? 86 - 302ppm per day.
The NIOSH safety limit in the air was .05ppb, vs. the .02ppm number I used that was one of the lower values measured in office settings.
