Speciation and atmospheric abundance of organic compounds in PM2.5 from the New York City area. I. Sampling network, sampler evaluation, molecular level blank evaluation

This study demonstrates an approach for evaluating a molecular level sampling and analysis protocol for organic marker compounds at the high picogram m-3 (ppt) to low nanogram m-3 (ppb) mass concentrations in urban and background receptor sites. The Speciation of Organics for Apportionment of PM2.5 in the New York City Area (SOAP) project was conducted from May 2002 to May 2003 at four sites in New York City, New Jersey, and Connecticut. Its chief objectives were to expand the chemical characterization of organic compounds and to estimate the source contributions of carbonaceous fine particles at urban and background monitoring sites. Two major challenges were faced in order to successfully implement the SOAP sampling network. First, collection of adequate fine PM mass was necessary for successful quantitation of organic marker compounds. Second, sufficiently low blank levels were required for each marker compound for accurate identification and quantitation needed for source-receptor modeling. Initial field tests of representative samplers designed for sampling PM chemical species indicated insufficient sample mass collection, unless analytical sensitivity for organic markers could be greatly improved. Adequate PM mass was collected using a Tisch TE-1202 sampler that operated at a much higher flow rate (113 lpm). Preliminary field tests also revealed unacceptably high travel blank levels for n-alkanes and carboxylic acids. The mass of organic marker compounds observed on travel blank filters was reduced significantly by shipping filters in sealed filter holders. Further evaluation of the Tisch TE-1202 sampler also demonstrated the sampler was free of organic components and impactor grease upstream of the filter. These features also reduced the contribution of carbonaceous species to system blanks and therefore, to the total mass collected. As a result, blank levels for hopanes, PAHs, and dicarboxylic acids were below limits of detection (LOD), and n-alkanes (C25 to C32), n-alkanoic acids (C12, C14, C16, and C18), and phthalic acid exhibited acceptable low levels in all SOAP blanks ranging from 1 to 10 times the limit of detection for each compound class. Overall, adequate sample mass and sufficiently low blank levels were achieved successfully with the SOAP fine particle collection protocol.