Ambient aerosol exposure-response as a function of particulate surface area: Reinterpretation of historical data using numerical modelling

It has been hypothesized that the curvilinear response between British Smoke (BS) and excess mortality in London between 1958 and 1972 may be attributable to a linear response with respect to particulate number or surface area concentration. A numerical model has been developed and used to derive relationships between aerosol number, surface area and mass concentration under idealized environmental conditions. Modelling demonstrates that for a constant aerosol generation rate and rapid mixing, generalized functions can be derived that describe particle number versus mass concentration, and surface area versus mass concentration. The results indicate that the epidemiology data do not support a linear association between particle number concentration and mortality rate. However, a transformation between BS and particulate surface area is presented that leads to a linear association between aerosol surface area concentration and mortality rate. A critical mass concentration is defined, below which aerosol surface area varies linearly with mass. Above the critical mass concentration, numerical modelling supports the hypothesis that aerosol surface area is a more appropriate indicator of health effects associated with exposure.