Comparison of particle lung doses from the fine and coarse fractions of urban PM-10 aerosols

The U.S. Environmental Protection Agency (EPA) recently revised the nationa l ambient air quality standards to include a new PM-2.5 particulate standar d. We examine the contributions of fine (PM-2.5) and coarse (PM-2.5 to -10) fraction of typical urban aerosols to particle doses in different lung air ways resulting from 24-h exposure to the standard concentration of 150 mu g m(-3). The aerosol is assumed to have a bimodal lognormal mass distributio n with mass median diameters of 0.2 and 5 mu m, and geometric standard devi ation of 1.7 and 57% of the mass in the fine (PM-2.5) mode. The daily mass dose from exposure to 150 mu g m(-3) of PM-10 in the nasopharyngeal (NPL) r egion is 20-51 mu g day(-1) (7.5% of inhaled fines) and 377-687 mu g day(-1 ) (30% of inhaled coarse), respectively, of fine and coarse mass filtered i n the nose. Similar daily mass doses from fine and coarse fractions, respec tively, to the tracheobronchial (TBL) region are 28-38 (1.5%) and 40-52 (4% ) mu g day(-1) and to the pulmonary (PUL) region are 18-194 (6%) and 32-55 mu g day(-1) (2%). The daily number dose in the NPL region is 5-15 x 10(8) (0.06% of inhaled fines) and 5-10 x 10(6) day(-1) (13% of inhaled coarse) r espectively, of fine and coarse particles. Similar number doses to the TBL region are 2.2-3.1 x 10(10) (2%) and 7.1-11.1 x 10(5) (2%) day(-1) and to t he PUL region are 1.6-16.7 x 10(10) (9%) and 2.9-17.0 x 10(5) (3%) day(-1). The daily surface mass dose (mu g cm(-2) day(-1)) from coarse fraction par ticles is large in generations 3-5. The daily number dose (particles day(-1 )) and surface number dose (particles cm(-2) day(-1)) are higher from the f ine than the coarse fraction, by about 10(3) to 10(5) times in all lung air ways. Fine fraction particles result in 10,000 times greater particle numbe r dose per macrophage than coarse fraction particles. Particle number doses do not follow trends in mass doses, are much larger from fine than coarse fraction, and must be considered in assessing PM health effects. For the as sumed fine fraction ratio of 0.57, the estimated increase in protection fro m the new PM-2.5 standards is a 25% and 47% lower dose, respectively, at th e 24-h and annual standard in comparison with the respective PM-10 standard s. The mass fraction in the fine mode depends upon the local sources, will vary with different extents of control of various source types, and will in fluence the choice of control strategy to meet the revised standard.