1. Introduction
The air pollution problem affects both well-developed and developing countries to varying degrees. According to the WHO, 9 out of 10 people breathe air of poor quality [
1]. 5.5 million premature deaths worldwide are attributable to air pollution, which represents the fourth leading risk factor for death worldwide.
The deterioration of air quality has an impact on human health by increasing the incidence of respiratory and cardiovascular diseases [
2,
3,
4], premature death [
5], and cancer [
6,
7]. Respiratory diseases represent one of the major causes of morbidity and mortality [
8]. One billion people suffer from chronic respiratory diseases, including 300 million with asthma and more than 210 million with chronic obstructive pulmonary disease [
9]. As in developing countries, Morocco is experiencing a significant development of its industrial fabric, growing consumption of natural resources and energy, and intensification of means of transport. These factors exert pressure on the different compartments of the environment [
10]. According to the latest estimates of the World Bank, the cost of environmental degradation for Morocco has been evaluated, for the year 2014, at nearly 32.5 billion Moroccan Dirhams, or 3.52% of its GDP [
11]. Water pollution (1.26% of GDP) is the primary vector of environmental degradation, followed by air pollution (1.05% of GDP).
However, air pollution is the most burdensome in the urban context. According to a WHO study on urban air pollution, all the studied Moroccan cities exceed the recommended thresholds for suspended particles (PM10 and PM2.5), namely Casablanca, Marrakech, Tangier, Meknes, Fez, Sale, and Safi [
12]. This finding has also been raised in different urban areas of the Kingdom by studies that have assessed the quality of urban air, focusing on various pollutants [
13,
14,
15,
16,
17,
18,
19,
20,
21,
22,
23]. Thus, the eco-epidemiological studies Casa-Airpol [
24] and Mohammadia-Airpol [
25], have revealed the possible health impacts caused by this form of pollution.
The city of Meknes is among the Moroccan cities affected by air pollution. Studies have revealed air quality degradation due to particles [
26,
27], sulfur oxide, and ozone [
28], which exceeds the standards. The main sources of this urban pollution are multiple: transportation, a dominant factor with a concentration of traffic in the center of the city [
29] and a large fleet of cars [
30]; industry, with units dispersed in the urban space and discharges of variable nature and untreated [
29,
31]; and agricultural production and livestock activities in urban and peri-urban areas [
31]. Local studies have shown that the potential impacts of air pollution are multidimensional, ranging from human health [
32] and urban flora [
33] to the historical monuments of Meknes [
34] classified as UNESCO World Heritage. Considering this situation, local environmental managers have launched a project to set up an air quality monitoring system. However, the planned system has certain limitations and constraints, such as the high cost of the measuring devices, which does not allow for the coverage of the entire urban agglomeration; and the quantitative and punctual aspect on which this system is based and which does not integrate the effects of pollution on human health and urban ecosystems.
Objectives and Research Hypothesis
This work aims to evaluate air pollution levels due to nitrogen dioxide in Meknes city and to study its sanitary impacts.
This objective is based on the scientific hypothesis that a multidimensional and interdisciplinary approach contributes to a better understanding of urban air pollution and its health impacts.
4. Discussions
The analysis of the results shows that for acute respiratory diseases, women (53.23%) were slightly more affected than men (46.76%) with a sex ratio of 1.13. The most affected age group was 15–49 years with 36.11%, while the least represented age group was 50 years and above with 29%. Our results are supported by a study conducted in the city of Meknes covering 30 health centers [
58]. The study conducted by Boularab et al. showed that age is a risk factor in subjects aged 15–49 years and is more important in women (relative risk (RR) ranging from 2.48 to 2.82) than in men (RR ranging from 1.71 to 2.20). The population aged 50 years and older had lower RRs ranging from 1.07 to 1.26, regardless of sex. Age was a protective factor for children aged 5 to 14 years, with RRs significantly below the threshold of 1. The sex ratio (M/F) was generally less than 1.
For asthma attack consultations, women were slightly more affected than men with 53.12% versus 46.85% for a sex ratio of 1.13. The most represented age group was that of 50 years and over, followed by that of 15 to 49 years. In Meknes, Boularab [
58] showed that age is a risk factor for the working population aged 15 years and over with RRs ranging from 1.7 to 4.08. The risk of having asthma attacks was higher in women aged 15–49 years (RR fluctuating from 2.66 to 4.08). The M/F ratios were significantly less than 1. For the 5–14-year age group, age was a protective factor with RRs that ranged from 0.05 to 0.20.
For pneumonia, the age group most affected was 24–59 months, followed by 12–23 months. This result contradicts the results reported by Boularab et al., who noted a decrease in relative risk with increasing age, and the highest risks were recorded in children under 11 months (RR ranged from 2.73 to 5.07) [
58].
