*2.4. Socioeconomic Deprivation Index*

To characterize the neighborhood socioeconomic deprivation at the census block level, an index was created in a previous study [17] (more details elsewhere by Lalloué et al. [17]). Briefly, Principal Component Analysis (PCA) was used to select 15 variables out of 41 initial socioeconomic and demographic variables provided by the 2006 national census at the census block level. Previous ecological studies have demonstrated this index's ability to capture environment-related socio-spatial inequalities in France [6,18,19]. In order to capture the spatial variability of the pollutants, the socioeconomic index was categorized into 10 groups according to the decile of its distribution.

### *2.5. Health Impact Assessments (HIAs)*

HIAs follow a methodology that requires diverse data sources. We combined information related to: (i) size of the population and level of their exposure (population exposure), (ii) the death rate in our study (baseline health rate), and (iii) dose-response function (the relative risk: RR).

The dose-response function was derived from epidemiological studies assessing the relative risk associated with the observed and/or modelled exposure [20]. In this study, the relative risk comes from WHO recommendations; the dose-response function relating all-cause mortality and long term NO2, PM2.5, and PM10 concentrations is quantified by RR = 1.041, 95% CI [1.019; 1.064], RR = 1.064, 95% CI [1.043; 1.085] and RR = 1.077, 95% CI [1.068; 1.086], respectively for 10 μg/m<sup>3</sup> increase in exposure to the pollutant.

*Int. J. Environ. Res. Public Health* **2019**, *16*, 38

In our study, the health effects were evaluated for hypothetical air pollution reductions, according to WHO recommendations. The guideline values identified for each pollutant were 40 μg/m<sup>3</sup> for NO2, 10 μg/m<sup>3</sup> for PM2.5 and 20 μg/m<sup>3</sup> for PM10.

The benefits of the air pollutant reduction scenarios are expressed in terms of attributable number of deaths per year (ΔY) estimated from the following equation:

$$
\Delta \mathbf{Y} = \mathbf{Y}0 \times \left(\mathbf{1} - \mathbf{e}^{-\beta \times \Delta \mathbf{x}}\right) \tag{1}
$$

Where:

> Y0 is the total number of observed deaths,

Δx is the difference between the yearly observed average of the air pollutant and the reference value (counterfactual), and

β is the natural logarithm of the dose-response function (the relative risk) expressed for a 10 μg/m<sup>3</sup> increase in exposure to the air pollutant (β = ln(RR)/10).

The attributable number of deaths was estimated by AirQ+ software which was developed by the WHO European Centre for Environment and Health (http://www.euro.who.int/en/health-topics/ environment-and-health/air-quality/activities/airq-software-tool-for-health-risk-assessment-ofair-pollution).

Tables 1 and 2 present the input data required by the AirQ+ software for our two different periods: 2004 to 2009 for NO2 (Table 1) and 2007 to 2009 for PM10 and PM2.5 (Table 2).

To conduct an HIA per socioeconomic deprivation class, we used two studies which investigated the associations between all-cause mortality and long term air pollutant exposure by socioeconomic group: a Dutch study investigated NO2 and PM10 across 5 socioeconomic groups [14] and a Italian study investigated NO2 and PM2.5 across only 3 socioeconomic groups [13] (Tables 3 and 4). Therefore, we estimated the attributable death rates separately for each socioeconomic class based on the 5 dose-response functions of the Dutch study and on the 3 dose-responses functions of the Italian study.



Death rate is the ratio between the total number of observed deaths older than 30 years and the total population older than 30 years. The death rate is expressed per 100,000 inhabitants. NO2 value corresponds to the mean of the annual average concentrations of the census blocks included in a given socioeconomic deprivation class. NO2:

nitrogen dioxide. More precisely, values of NO2 are equal to <sup>∑</sup>*Ni*=<sup>1</sup> <sup>∑</sup>*Tj*=<sup>1</sup> *Cij N*∗*T* , where N is the number of census block, T the number of years over the study period, and C the annual average concentrations of NO2 of a given census block (*i*) in a given year (*j*).


**Table 2.** Descriptive statistics by socioeconomic deprivation class over the period 2007–2009. It corresponds to the input data of the HIA for PM10 and PM2.5 exposure.

Death rate is the ratio between the total number of observed deaths older than 30 years and the total population older than 30 years. The death rate is expressed per 100,000 inhabitants. PM10 (idem PM2.5 value corresponds to the mean of the annual average concentrations of the census blocks included in a given socioeconomic deprivation class. PM10: particulate matter 10 μm or less in diameter. PM2.5: particulate matter 2.5 μm or less in diameter. More

precisely, values of PM10 (and PM2.5) are equal to ∑*<sup>N</sup> i*=1 ∑*<sup>T</sup> j*=1 *Cij N*∗*T* , where N is the number of census block, T the number of years over the study period, and C the annual average concentrations of PM10 (PM2.5) of a given census block (*i*) in a given year (*j*).

**Table 3.** Associations between long-term NO2 and PM10 exposure and mortality all-causes by socioeconomic class extracted from the Dutch study [14].


Socioeconomic deprivation class: decile; class 'high' = less deprived versus 'low' = more deprived; HR: Hazard Ratio; LL: lower limit of 95% confidence interval of the hazard ratio; UL: upper limit of 95% confidence interval of the hazard ratio; NO2: nitrogen dioxide; PM10: particulate matter 10 micrometers or less in diameter.



Socioeconomic deprivation class: decile; class 'high' = less deprived (decile 1, 2 and 3) versus 'low' = more deprived (decile 8, 9 and 10); HR: Hazard Ratio; LL: lower limit of 95% confidence interval of the hazard ratio; UL: upper limit of 95% confidence interval of the hazard ratio; NO2: nitrogen dioxide; PM2.5: particulate matter 2.5 μm or less in diameter.
