Ambient air quality standards have averaging times of ranging, from one hour for carbon monoxide and ozone to one year for sulfur dioxide and nitrogen oxide. However, commercial manufacturers and distributors of air pollution monitoring equipment aim to sell expensive real-time monitoring equipment, linked to the Internet where people could see the trends of air quality. While the instantaneous presentations of the results could mesmerize the public and decision-makers unfamiliar with technical issues on air quality monitoring, the prohibitive cost of such system (US$300,000 to 700,000 per monitoring site) makes the usefulness of the monitoring data of little value to actual policy making. Also, the monitoring stations are limited in number and often sparsely located. The operating and maintenance cost of the monitoring stations is very expensive, ranging from $20,000 to 50,000 annually. Real time air quality monitors then often serve as promotional display, often located in the middle of parks and places of thick vegetation, negating its main and actual purpose.
However, with budget constraints, far more cost-effective options are available. In the last 20 years, passive samplers have been developed and used satisfactorily. Compared with real time monitors, passive samplers are cheap, costing from $5 to 10 per sample. Instead of one sample for one urban area, the air quality could be monitored at a hundred sites at a fraction of the annual and operating cost of an open path sampler. One drawback of passive samplers though is the frequent need to take, remove, and change the sampler depending on the averaging time of the pollutant.
Passive samplers were shown to be very effective. The World Bank and Asian Development Bank used the passive sampler in monitoring the sulfur dioxide concentration in its RAINS-ASIA program. The monitoring results were used to calibrate a complex acid rain regional model and development regional strategies. In the past, the cost of passive samplers and analysis was much higher, by as much as a factor of three as the equipment for analyzing the samples were in the early stages of development and very few laboratories in the world have the capability. The samplers were sent to Europe for analysis. Today the equipment for analysis could be purchased at around $50,000.