Dust Samplers

The effects of human exposure to air pollutants has been the subject of scientific research and government activity for several decades. Accumulating evidence demonstrates that exposure to air pollutants is associated with adverse health effects. Recently research has focussed on exposure in “micro environments” such as inside motor vehicles. Recent trends of population expansion, increased average vehicle kilometres travelled and increased vehicle ownership rates in cities such as Sydney, has resulted in over-congestion of surface roads. One response has been to build road tunnels. In December 2001, the M5 East freeway was opened to traffic and within six months in excess of 82,000 vehicles were using it daily. This freeway includes twin 4 kilometre tunnels (the longest in Australia), ventilated via a single exhaust stack. As it services major freight interchanges it carries a high proportion of trucks in comparison with other Sydney road tunnels. The combination of high usage (with higher truck numbers) and the ventilation characteristics of the tunnel mean that there is on occasion visible haze in the tunnels. In response to community concerns regarding in-tunnel pollution levels a study to monitor pollutant levels in vehicles was commissioned. The purpose of this study was to quantify exposure to several common motor vehicle pollutants during peak periods. They also wished to determine what impact vehicle ventilation had on pollutant levels. The study collected carbon monoxide (CO), carbon dioxide and fine particles over 94 trips and nitrogen dioxide (NO2), BTEX gases and fine particles over 372 trips, during a six week period. Transit times through the tunnels varied between 3-18 minutes.

Air monitoring was undertaken over 32 consecutive weekdays between 30 October and 12 December 2002. The monitoring equipment was installed in a well-maintained, government 2000 model Toyota Camry Station Wagon and operated by the same person throughout the study. The vehicle was driven by a second officer in the left-hand lane on all tunnel trips. Amongst other parameter such as NO₂ and CO, PM_2.5 was also measured.

PM_2.5 was measured using a real time dust monitor, separate measurements were taken in the eastbound tunnel during the morning peak period between 7-9 am; in the westbound tunnel in the afternoon peak period between 4-6 pm; and in the eastbound tunnel in the afternoon between 4-6 pm. The device was programmed to log every second and to calculate a trip average for PM_2.5.


PM_2.5 was  measured gravimetrically using an MicroVol 1100 low volume air sampler  fitted with a size selective inlet of 2.5 microns. Particulate was collected on a stretched Teflon filter that was changed every 5 days. Particles were collected over a 90-minute period per day during travels in both tunnels in the morning and afternoon peaks. Each single measurement was thus a weekly total covering all ventilation types.

The MicroVol measurement of PM_2.5 used gravimetric collection over all trips during a week. It thus reflects an average level of exposure for all ventilation scenarios. Comparing the two particle collection methods it would appear that the real time dust monitor overestimated PM_2.5 by around 80%. By comparison, a recent Sydney commuter study where exposures were measured for 5 hours in a car found a cabin PM_2.5 of 25μg/m³ using a Microvol. It was found levels nearly four times this averaged across all ventilation scenarios. Ambient PM_2.5 levels during the study period were 17μg/m³ or about 20% of the measured levels in the vehicle.


The study found that closing the car windows and switching the vehicle ventilation to recirculate can reduce exposures by approximately 70-75% for CO and NO₂, 80% for fine particles and 50% for BTEX gases. These benefits can be achieved whether or not the air conditioning system is in use.


The full study can be found at:

http://www.health.nsw.gov.au/pubs/2003/pdf/m5complete.pdf