Abstract. The Chinese government has made many efforts to mitigate fine particulate
matter pollution in recent years by taking strict measures on air pollutant reduction, which has generated the nationwide improvements in air quality
since 2013. However, under the stringent air pollution controls, how the
wintertime PM2.5 concentration (i.e., the mass concentration of
atmospheric particles with diameters less than 2.5 µm) varies and how
much the meteorological conditions contribute to the interannual variations
in PM2.5 concentrations are still unclear, and these very important for
the local government to assess the emission reduction of the previous year and
adjust mitigation strategies for the next year. The effects of atmospheric
circulation on the interannual variation in wintertime PM2.5
concentrations over the Beijing–Tianjin–Hebei (BTH) region in the period of
2013–2018 are evaluated in this study. Generally, the transport of clean and
dry air masses and an unstable boundary layer in combination with the effective
near-surface horizontal divergence or pumping action at the top of the
boundary layer benefits the horizontal or vertical diffusion of surface
air pollutants. Instead, the co-occurrence of a stable boundary layer,
frequent air stagnation, positive water vapor advection and deep
near-surface horizontal convergence exacerbate the wintertime air pollution.
Favorable circulation conditions lasting for 2–4 d are
beneficial for the diffusion of air pollutants, and 3–7 d
of unfavorable circulation events exacerbates the accumulation of air
pollutants. The occurrence frequency of favorable circulation events is
consistent with the interannual variation in seasonal mean PM2.5
concentrations. There is better diffusion ability in the winters of 2014 and
2017 than in other years. A 59.9 % observed decrease in PM2.5
concentrations in 2017 over the BTH region could be attributed to the
improvement in atmospheric diffusion conditions. It is essential to exclude
the contribution of meteorological conditions to the variation in
interannual air pollutants when making a quantitative evaluation of emission
reduction measurements.
Corrigendum to "Effects of climate variability and functional changes on the interannual variation of the carbon balance in a temperate deciduous forest" published in Biogeosciences, 9, 13–28, 2012
