Fig. 3. Time series of PM2.5 daily concentration, hourly ambient temperature, relative humidity, wind speed/direction, visibility and 3-hourly mixing layer height (computed from
the NCEP Global Data Assimilation System (GDAS) model, http://ready.arl.noaa.gov/READYamet.php) in (a) Shanghai, (b) Beijing, and (c) the Huaniao Isle during Jan. 1e19 (the
missing PM2.5 data is due to raining or the maintenance of samplers).