problems associated with estimation of human exposure to ambient air pollutants are discussed . 
 ideally , we would prefer to have some indication of actual dose . for most pollutants 
 this is not presently feasible . 
 specific problems discussed are adequacy of outdoor monitors ; the need to correct for exposures and time spent indoors ; the need to have particle size distributions described and the chemistry of the particles presented . 
 these indicate the need to develop lightweight accurate and reliable personal monitors.imagesfigure 1 .