EPA is developing an empirical model to relate ambient air quality to particulate emissions and land use in the surrounding area. This receptor-oriented model will be used for evaluating the effect of particulate control measures on concentrations at individual sites in a sampling network or for predicting air quality at a location where there is no sampler. Several studies have indicated that there is a statistically significant relationship between particulate concentrations measured at a high volume sampler and the emission density within a limited radius surrounding that site. It is EPA's intention to improve the correlation observed for this basic source/receptor relationship by accounting for some or all of the following factors in the empirical model: Distance to sources, direction of sources, differential impact of point and area source emissions, sampler and source heights, surrounding land use. By using weighting factors for different emissions in the area around the sampler, the model will build on the basic relationship and attempt to increase its accuracy.