Fifty-one point sixty-two percent of the severe pneumonia cases were reported among toddlers less than 11 months old, while those aged 2 years and more represented only 21.22% of the cases. These results are consistent with those reported by Boularab et al. [
58] who showed that age is a risk factor for those under 23 months with RRs ranging from 1.64 to 1.9.
The increased respiratory consultations during the autumn-winter period may be related to temperature variations. The drop in temperature favors the propagation of germs responsible for respiratory infections. It also contributes to the development of molds and dust mites especially in homes that are poorly ventilated and that suffer from a lack of sunlight. These microorganisms release very powerful pneumallergens (spores, mycotoxins, volatile organic compounds and excrements), which can participate in the genesis of asthma in non-asthmatics and the development of asthma attacks in asthmatic people [
59]. Closing windows in winter to increase the temperature inside the home leads to a decrease in ventilation and an accumulation of pollutants. In addition, in cold periods, the increase in household activities, particularly cooking, can lead to an increase in the concentration of indoor pollutants [
60]. Furthermore, the increase in the activity of oil mills from September to March is accompanied by the generation of significant quantities of atmospheric pollutants that can actively participate in the occurrence of asthma attacks and other bronchopulmonary diseases.
The increase in asthma attacks during the spring compared to the summer period may be related to the inhalation of plant pollen since this season is characterized by the flowering and pollination of higher plants.
In the study area, the highest concentrations of NO
2 were found at sites near the city center. Indeed, these roads are characterized by heavy daily traffic, causing a large part of this tracer’s emissions of car proximity pollution [
41,
61]. For the sampling sites installed near the industrial districts of Sidi Bouzekri, Agourai road, Sidi Saïd, El Bassatine, and the Lafarge cement plant, the NO
2 levels measured are below the permissible limit value (40 µg/m
3). These results are consistent with surveys conducted by the Moroccan Ministry of the Environment, which showed that road traffic is responsible for 75% of NO
2 emissions and that the industrial sector does not exceed 25% [
62]. The precipitation rate during the winter campaign has probably led to a decrease in NO
2 levels in the air, given its solubility in water which induces its decomposition into nitrous and nitric acid [
41]. The high temperatures recorded during the summer measurement campaign catalyze the formation of O
3 from NO
2 [
41]. In winter, NO
2 dispersion is localized near the emitting sources due to multidirectional winds and/or a temperature inversion layer a few hundred kilometers above the ground [
58]. During the summer campaign, NO
2 dispersion is characterized by a feathery shape spread towards the southeast of the city and influenced during this period by a dominant wind of moderate intensity coming from the northwest, which ensures maximum dispersion of this tracer [
58]
Nitrogen dioxide is a photoreactive product whose content is controlled by the NO-NO
2-O
3 formation-destruction Chapman reaction cycle under the effect of radiation with a wavelength lower than 400 nm [
58].
This cycle ensures a photostationary equilibrium between NO, NO2, and O3, which is disturbed in the presence of other pollutants such as the volatile organic compounds (VOC) identified as RH, benefiting the conversion of NO to NO2. The OH radicals react with RH and give rise to alkyls that lead to the formation of peroxide radicals through a series of rapid reactions with O2.
These peroxides promote the rapid oxidation of NO to NO
2, increasing nitrogen dioxide near the emission source and ozone at more distant locations [
63].
These reactions explain the low concentrations at the peri-urban site and the concentrations that exceed the limit values at the roadside sites.
The high spatial variability is represented in the maps as a pollution gradient. It shows higher concentrations in the city center, near roads, and at locations and intersections with high traffic loads, which gradually deteriorate towards the periphery of the agglomeration.
The net spatial gradients of NO
2 are a common feature in the various studies of nitrogen dioxide as a pollutant in urban environments [
64,
65]. These gradients are attributed to pollution sources’ location, measurement site type, topography, and road infrastructure [
66]. For example, high NO
2 concentrations at high traffic sites can be attributed to traffic congestion and high NO emissions that rapidly oxidize to NO
2 near the emission sources. However, some NO is oxidized before reaching the tailpipe [
67,
68]. In urban areas, some air pollutants may show more spatial variability than others [
69,
70], showing that the nature of the pollutant plays a crucial role in tracing these gradients.
The photoreactive nature of nitrogen dioxide also explains the very similar average concentrations of the two campaigns. 75% of the days of the first campaign and 58% of the second campaign are clear sky, representing a similar meteorological profile and favorable to the secondary production of NO2 in the absence of rain in the two campaigns. In the presence of rain, nitrogen dioxide leaches from the atmosphere and is transformed into wet deposition as nitric acid [
71]:
The effects of meteorology on the concentration and dispersion of nitrogen dioxide have been revealed in many studies. As in our case study, some of them confirm the absence of a significant difference in average NO
2 concentration between the different study periods [
72,
73]. On the other hand, other studies have revealed a periodic variability attributed mainly to differences in the meteorological profiles of these periods [
74,
75].
