You have shared two sources of broad, country-level data.

The study tracked localized effects on individuals.

These are not necessarily in contradiction! Though whatever you're inferring with your broad correlation (air pollution has no negative effect on intelligence? air pollution improves intelligence?) is much weaker than the study, which clearly has made attempts to isolate variables.

Have you considered that the educational level in the developing world has increased dramatically from a low base, while pollution had so far been manageable in most cities until the most recent couple of decades?

When one increased the average education level by something like 5-10 years, as was the case in many Asian countries in the last century, it is not surprising there was a significant increase in intelligence. Thankfully the effect of pollution has not been drastic enough to negate all of those gains. It still does not mean we should neglect its likely significant negative impact.

From the paper:

> Cutting annual mean concentration of particulate matter smaller than 10 μm (PM10) in China to the Environmental Protection Agency’s standard (50 μg/m3) would move people from the median to the 63rd percentile (verbal test scores) and the 58th percentile (math test scores), respectively.

Really, your criticism of a study looking at those two factors in local detail and trying to correct for correlation with outside factors is "but globally they correlate"? (and also correlate with everything that's on a long-term upwards trend when nations are developing/industrializing)

Perhaps IQs would have increased more without pollution?

Sure. The objective data I provided shows a correlation and not a causation. But it contradicts the study of a "huge" reduction in intelligence due to air pollution.

If air pollution causes reduction in intelligence, IQs would not have increased so much in the past 100 years as air pollution skyrocketed.

Can't say air pollution causes huge reduction in intelligence while IQs have drastically increased in an increasing air pollution environment.

The study claims a causal relationship - air pollution causes huge reduction in intelligence. The objective data of the last 100 years clearly shows that's not true.

Over the last two centuries, you would expect to find a direct causal link between industrialization and intelligence, as governments have introduced mass education for the first time, to create a skilled labour force.

Because industrialization is also positively correlated with pollution and urbanization, especially during its first phase, you would also expect to find a long-term positive correlation between pollution and intelligence.

However, if you factor out the positive effects of mass education, then you will likely find, as expected, that intelligence decreases as toxicity of the environment rises.