(BRAVO) Study: Final Report. - Desert Research Institute

Final Report — September 2004
Table 10-2 suggests that Factor 1 is related to crustal or soil elements. Factor 1
accounted for approximately 57 percent of the variance. The top 50 loadings of this factor
occur in the southern part of Texas, as shown in Figure 10-1. Factor 2 accounted for about
30 percent of the total variance. Factor 2 suggests a relationship to coal burning due to the
combination of sulfur (S) and hydrogen (H) and the tracer selenium (Se). The top 50
loadings of this factor occur in eastern Texas, with the highest factor scores near the Texas-
Louisiana border, as shown in Figure 10-2. Factor 3 was an undetermined factor that
accounted for about 7 percent of the total variance. Most of the top 50 loadings of Factor 3
were concentrated in southeastern Texas. Factor 4 suggests smelter influence with the
combination of copper (Cu), zinc (Zn) and lead (Pb). It accounted for just under 5 percent of
the total variance. The top 50 loadings of this factor were distributed throughout the study
area, as shown in Figure 10-4.
Turning now to the Big Bend data set, the most significant components of the five
factors (labeled BB1 through BB5) are displayed in Table 10-3. (Compare these factors with
very similar ones that were displayed in Table 6-3. There are minor differences because the
data set used for the factor analyses of Table 6-3 included both 6-hr and 24-hr samples, while
the data set for Table 10-3 included only 24-hr samples.) The selection criterion was again
that the absolute value of the factor loading corresponding to a component was greater than
0.3. Note that the loading for vanadium in Factor BB5 was a negative -0.44.
Table 10-3. Components with the most significant factor loadings for each factor of the Big Bend
data set.
Factor BB1 Factor BB2 Factor BB3 Factor BB4 Factor BB5
Al, Si, K, Ca, Ti, V, Mn,
Fe, Rb, Sr, NO3 – , Na + ,
Mg 2+ , Ca 2+ , O1
H, S, Zn, As, Se, Br,
SO4 2- , NH4 + , O3,
O4, OP, E1
Zn, Pb, Br, NO3 – ,
K + , Ca 2+ , O3, O4,
E1
O1, O2, O3, OP,
E1, E2, E3
Na, V*, NO3 – , Na +
*The factor loading for
V is negative.
Table 10-3 suggests that Factor BB1 was most likely associated with soil, with the
most prominent factor loadings (>0.60) coming from elements such as aluminum (Al),
silicon (Si), potassium (K), calcium (Ca), titanium (Ti), manganese (Mn), iron (Fe), rubidium
(Rb), strontium (Sr), and the magnesium ion (Mg 2+ ). Other variables with significant
loadings on this factor were vanadium (V), nitrate (NO 3 ), the sodium ion (Na + ), and one of
the organic carbon groups, O1. Factor BB1 accounted for 39 percent of the total variance.
Factor BB2, which explained 27 percent of the variance, was sulfate-related, with the
heaviest loadings (>0.90) coming from sulfur (S), hydrogen (H), sulfate (SO 4 ), and ammonia
(NH 4 ). Other important variables loading on this factor were selenium (Se), bromine (Br),
organic carbon groups O2 and O4, and elemental carbon group E1. The inclusion of
selenium suggests this second factor could be associated with coal combustion, a primary
source of emissions that lead to the formation of sulfates, while the presence of organic
carbon fractions implies that another source category may also be involved.
10-6