PM ₁₀ weekly periodicity in Beijing and Tianjin, 2000-2009: Anthropogenic or natural contributions?

This study investigates the weekly periodicity of PM ₁₀ (aerosol particulate matter with a diameter <10 μm) mass concentrations over Beijing and Tianjin as well as its relationship with synoptic-scale weather variability. The two cities are large air pollutant source regions that are often affected by the same weather system due to their close proximity. Comparison of the two cities, therefore, advances our understanding of the contributions of the weather variability (or anthropogenic emissions) to the weekly periodicity of PM ₁₀. Here we analyze PM ₁₀ anomalies against weekly means over the past 10 years (2000-2009) on the frequency domain using a fast Fourier transform. Results show that the interannual variabilities of PM ₁₀ weekly periodicity, defined as the ratio of 6-8-day variance to 2-14-day variance, between Beijing and Tianjin are correlated in the summer and fall, but are uncorrelated in the spring. In the fall, the higher correlation of PM ₁₀ weekly periodicity between the two cities may be associated with strong influence of the natural weather variability as represented by 850-hPa geopotential height, surface diurnal temperature range, and 1000-hPa wind. However, in the spring and summer, the influence of the weather variability on the PM ₁₀ weekly periodicity was not identified. The weather variability accounts for 0-85% of the PM ₁₀ weekly periodicity variation, with the maximal value in Beijing in the fall. These findings suggest that contribution of the weather variability to shaping the PM ₁₀ weekly periodicity over Beijing and Tianjin is restrictive and transient.