... spatial clustering of air pollution and health data in the ACS study made it difficult to disentangle air pollution effects from those of spatial auto-correlation of health data per se. The ... the United States of America (National Morbidity, Mortality, and Air Pollution Study, NMMAPS) and Europe (Air Pollution and Health: a European Approach, APHEA) have produced effect estimates ... associations between air pollution and health; this, however, is not always so, suggesting that ambient PM measurements do not fully capture the toxic potential of complex ambient air pollution mixtures....