Multi-day pollution episodes involving all types of air pollutants
usually occur in Hanoi following the northeast monsoon surges in
winter that bring in continental cold air from the Asiatic highpressure
anticyclone. This study provides insights into the atmospheric
processes underlying the occurrence and evolution of WPEs
using continuous monitoring data on air pollutants and surface meteorology
as well as information on upper-air soundings and air mass
trajectories. Although the analysis was based on monitoring data for
the winter of October 2003 to February 2004, atmospheric conditions
controlling the daily and diurnal variations in pollutant concentrations
during WPEs found in this study occur almost similarly in
other winters.