of borderline significanceP=0.092
Compared with the control community, the intervention community had a greater rate of decline in SO 2 concentration (0.051 μg/m 3 per year (95% confidence interval 0.019 to 0.083) P=0.003) and dust deposition (0.051 (0.019 to 0.083) kg/km 2 /month per year, P=0.003) during follow-up, and there was a difference of borderline significance between the two communities in the slope of concentration of NO 2 (0.033 (−0.013 to 0.079) μg/m 3 per year, P=0.092) and sulphation rate (0.020 (−0.001 to 0.041) μg SO 3 /100 cm 2 PbO 2 /day/year, P=0.059).