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Boundary layer height (BLH) is an important parameter in climatology and air pollution research, especially in urban city. We calculated the BLH with a bulk Richardson number (Ri) method over urban cities of China during 1980–2018 using European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-interim data after carefully validation with sounding data obtained from two meteorology stations in eastern China during 2010–2018. The values of BLH between these two types of data have correlation coefficients in the range of 0.65–0.87, which indicates that it is reasonable to analyze long-term trends of the BLH from ERA data sets. Using ERA-interim calculated BLH, we found that there is an increasing trend in the daytime BLH in most cities of eastern China, particularly during the spring season. A correlation analysis between the BLH and temperature, wind speed, relative humidity and visibility revealed that the variability in meteorological parameters, as well as in aerosol concentrations over highly polluted eastern China, play important roles in the development of the BLH.

The absorption and scattering of aerosols are critical factors that influence in global climate and visibility degradation. From January 2013 to December 2015, aerosol scattering coefficients, PM 2.5 , and meteorological parameters were continuously measured at a monitoring site in Shanghai, China. The annual means of scattering coefficients were 312.3, 232.1, and 261.9 Mm−1 for the years 2013, 2014, and 2015, respectively. The corresponding values for PM 2.5 were 61.6, 51.6, and 52.9 μg/m3. Compared with the average scattering coefficient of the year 2013, those of 2014 and 2015decreased by 26% and 16%, respectively. Furthermore, the annual average PM 2.5 decreased by 16% and 14% in 2014 and 2015, respectively. Although this study concluded that PM 2.5 was generally correlated with scattering coefficients during the entire measurement period, the decrease in the former was much less than the latter. On this basis, ultrafine particles may decrease significantly because they cause aerosol scattering. This finding should be investigated further in the future. The inter-annual meteorological changes affected PM 2.5 and scattering coefficient inter-annual variations. In the northwest and southwest direction, the seasonal and diurnal variations of aerosol scattering coefficients showed larger values when the wind speeds were about 3–5 m/s. The serious pollution in the northwest direction were mainly due to long-distance transport of pollutants during winter, whereas those in the southwest direction were attributed to local emission. The westerly wind frequency is the crucial factor influencing local pollution transport significantly. Backward trajectory analysis indicated that the air pollution in Shanghai in 2013–2015 is attributed to long-distance transport and primarily affected by the air mass from northwest direction. Observations on long-term aerosol optical properties on the basis of in-situ measurements can help thoroughly understand the radiative forcing characteristics of aerosol. • Aerosol σ sp in Shanghai reduced 26% and 16% in 2014 and 2015 compared to 2013. • PM 2.5 reduced by 16% and 14% in 2014 and 2015 compared to 2013. • Wind from NW direction causes long-distance transportation, from SW direction causes local transportation. • Locally dominated σ sp pollution in the spring and fall of 2013 and 2015. • Ultrafine particles may decrease significantly among the three years. [ABSTRACT FROM AUTHOR]