Abstract
The New Zealand region of Canterbury has experienced over three years of frequent seismic activity, centred under or near the main city of Christchurch. Larger earthquakes and aftershocks have triggered liquefaction in certain parts of the city, depositing significant amounts of fine silt on the surface, which is a new source of dust emissions. Historically, concerns about air quality in Christchurch have been dominated by emissions from wood burning in winter for domestic heating. High emissions, along with frequent temperature inversions lead to regular exceedances of the national standard for PM10 of 50 μg m-3 for a twenty-four hour average concentration. The health effects of PM10 are widely acknowledged, and regulatory drives to improve ambient air quality are succeeding in recent years. During 2011, ratios of PM2.5 to PM10 suggested that some periods of elevated concentrations were due to the liquefaction from the earthquakes and that the silt may represent a novel air quality issue to be managed. In addition, the earthquakes have damaged thousands of residences, causing changes in domestic heating practices as many chimneys are destroyed or currently in need of repair. This will affect emissions in upcoming winters and thus, the health burden may alter if a permanent step change in wood burning emissions is observed. However, the increased dust levels from liquefaction introduce a potentially compounding factor to any estimates of exposure. Thus, as a result of the earthquakes, air quality in Christchurch is rapidly changing with unknown effects on exposure and ultimately, the health of the Christchurch population.
Highlights
The city of Christchurch on New Zealand’s South Island has experienced over three years of regular seismic activity, beginning unexpectedly with an earthquake of magnitude 7.1 on September 4th 2010, just east of the city
The purpose of this letter is to inform about the initial air quality effects observed in Christchurch related to the continuing seismic activity, and to reflect upon the possible future changes in air quality due to the earthquakes
FUTURE AIR QUALITY IN CHRISTCHURCH. It is clear from the increased periods of elevated concentrations due to the coarser PM10 fraction, that a new source or sources of particulate matter have been introduced into the city of Christchurch
Summary
The city of Christchurch on New Zealand’s South Island has experienced over three years of regular seismic activity, beginning unexpectedly with an earthquake of magnitude 7.1 on September 4th 2010, just east of the city. A consequence of Christchurch’s sitting on an alluvial plain is that areas of the city, the eastern suburbs, are built on sandy soils that lose cohesion during earthquakes through a process called liquefaction. There is little documentation on the effects of earthquakes on air quality, there are interesting investigations into using changing levels of air pollutants as an indicator for imminent seismic activity in Greece [3] and Taiwan [4]. From the little published research, air quality effects from earthquakes are attributed to the dust generated by the destruction of buildings [5]. Other urban areas have experienced liquefaction during earthquakes, in Greece [6] and Turkey [7], and work has been published on the dangers liquefaction poses to buildings and industry, its potential contribution to local air quality is unknown. Estimating dust entrainment from any source is difficult, but so when the source is of an unknown size and broadly distributed
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