Objectives for Office Buildings and Public Places in Hong
Kong (HKIAQO, HKEPD, 1999). The CO2 and NO2
peak concentrations from all the tested incense types
satisfy the criteria (1000 ppm, 79 ppb) set by HKIAQO.
However, the CO peak levels of seven incense types
significantly exceeded the HKIAQO standard. Especially
for Incense 3 and 10, the CO peak level exceeded 3
times more than the HKIAQO criteria, and exceeded the
US EPA’s National Ambient Air Quality Standards
(NAAQS, US EPA, 2000) for 1-h CO of 35 ppm.
Although Incense 2 and 6 were claimed to be environmental-
friendly, the quantity of the pollutants emitted
was not observed to be lower than the others. Both the
CO concentrations of incense 2 and 6 exceeded the
HKIAQO. Nevertheless, the NO and NOx emission
factors of incense 6 were the highest among all. It is
notable that the particulate matters from all the incense
significantly exceeded the requirement.