Assessment of indoor and outdoor PM species at schools and residences in a high-altitude Ecuadorian urban center

Highlights

• Z2 (central) zone recorded elevated PM_2.5 levels compared to Z3 (southeast) and Z1 (north) zones.

• Major PM_10–2.5 sources are quarries, unpaved roads, agricultural activities, and soil erosion.

• The three study neighborhoods were impacted by varying traffic densities.

• Indoor-outdoor relationships for PM species were investigated at three schools.

• Central ambient monitoring sites may not be a good surrogate for understanding children's exposure in various exposure settings.

Abstract

An air monitoring campaign to assess children's environmental exposures in schools and residences, both indoors and outdoors, was conducted in 2010 in three low-income neighborhoods in Z1 (north), Z2 (central), and Z3 (southeast) zones of Quito, Ecuador – a major urban center of 2.2 million inhabitants situated 2850 m above sea level in a narrow mountainous basin. Z1 zone, located in northern Quito, historically experienced emissions from quarries and moderate traffic. Z2 zone was influenced by heavy traffic in contrast to Z3 zone which experienced low traffic densities. Weekly averages of PM samples were collected at schools (one in each zone) and residences (Z1 = 47, Z2 = 45, and Z3 = 41) every month, over a twelve-month period at the three zones. Indoor PM_2.5 concentrations ranged from 10.6 ± 4.9 μg/m³ (Z1 school) to 29.0 ± 30.5 μg/m³ (Z1 residences) and outdoor PM_2.5 concentrations varied from 10.9 ± 3.2 μg/m³ (Z1 school) to 14.3 ± 10.1 μg/m³ (Z2 residences), across the three zones. The lowest values for PM_10–2.5 for indoor and outdoor microenvironments were recorded at Z2 school, 5.7 ± 2.8 μg/m³ and 7.9 ± 2.2 μg/m³, respectively. Outdoor school PM concentrations exhibited stronger associations with corresponding indoor values making them robust proxies for indoor exposures in naturally ventilated Quito public schools. Correlation analysis between the school and residential PM size fractions and the various pollutant and meteorological parameters from central ambient monitoring (CAM) sites suggested varying degrees of temporal relationship. Strong positive correlation was observed for outdoor PM_2.5 at Z2 school and its corresponding CAM site (r = 0.77) suggesting common traffic related emissions. Spatial heterogeneity in PM_2.5 concentrations between CAM network and sampled sites was assessed using Coefficient of Divergence (COD) analysis. COD values were lower when CAM sites were paired with outdoor measurements (<0.2) and higher when CAM and indoor values were compared (>0.2), suggesting that CAM network in Quito may not represent actual indoor exposures.

Introduction

The world is becoming increasingly urbanized. It is estimated that by 2050, 2.5 billion people or two-thirds of the planetary population will live in urban areas with most of the increase projected to occur in low- and middle-income countries (LMICs) (United Nations, 2014, United Nations Development Programme (UNDP), 2010). In Latin America, urbanites already comprise nearly eight of every ten residents (UN, 2014). Many heavily populated urban centers, especially those in the Andean region of Latin America and certain Asian countries, are situated at high altitude (>2500 m). The number of high-altitude residents who reside in densely packed, heavily polluted urban centers is steadily rising due to increasing rural-to-urban migration and industrialization (UNEP, 2005).

Urbanization can lead to the deterioration of air quality, smog formation, and pollution-related cardiorespiratory and other adverse health effects (Romieu et al., 2012). This situation is particularly problematic in many urban centers in Latin America (Bell et al., 2006) and other LMICs where air quality is exacerbated by congested traffic, weak vehicular emission regulations, poorly maintained roads, older vehicle fleets, reliance on gasoline and diesel fuels with a high sulfur content, and mountainous topography promoting temperature inversions and pollutant entrapment (Armijos et al., 2015, World Health Organization (WHO), 2014, Health Effects Institute (HEI), 2010, Bogo et al., 2003, Brachtl et al., 2009, Gee and Sollars, 1998, Wang et al., 2003). In addition, the oxygen content of the air in high-altitude urban centers is much lower than that of the sea level. This results in less efficient combustion and greater pollutant release (Armijos et al., 2015).

It is estimated that 600 million urban inhabitants worldwide are currently exposed to high levels of particulate matter (PM) and other air pollutants (Han and Naeher, 2006). The effects of PM emissions on the respiratory and other health outcomes of children have been the focus of many studies during the past two decades (Gehring et al., 2013, Rice et al., 2016, Laborde et al., 2015, Wang et al., 2015). Children appear to be more vulnerable than adults to the adverse health effects of PM and other air pollutants because of their smaller airways and lung size, increased baseline ventilation rates, propensity to mouth breathe, and greater time spent running, jumping, and other aerobic play activities which expose them to greater pollutant loads penetrating deeper into lung tissues (Wright and Brunst, 2013, Bateson and Schwartz, 2008). It is indicative that higher exposure to urban air pollutants is associated with increased blood markers of oxidative stress, systemic inflammation, and endothelial dysfunction in children (Wu et al., 2015, Calderón-Garcidueñas et al., 2009, Kelishadi et al., 2014, Poursafa et al., 2011).

Prior studies have documented the adverse impact of traffic-related air pollutants on cardiovascular health in adults (Adar et al., 2013, Araujo, 2011, Hoffmann et al., 2007, Kunzli et al., 2010). Emerging evidence suggests that close residential proximity to traffic promotes arterial remodeling in children. Iannuzi et al. (2010) reported that Italian schoolchildren living 30–300 m from a major roadway had increased arterial stiffness. More recently, Armijos et al. (2015) reported that long-term exposure to traffic-related pollutants for residents living in close proximity (<100 m) to highly trafficked roadways promotes ultrasound-detectable arterial remodeling measured, as evident in the increased carotid intima-media thickness (cIMT), in healthy schoolchildren living in Quito, Ecuador. However, this research work analyzed only the contribution of residential traffic exposure indicators to cIMT (i.e. residential distance to traffic, distance-weighted traffic density), rather than PM measured at homes and school environments. Furthermore, the analysis of environmental variables suggested that naturally ventilated homes might have allowed for free passage of traffic-related pollutants into interior residential spaces (Armijos et al., 2015). Previous investigations in the Quito Metropolitan District (QMD) have also documented an association between high carbon monoxide levels and elevated carboxyhemoglobin (COHb) levels in a cohort of schoolchildren (Estrella et al., 2005). Brachtl et al. (2009) studied the spatial and temporal variations in polycyclic aromatic hydrocarbons (PAHs) at near roadway sites and recorded a three to six fold increase of PAHs concentrations than that measured at low-traffic residential sites.

Thus, in order to better understand the environmental health indicators that best capture the cardiorespiratory and other health effects of traffic-related PM emissions in urban environments, we conducted assessments of PM pollution in multiple microenvironments, i.e., indoors and outdoors at subject homes and schools. We were also interested in comparing our microenvironmental measurements at these sites with those at nearby central ambient monitoring (CAM) stations since CAM-derived exposure estimates may not accurately reflect the actual exposures of children (Raysoni et al., 2011, Raysoni et al., 2013). Another aim of our study was to compare the gradient in pollutant concentrations in urban Quito neighborhoods with varying traffic densities.