Short CommunicationSevere haze episodes and seriously polluted fog water in Ji'nan, China

•Spatial distributions of PM2.5 over China during server haze episodes were given.•Fog water was seriously polluted due to longtime and large-scale haze pollution.•Fog events reduced ambient air pollutants but difficult to cleanse the air.

Haze episodes often hit urban cities in China recently. Here, we present several continuous haze episodes with extremely high PM2.5 levels that occurred over several weeks in early 2013 and extended across most parts of the northern and eastern China-far exceeding the Beijing-Tianjin-Hebei region. Particularly, the haze episode covered ~ 1 million km2 on January 14, 2013 and the daily averaged PM2.5 concentration exceeded 360 μg m− 3 in Ji'nan. The observed maximum hourly PM2.5 concentration in urban Ji'nan reached 701 μg m− 3 at 7:00 am (local time) in January 30. During these haze episodes, several fog events happened and the concurrent fog water was found to be seriously polluted. For the fog water collected in Ji'nan from 10:00 pm in January 14 to 11:00 am in January 15, sulfate, nitrate, and ammonium were the major ions with concentrations of 1.54 × 106, 8.98 × 105, and 1.75 × 106 μeq L− 1, respectively, leading to a low in-situ pH of 3.30. The sulfate content in the fog sample was more than 544 times as high as those observed in other areas. With examination of the simultaneously observed data on PM2.5 and its chemical composition, the fog played a role in scavenging and removing fine particles from the atmosphere during haze episodes and thus was seriously contaminated. However, the effect was not sufficient to obviously cleanse air pollution and block haze episodes.