The Beijing−Tianjin−Hebei area, including Tianjin, incurs severe haze pollution. In this study, the mass concentrations of PM2.5 and gaseous pollutants for seven sites in Tianjin, together with pollutants in Beijing, ground meteorological factors, visibility, temperature, and humidity profiles, wind profiles, and backward trajectories during 20–28 February 2013, are used to analyze the pollution characteristics, meteorological causes, and boundary layer characteristics of heavy haze episodes. The average concentrations of PM2.5, SO2, NO2, CO, and O3 were 150, 87, 56, 2.4, and 22μg m–3, respectively. Although the variation of gaseous pollutants in different sites was large and significant, n only SO2 concentrations were in non-attainment, according to air quality grade limit of 50μg m–3. The PM2.5 variation over various sites in Tianjin showed regional and synchronous characteristics. PM2.5 concentrations during the research period far exceeded the grade limit value of 35μg m–3 and were 2–8 times higher, with a maximal hourly mean of 364μg m–3. High PM2.5 concentration is a key factor contributing to low visibility; the threshold PM2.5 mass concentration, corresponding to visibility <10 km, is 50μg m–3. PM2.5 concentration began to increase because of the local emission accumulating under weak winds and high humidity and rose steadily under sustained south winds; in additon, a fluctuating increase was found under weak north and east winds. The south and north winds then sheared quickly, and the peak value of PM2.5 reached the maximum because of the regional transport and repeated circulation and accumulation processes during the heavy pollution period. High PM2.5 concentration is associated with advection inversion, except when the advection inversion is caused by a prevailing strong east wind. During haze pollution episodes, high humidity occurred in the low and moderate layers of less than 500 m, and decreased quickly with height. The low-level jet between 200 m and 600 m curtailed the growth in PM2.5 concentration to some degree;in particular, the persistent, strong east wind contributed to a steady drop in PM2.5 to Grade II level. Pollution was removed effectively and quickly only when the entire layer was controlled by the strong northwest wind. Pollutants transported from Beijing and central and southwest area of Hebei province surrounding Tianjin made remarkable contributions to heavy pollution in Tianjin.%京津冀大气灰霾污染严重，天津市作为其核心组成之一其污染形势亦严峻。选取2013年2月20～28日天津重霾污染时段7站PM2.5（空气动力学当量直径小于等于2.5μm的颗粒物，即细颗粒物）和气态污染物数据，结合北京污染数据、地面气象要素、能见度、边界层温湿和风廓线、后向轨迹，深入分析重霾污染过程特征及气象和边界层成因。结果显示，研究时段天津 PM2.5、SO2、NO2、CO 和 O3浓度均值为150、87、56、2.4和22μg m−3,气态污染物各站差异显著，但仅有SO2全面超过国家空气质量一级标准（50μg m−3），而PM2.5具有区域同步变化特征，且严重超标，是一级标准（35μg m−3）的2～8倍，最高小时均值高达364μg m−3；高浓度PM2.5是导致低能见度的主因，能见度小于10 km对应PM2.5阈值为50μg m−3。弱风和高湿度导致局地排放累积，PM2.5始增，在高湿度条件下，持续偏南风促使其稳步增加，配合弱北风和弱东风PM2.5震荡上扬，污染高值阶段，南北气流短时迅速切换，区域污染传输叠加污染的循环累积，PM2.5浓度峰值达到最高；除因边界层强东风导致的平流逆温外，高浓度PM2.5与平流逆温密切相关；高污染时段高湿主要集中在500 m以下，且随高度递减幅度较大；位于200～600 m的低空急流一定程度抑制污染上升，尤其持续强东风使PM2.5浓度稳步降低到二级水平，污染迅速有效清除最终依赖整层的强西北风。北京、环绕天津的河北中部和西南部地区对天津重污染有显著贡献。
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