PM10 concentrations and mass transport during “Red Dawn” – Sydney 23 September 2009

The dust storm on 22 and 23 September 2009, called “Red Dawn”, was the largest to pass over Sydney in term of reduced visibility (400 m) since reliable records began in 1940. The maximum hourly PM10 concentration measured near Sydney was 15,366 μg/m3 at Bringelly and is the highest ever recorded for Sydney and possibly any Australian capital city. The Australian air quality standard of 50 μg/m3 per 24 h was massively exceeded at Randwick (1734 μg/m3) and Newcastle (2426 μg/m3). Red Dawn was caused by drought and the extreme wind conditions caused by a low pressure trough and cold front associated with a deep cut-off low pressure system. The source of the dust was the red sandplains of western New South Wales, the sandplains, riverine channels and lakes of the lower Lake Eyre Basin and Channel Country of Queensland. Between 22 September 2009 at 1400 and 23 September 2009, 0.3 Mt of PM10 dust was transported off the coast between Albion Park and Newcastle (182 km length) near Sydney. The maximum hourly rate of PM10 dust lost off the coast near Sydney was 71,015 t/h on 22 September at 2100. Calculating the total suspended particulate sediment lost off the Australian coast for the 3000 km long Red Dawn dust storm gives an estimate of 2.54 Mt for a plume height of 2500 m. This is the first and largest off-continent loss of soil ever reported using measured, as apposed to modelled, dust concentrations for Australia.

► We report on “Red Dawn” the largest dust storm to hit Sydney since records began in 1940.
► Red Dawn was caused by extreme drought and gale force winds.
► Hourly PM10 dust concentrations peaked at 15,366 μg/m3 at 2000 on 22 September UTC.
► 2.54 Mt of dust blew off the coast over a 24 h period.