Investigation of the association of black carbon and PM1 with planetary boundary layer in China

The frequently severe air pollution episodes in China have increasingly gained a concern and intensive studies. Planetary boundary layer height (PBLH) is a non-negligible factor dictating the vertical dilution of near-surface pollution. However, the relationship between boundary layer height (BLH) and fine particulate matter with an aerodynamic diameter less than or equal to 1μm (PM₁) and black carbon (BC) concentration across China, is still lacking sufficient research. In this study, by using L-band radiosonde measurements at 0800 and 2000 Beijing time (BJT), atmospheric composition stations and national meteorological stations in China during the period 2016 to 2017, the relationship of PBLH with PM₁ and BC are investigated. Both BC and PM₁ concentrations exhibits seasonal variability with the peak in winter, followed by fall, spring and summer, which is opposite to the seasonal variation of PBLH. This suggests a negative correlation between PBLH and surface aerosol concentration on seasonal timescale. In terms of diurnal timescale, PM₁ is also found to anti-correlate with PBLH at both 0800 and 2000 BJT with correlation coefficient (R) of −0.13 and −0.24, respectively. Albeit the relatively strong negative correlation (R=−0.2) of BLH-BC at 2000 BJT, the PBL is almost irrelevant with BC in early morning, which could be due to the fact that the PBL is not fully developed. Low BLHs, strong atmospheric stability, weak winds and high humidity in the lower troposphere collectively exacerbate the BC concentration in China, and such similar results are obtained when the analogical analysis is extended to PM₁.