Table 6.

Results of independent external validation using air pollution data from the routine monitoring sites

Pollutant	N	Mean overprediction (standard deviation)	R 2
NO2 (μg/m3)a	102	−2.2 (5.8)	0.75
PM2.5 (μg/m3)	10	0.090 (1.5)	0.83
PM2.5 absorbance (10−5 m−1)b,c	5	−0.13 (0.28)	0.52
PM10 (μg/m3)	82	0.77 (4.9)	0.71
PMcoarse (μg/m3)	10	1.2 (1.7)	0.65
PNC (particles/cm3)c	4	−5058 (17678)	0.00

^aNO₂ LUR models were applied to 102 sites in total: the area-specific NO₂ models were applied to 26 routine monitoring sites within 10 km of the SAPALDIA measurement areas, alpine NO₂ models were applied to 4 routine monitoring sites outside of SAPALDIA measurement areas, with altitudes above 1000 m, and non-alpine NO₂ models were applied to 72 routine monitoring sites outside of the SAPALDIA measurement areas, with altitudes below 1000 m (Fig. 1); ^bThe routine monitoring sites measured elemental carbon or soot, but this is known to correlate highly with PM_2.5 absorbance; ^c The PM_2.5 absorbance and PNC models included area indicators, and were only applied to the sites within 20 km of the SAPALDIA measurement areas