Network monitoring of speciated vs. total non-methane hydrocarbon measurements

Although total hydrocarbon (THC) instruments can provide instantaneous TNMHC mixing ratios (by subtracting methane) to approximate the levels of volatile organic compounds (VOCs), they lack speciated information, which is invaluable to establishing the link between the observation site and specific source influences. In contrast, PAMS observations with speciation information can be used to complement this deficiency. Examples of this complementarity were illustrated by comparing four common sites, with two mainly affected by urban/traffic emissions and two primarily affected by industrial emissions. The chemical composition of the air samples varied significantly between the four sites. Ethylene and propylene were found to be prominent at the two industrial sites, linking these samples strongly to the petrochemical industry nearby. This compositional signature was even more pronounced for the sample peak values. These findings suggest that network monitoring of TNMHCs may not be sufficient, and the lack of compositional information can be complemented by the more elaborate monitoring means such as PAMS deployed only at critical sites to provide both area coverage and speciation knowledge.