Long-term
ultrafine particle (UFP) exposure estimates at a fine
spatial scale are needed for epidemiological studies. Land use regression
(LUR) models were developed and evaluated for six European areas based
on repeated 30 min monitoring following standardized protocols. In
each area; Basel (Switzerland), Heraklion (Greece), Amsterdam, Maastricht,
and Utrecht (“The Netherlands”), Norwich (United Kingdom),
Sabadell (Spain), and Turin (Italy), 160–240 sites were monitored
to develop LUR models by supervised stepwise selection of GIS predictors.
For each area and all areas combined, 10 models were developed in
stratified random selections of 90% of sites. UFP prediction robustness
was evaluated with the intraclass correlation coefficient (ICC) at
31–50 external sites per area. Models from Basel and The Netherlands
were validated against repeated 24 h outdoor measurements. Structure
and model R2 of local models were similar
within, but varied between areas (e.g., 38–43% Turin; 25–31%
Sabadell). Robustness of predictions within areas was high (ICC 0.73–0.98).
External validation R2 was 53% in Basel
and 50% in The Netherlands. Combined area models were robust (ICC
0.93–1.00) and explained UFP variation almost equally well
as local models. In conclusion, robust UFP LUR models could be developed
on short-term monitoring, explaining around 50% of spatial variance
in longer-term measurements.