Using multiple continuous fine particle monitors to characterize tobacco, incense, candle, cooking, wood burning, and vehicular sources in indoor, outdoor, and in-transit settings

This study employed two continuous particle monitors operating on different measurement principles to measure concentrations simultaneously from common combustion sources in indoor, outdoor, and in-transit settings. The pair of instruments use (a) photo-charging (PC) operating on the principle ionization of fine particles that responds to surface particulate polycyclic aromatic hydrocarbons (PPAHs), and (b) diffusion charging (DC) calibrated to measure the active surface area of fine particles. The sources studied included: (1) secondhand smoke (cigarettes, cigars, and pipes), (2) incense (stick and cone), (3) candles used as food warmers, (4) cooking (toasting bread and frying meat), (5) fireplaces and ambient wood smoke, and (6) in-vehicle exposures traveling on California arterials and interstate highways. The ratio of the PC to the DC readings, or the PC/DC ratio, was found to be different for major categories of sources. Cooking, burning toast, and using a “canned heat” food warmer gave PC/DC ratios close to zero. Controlled experiments with 10 cigarettes averaged 0.15 ng mm−2 (ranging from 0.11 to 0.19 ng mm−2), which was similar to the PC/DC ratio for a cigar, although a pipe was slightly lower (0.09 ng mm−2). Large incense sticks had PC/DC ratios similar to those of cigarettes and cigars. The PC/DC ratios for ambient wood smoke averaged 0.29 ng mm−2 on 6 dates, or about twice those of cigarettes and cigars, reflecting a higher ratio of PAH to active surface area. The smoke from two artificial logs in a residential fireplace had a PC/DC ratio of 0.33–0.35 ng mm−2. The emissions from candles were found to vary, depending on how the candles were burned. If the candle flickered and generated soot, a higher PC/DC ratio resulted than if the candle burned uniformly in still air. Inserting piece of metal into the candle's flame caused high PPAH emissions with a record PC/DC reading of 1.8 ng mm−2. In-vehicle exposures measured on 43- and 50-min drives on a California arterial highway gave PC/DC ratios of 0.42 and 0.58 ng mm−2, with one-min average PC/DC ratios varying along the roadway due to the different types of vehicles. Interstate highways had PC/DC ratios of approximately 0.5 ng mm−2 with ratios above 1 ng mm−2 when driving behind diesel trucks. These PC/DC ratios were higher than the “signature” value of the cigarette (0.11–0.19 ng mm−2) measured in a large Indian gaming casino with smoking. Simultaneous continuous monitors operating together can provide useful information to help differentiate source categories. The PC/DC ratio reflects the mass of PAHs per unit of active surface area of the particles, and therefore we expect it to be relevant to the toxicity of fine particles.