Vertical Distribution Characteristics of PM2.5Observed by a Mobile Vehicle Lidar in Tianjin,China in 2016

We present mobile vehicle lidar observations in Tianjin, China during the spring, summer, and winter of 2016. Mo-bile observations were carried out along the city border road of Tianjin to obtain the vertical distribution characterist-ics of PM2.5. Hygroscopic growth was not considered since relative humidity was less than 60% during the observa-tion experiments. PM2.5profile was obtained with the linear regression equation between the particle extinction coef-ficient and PM2.5mass concentration. In spring, the vertical distribution of PM2.5exhibited a hierarchical structure. In addition to a layer of particles that gathered near the ground, a portion of particles floated at 0.6–2.5-km height. In summer and winter, the fine particles basically gathered below 1 km near the ground. In spring and summer, the con-centration of fine particles in the south was higher than that in the north because of the influence of south wind. In winter, the distribution of fine particles was opposite to that measured during spring and summer. High concentra-tions of PM2.5were observed in the rural areas of North Tianjin with a maximum of 350 μg m–3on 13 December 2016. It is shown that industrial and ship emissions in spring and summer and coal combustion in winter were the major sources of fine particles that polluted Tianjin. The results provide insights into the mechanisms of haze forma-tion and the effects of meteorological conditions during haze–fog pollution episodes in the Tianjin area.