6. discussion
the data from north kensington, halifax and edinburgh provide good evidence that relationship presented in the 2007 paper has more general application, within a range of some 25%, without further numerical parameters being applied. this is demonstrated by good linear fits. with small zero intercepts. being obtained , with values of .. / within 25% of unity. variation at this scale is expected purely because of measurement uncertainties such as those from air leaks around the seal with the filter. with more accurate instrumentation, the value of ...2 would also be expected to vary,