[0] http://health.utah.gov/enviroepi/healthyhomes/epht/AirPollut...
Do they perform on the normal level after the pollution? That would be a hint that the results of the IQ tests just temporarily drop (I would be careful to say that the intelligence dropped).
If people leave the polluted area, they'll restore their normal intelligence. When I hear "reduction in intelligence", I immediately think that they talk about permanent reduction (because a big part of fluid intelligence is genetics, the efficiency of synapses and the amount of neurons - although some research [1] indicates that nurture and training can have significant effects on fluid intelligence).
It's unclear if they talk about permanent and irreversible damage IMO. For me it seems like they want to frame it that way which could be a bit clickbait-y depending on the matter of facts.
First, in general, air pollution inhibits respondents ’ test performance. Except for the effects of 1-d and 7-d air pollution exposure on math test scores (first and second columns in panel B), all of the coefficients for mean APIs over a longer period are negative and statistically significant.
Second, the damage of air pollution on cognitive performance is more sizable when using longer window of exposure measure. As shown at the bottom in panel A, an increase in the 7-d-mean API by 1 SD lowers verbal test scores by 0.278 point (0.026 SD), while a 1 SD increase in average API over 3 y before the interview is associated with 1.132 points (0.108 SD) drop in verbal test scores.
Third, air pollution exposure appears to exert a more negative effect on verbal test performance than math test performance.
That doesn't imply that the effect is irreversible, but it does mean that there are long-term changes which accumulate with longer exposure to air pollution.
Please correct me if I'm wrong. Sounds very interesting and I hope that people will finally fight against air pollution. Undoing it is not only healthier but also economically relevant. Sad that such studies seem to be necessary, but it's good that such revelations lead to more pressure for the policy makers.