Air pollutant concentrations
The distribution of environmental variable levels (pollutants and weather conditions) during the study period is described in Table 2. Average daily concentrations of both PM10 and PM2.5 were higher and more variable from day to day in winter than in spring. The two PM fractions did not exceed 123 μg/m3 and 100 μg/m3, respectively. The 24 h NO2 city means did not show statistically significant differences by season. The daily variability of CO concentrations, on the contrary, was sensibly higher during the winter than in spring survey. As expected, outdoor O3 levels were higher and more variable during the spring survey, but never exceeded 100 μg/m3. Average 24 h concentrations of SO2 were low and showed little variability both in spring and winter. We decided, therefore, a priori not to consider SO2 further in the analyses. Similarly, we did not include mean daily values of barometric pressure (BarP) in the regression models, due to its negligible daily variability.
In terms of relative concentrations, six out of 8 metals examined were more represented in the fine than in the coarse fraction of outdoor PM; therefore only metal concentrations from the PM2.5 fraction are reported in Table 2. Fe, Zn and Pb were present in sizeable concentrations in outdoor PM2.5 samples, whereas Pt, Cd, V, Cr and Ni were only present in traces.
Correlations among ambient variables are reported in Table 3. Outdoor concentrations of fine (PM2.5) and coarse (PM10–2.5) particulate matter were weakly correlated. Daily mean levels of PM2.5 were directly correlated with barometric pressure, CO and NO2 concentrations, inversely correlated with O3 and temperature, and unrelated to relative humidity. Average daily concentrations of PM10–2.5 were positively correlated with NO2, temperature, and to a lesser extent with O3, inversely correlated with relative humidity, and not correlated with CO. NO2 concentrations were neither correlated with CO, nor with O3. Daily mean levels of CO and O3 showed a strong negative correlation.
Correlations between ambient concentrations of PM2.5 and each metal and between metals were also examined (data not shown). PM2.5 daily means were highly correlated with Zn, Cd and Pb levels (ρ = 0.778, 0.714 and 0.694 respectively), moderately correlated with Cr, Pt, Ni and Fe (ρ = 0.565, 0.491, 0.475 and 0.463 respectively), and not correlated with vanadium concentrations (ρ = 0.151). Fe concentrations were scarcely correlated with both Zn and Pb (ρ = 0.318 and 0.328), and moderately correlated with Pt (ρ = 0.564). Pt was scarcely correlated with Zn and Pb (ρ = 0.299 and 0.421). Zn and Pb concentrations were moderately correlated (ρ = 0.663).
Daily indoor concentrations of PM2.5 (averages of 24 h samples collected at the homes of three subjects per survey) were highly correlated with average ambient PM2.5 (ρ = 0.81, p 2.5 indoor/outdoor ratio was evident in the two seasons. Concordance was higher during the winter survey (ρ = 0.91, p ρ = 0.59, p = 0.01), apparently due to a greater daily variability of ambient PM2.5 concentrations in winter than in spring, and not to home-specific characteristics (Figure 1).
We observed a negative association between ambient PM2.5 and PM10 and respiratory function (FVC and FEV1) in the COPD panel (Table 4). The effect on FVC was evident both at a short lag (24 h) and in relation to cumulative exposures over the previous 24 and 48 hours. The effect on FEV1 appeared only when 72 hours of exposure were accumulated. A FEV1 reduction was also seen with increasing NO2 concentrations during the previous 24 and 48 hours. In the asthmatic panel, we observed decreasing values of FEV1 related to cumulative exposure to NO2 concentrations during the preceding 24, 48, and 72 hours (Table 4). No association between respiratory function indices and average concentrations of any of the pollutants (neither at various lags, nor as cumulative exposure over 48 or 72 h) was observed among IHD patients (Table 4).
In the COPD panel, Zn concentrations were associated with FVC and FEV1 decrements at single 24 h lag and at cumulative 48 h and 72 h lags (Figures 2 and 3). The associations were similar in size but less consistent for Fe and Ni. No statistically significant negative association between concentrations of metals and lung function indices was observed in the asthmatic and IHD panels (data not shown).
In the group of asthmatics, a total of 107 measurements of NO concentrations in exhaled breath were performed. Overall, there was no clear association of the various pollutants with this biological marker of inflammation.