Table 4.

Multivariate mixed effects regression models of outdoor residential UFP concentration^†

	Model 1 No fixed sites		Model 2 SPH site		Model 3 MAC site		Model 4 SPH and MAC sites
Covariate	% change	95% CI	% change	95% CI	% change	95% CI	% change	95% CI
log(UFPsPH)*	-	-	3	2, 3	-	-	0.4	0.1, 0.8
log(UFPMAC)*	-	-	-	-	6	6, 7	6	6, 7
Distance to highway
>1000 m (ref)	-	-	-	-	-	-	-	-
100-400 m	21	5, 55	37	3, 82	32	-6, 83	34	-0.7, 81
< 100 m	56	18, 105	78	29, 147	73	19, 53	77	25, 149
Wind speed (m/s)	−18	−20, −17	−16	−18, −15	−6	−7, −4	−6	−7, −4
Wind direction
Southeast (ref)	-	-	-	-	-	-	-	-
West	−35	−39, −31	−27	−31, −22	7	0.8, 14	8	1, 14
Northwest	−47	−50, −43	−42	−45, −38	−6	−12, −0.4	−6	−12, −0.4
East	−47	−50, −44	−45	−48, −41	−27	−31, −23	−27	−31, −23
Traffic volume (veh/hour)
<5340 (ref)	-	-	-	-	-	-	-	-
5340–8630	43	35, 51	32	24, 39	13	8, 19	12	7, 18
> 8630	33	24, 43	23	14, 32	7	0.3, 14	6	−0.5, 13
Precipitation (yes/no)	−12	−17, −7	−8	−13, −3	−9	−13, −4	−8	−12, −4
Hour (sine)	−21	−23, −18	−19	−21, −17	−14	−16, −12	−14	−16, −12
Hour (cosine)	−19	−23, −16	−14	−18, −11	−8	−12, −5	−8	−11, −4
AIC	4912		4743		3883		3886

Abbreviations: UFP, ultrafine particles; log(UFP_SPH), log(UFP) at the Harvard School of Public Health monitoring site; log(UFP_MAC), log(UFP) at the Mystic Activity Center monitoring site; AIC, Akaike Information Criterion; ref, reference category.

^*Represents the percent increase in residential outdoor UFP for a 10% increase in fixed site UFP.

^†Includes data from 16 homes and 3,297 hour measurements.