Trace element mass fractions in road dust as a function of distance from road

Figures & data

Figure 1. Distribution of sampling sites within the greater Boston metropolitan area

Back represents samples taken at a distance > 300 m; Near-road represents samples taken at a distance range of 26 to 200 m; Road represents samples taken at a distance range of 0 to 25 m.

Figure 2. Mass fractions of Ba, Ca, Cu, Fe, Zn and Zr at different distance ranges

SD represents the standard deviation: Back represents samples taken at a distance > 300 m; Near-road represents samples taken at a distance range of 26 to 200 m; Road represents samples taken at a distance range of 0 to 25 m.

Table 1. Regression coefficients of log road distance for each of the trace elements in PM10 and PM2.5 from road dust

Element	PM10		PM2.5
	β1i (95%CI)	p-value	β1i (95%CI)	p-value
Na	−0.017 (−0.081, 0.048)	0.617	−0.011 (−0.086, 0.063)	0.768
Mg	0.010 (−0.035, 0.055)	0.656	0.023 (−0.022, 0.068)	0.327
Al	0.029 (−0.002, 0.060)	0.070	0.024 (−0.001, 0.048)	0.059
Si	0.026 (−0.002, 0.055)	0.078	0.018 (−0.002, 0.039)	0.084
Cl	−0.089 (−0.157, −0.021)	0.013	−0.113 (−0.176, −0.050)	0.001
K	0.018 (−0.001, 0.037)	0.062	0.006 (−0.010, 0.022)	0.458
Ca	−0.035 (−0.068, −0.002)	0.040	−0.050 (−0.087, −0.012)	0.012
Ti	−0.031 (−0.054, −0.007)	0.012	−0.050 (−0.074, −0.026)	<0.001
V	−0.008 (−0.053, 0.038)	0.745	−0.016 (−0.076, 0.045)	0.619
Cr	−0.064 (−0.093, −0.034)	<0.001	−0.065 (−0.099, −0.032)	<0.001
Mn	−0.017 (−0.053, 0.019)	0.362	−0.052 (−0.082, −0.022)	0.001
Fe	−0.031 (−0.045, −0.016)	<0.001	−0.043 (−0.059, −0.027)	<0.001
Co	−0.071 (−0.119, −0.022)	0.006	−0.042 (−0.109, 0.025)	0.224
Ni	−0.024 (−0.058, 0.010)	0.171	−0.050 (−0.092, −0.008)	0.025
Cu	−0.126 (−0.166, −0.087)	<0.001	−0.141 (−0.187, −0.094)	<0.001
Zn	−0.094 (−0.127, −0.060)	<0.001	−0.109 (−0.143, −0.075)	<0.001
Sr	−0.010 (−0.048, 0.027)	0.588	0.014 (−0.031, 0.059)	0.555
Zr	−0.105 (−0.161, −0.049)	0.001	−0.178 (−0.266, −0.089)	<0.001
Ba	−0.138 (−0.213, −0.063)	0.001	-	-
Pb	−0.064 (−0.121, −0.007)	0.033	−0.063 (−0.132, 0.006)	0.079

Notes. “-“ represents that the element was excluded for mixed model regression analysis; we excluded elements for which the uncertainty was greater than the measurement in more than 20% of samples.

Figure 3. The relationship between log value of relative mass fraction decreases for elements in PM₁₀from road dust and the perpendicular distance from the nearest A12 road in warm season. (a) Fe, (b) Ti, (c) Cu, (d) Zn, (e) Zr, (f) Ba

The dash-dot line represents 95% confidence interval.

Figure 4. The relationship between log value of relative mass fraction decreases for elements in PM_2.5from road dust and the perpendicular distance from the nearest A12 road in warm season. (a) Fe, (b) Ti, (c) Cu, (d) Zn, (e) Zr

The dash-dot line represents 95% confidence interval.