Survey of residential indoor particulate matter measurements 1990-2019.

The pooled regression for Western Europe (excluding Spain and Finland, whose residuals variances were too different from the rest) shows a highly significant decreasing trend of −0.94 ± 0.14 μg/m 3 per year ( p -value of coefficient: 3E–10).

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While PM 2.5 concentrations show statistically significant decreasing patterns for China, Taiwan, Beijing, and marginally significant for Taipei, no trends are significant for other individual East Asian cities, or for Japan, which can reflect a real lack of trend, lack of data, or both.

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