Composition and Integrity of PAHs, Nitro-PAHs, Hopanes, and Steranes in Diesel Exhaust Particulate Matter

Diesel exhaust particulate matter contains many semivolatile organic compounds (SVOCs) of environmental and health significance. This study investigates the composition, emission rates, and measurement integrity of 25 SVOCs, including polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs (NPAHs), and diesel biomarkers hopanes and steranes. Diesel engine particulate matter (PM), generated using an engine test bench, three engine conditions, and ultralow sulfur diesel (ULSD), was collected on borosilicate glass fiber filters. Under high engine load, the PM emission rate was 0.102 g/kWh, and emission rates of Sigma PAHs (10 compounds), Sigma NPAHs (6 compounds), Shopanes (2 compounds), and Sigma steranes (2 compounds) were 2.52, 0.351, 0.02-2 and 1 mu g/kWh, respectively. Storage losses were evaluated for three cases: conditioning filters in clean air at 25 degrees C and 33 % relative humidity (RH) for 24 h, storing filter samples (without extraction) wrapped in aluminum foil at 4 degrees C for up to 1 month, and storing filter extracts in glass vials capped with Teflon crimp seals at 4 degrees C for up to 6 months. After conditioning filters for 24 h, 30 % of the more volatile PAHs were lost, but lower volatility NPAHs, hopanes and steranes showed negligible changes. Storing wrapped filters and extracts at 4 degrees C for up to 1 month did not lead to significant losses, but storing extracts for 5 months led to significant losses of PAHs and NPAHs; hopanes and steranes demonstrated greater integrity. These results suggest that even relatively brief filter conditioning periods, needed for gravimetric measurements of PM mass, and extended storage of filter extracts, can lead to underestimates of SVOC concentrations. Thus, SVOC sampling and analysis protocols should utilize stringent criteria and performance checks to identify and limit possible biases occurring during filter and extract processing.