Sandstorm, or just an excuse?

First published: 24^th March 2010

If the source of the current air pollution is a sandstorm from northern China, can someone explain why the hourly figures recorded by the Environmental Protection Department (online) showed a gradual rise at the Central and Causeway Bay roadside stations, starting before midnight, in contrast to the low early morning levels and dramatic rise at 4am seen at the general stations and the Mong Kok roadside station? Are we choking on north China sands or our own vehicle exhausts, trapped by the current weather?

Also, why did so many stations miss readings on Monday, with no readings at all for midday?