PM₁₀ Observed at a Meteorological Station in Beijing: Historical Trend and Implications

Inhalable particles (PM₁₀), with aerodynamic equivalent diameters that are generally 10 micrometers or smaller, are basic pollutants in many areas, especially in northern China, and thus the pollution from PM₁₀ inhalable particulate matter is a growing concern for public health. Independent long-term observations are necessary to evaluate the efficacy of PM₁₀ reduction actions. Variations in the PM₁₀ concentration from 2006 to 2017 at an observation station (NJ) in Beijing were recorded and analyzed. The average value ±1 standard deviation of daily mean PM₁₀ concentrations was 138.8 ±96.1 μg m^-3 for 1307 days (accounting for 34.7% of the total days), showing PM₁₀ concentration exceeding the National Ambient Air Quality Standard (NAAQS) 24-h average of 150 μg m^-3. Particulate concentration depended upon various meteorological conditions as also observed in this work: at low wind speed (< 4 m s^-1), the concentrations of PM₁₀ revealed a downward trend with -19 μg m^-3 per unit of wind speed, but when wind speed rose (> 4 m s^-1), the values increased by 49 μg m^-3 per unit of wind speed. In Beijing, air masses from northwest China, especially from the Gobi Desert and other desert areas, had net contributions to long-range transport of natural dust, enhancing the PM₁₀ concentrations by up to 29%. Overall, PM₁₀ mass concentration showed a significant downward trend with -8.0 μg/m³/yr from 2006 to 2017. Although with higher fluctuations in recorded data, similar downward trends derived from the government released data were also found at the nearby districts. The result delivered a proof of efficacy for the reduction actions recently adopted to limit PM₁₀ concentrations in Beijing. Very significant difference of diurnal changes in PM₁₀ concentrations was also found in two periods of 2006-2011 and 2012-2017, which might be due to the different contributions of fugitive dust. Nevertheless, further efforts, especially on controlling fugitive dust, should be planned as the PM₁₀ concentration annual mean value (94 μg m^-3) in 2017 still exceeded the NAAQS standard. The results showed that there is still a long way to go to reduce PM₁₀ in Beijing.