Meteorological Change and Impacts on Air Pollution: Results From North China

There have been speculations that the severe air pollution experienced in North China was the act of meteorological change in general and a decreasing northerly wind in particular. We conduct a retrospective analysis on 1979-2016 reanalysis data from ERA-Interim of European Centre for Medium-Range Weather Forecasts over a region in North China to detect meteorological changes over the 38 years. No significant reduction in the northerly wind within the mixing layer is detected. Statistically significant increases are detected in the surface temperature, boundary layer height and dissipation, and significant decreases in relative humidity in the region between the first and second 19-year periods from 1979 to 2016. We build regression models of PM(2.5)on the meteorological variables using data in 2014, 2015, and 2016 to quantify effects of the meteorological changes between the two 19-year periods on PM(2.5)under the emission scenarios of 2014-2016. It is found that despite the warming, dew point temperature had been largely kept under control as the region had gotten dryer. This made the effects of temperature warming largely favorable to PM(2.5)reduction as it enhances boundary layer height and dissipation. It is found that the meteorological changes would lead to 1.29% to 2.76% reduction in annual PM(2.5)averages with January, March, and December having more than 4% reduction in the 3 years. Thus, the meteorological change in North China had helped alleviate PM(2.5)to certain extent and should not be held responsible for the regional air pollution problem.