According to this study, the city of Meknes appears as a moderately polluted city compared to other urban sites. The average NO
2 concentrations are very similar to those of Elche (Spain), Edinburgh (UK), and Granada (Spain), with almost the same population. These concentrations are in the range of large agglomerations with populations over one million, such as Kanpur (India) and Bamako (Mali) (
Table 7).
These observed disparities between cities could be attributed to differences in urban structure, traffic flows, pollutant emitters, and climatic conditions [
76].
The following table shows nitrogen dioxide concentrations measured worldwide by the passive sampling technique and by automatic monitoring networks in some neighboring countries.
Table 7.
NO2 results were obtained in the city of Meknes compared with other urban agglomerations worldwide.
Table 7.
NO2 results were obtained in the city of Meknes compared with other urban agglomerations worldwide.
Study Area | [NO2] µg/m3 | Study Period | Country | References |
---|
Kocaeli | 14 | July 2006 | Turkey | [77] |
Bouni Region | 14.8 * | Average of 7 months of measurement in 2011 | Algeria | [78] |
Windsor | 23.31 | Average of four 14-day campaigns in February, May, August and October 2004 | Canada | [74] |
Malaga | 22.8 | September 2001 and from December 2001 to February 2002 | Spain | [64] |
Pampelune | 23 | From June 2006 to 2007 | Spain | [69] |
Gothenburg and Mölndal | 23.5 | 7–20 May 2011 | Sweden | [79] |
Asturies | 23.6 | Average of two 7-day campaigns in June and November 2005 | Spain | [80] |
Northern Ireland | 24.3 | Annual average for 1997 | UK | [81] |
Kampala | 24.9 | From 30 June to 13 July, 2014 | Uganda | [82] |
Kocaeli | 25 | January 2007 | Turkey | [77] |
Wales | 27.26 | Annual average for 1997 | UK | [81] |
Scotland | 27.26 | Annual average for 1997 | UK | [81] |
Bamako | 30.45 | From June 2008 to 2009 | Mali | [53] |
Meknes | 30.41 | From 14 July to 28 July 2014 and from 25 December 2014 to 12 January 2015 | Morocco | This study |
Elche | 32 | Average for 2007–2008 | Spain | [83] |
East Anglia | 34.78 | Annual average for 1997 | UK | [81] |
South East England | 34.78 | Annual average for 1997 | UK | [81] |
Edimbourg | 34 | From 2 December 2013 to 13 January 2014 | UK | [73] |
West Midlands | 35.72 | Annual average for 1997 | UK | [81] |
Granada | 36.5 | Average of two campaigns: from July to September 1999 and from December 1999 to February 2000 | Spain | [64] |
Kanpur | 36.9 | February and March 2004 | India | [68] |
Edimbourg | 37 | From 2 August to 13 September 2013 | UK | [73] |
East Midlands | 40.42 | Annual average for 1997 | UK | [81] |
Yourkshire-and-Humber | 42.3 | Annual average for 1997 | UK | [81] |
London | 42.3 | Annual average for 1997 | UK | [81] |
Agadir | 44 | From 20 April to 27 April, 2006 | Morocco | [22] |
Durban | 45.12 | Average of one week in summer 2001 | South Africa | [75] |
Rawalpindi | 55.74 | Annual average for 2008 | Pakistan | [84] |
Dakar | 59.9 | From January 2008 to December 2009 | Senegal | [53] |
Al-ain | 59.3 | From 21 February 2005 to 20 February 2006 | United Arab Emirates | [85] |
Delhi | 68.6 | February and March 2004 | India | [68] |
Sfax | Between 37.6 and 112.8 * | Fall 1996, Winter 1997, Spring and Summer 1998 | Tunis | [63] |
Durban | 110.92 | Average of one week in winter of 2001 | South Africa | [75] |
The highest incidence rates of consultations for acute respiratory diseases were recorded in Béni M’Hamed, Sidi Amar, Aïn Choubik, Al Anouar, Jbabra, and Riad Al Kostani. In Meknes, Boularab [
58] analyzed the spatial pattern of acute respiratory illnesses using the Kulldorff spatial scanning method, which identified eight highly significant (
p < 0.001) high-risk clusters divided into three zones. The first zone is located in the northwest of the city, and includes four clusters centered on the Ras Aghil health sector, with relative risks evolving from 2.3 in 2010 to 5.6 in 2012. The second is located in the center of the city and includes three clusters, two of which are centered on Al Ismailia health sector with relative risks of about 4.2 in 2013 and 4.7 in 2014; the third area represents Al Anouar health sector which recorded a relative risk of 4.1 in 2012 [
58].
The health centers where the highest average annual incidences of asthma attack consultations were recorded are Riad Al Kostani, Al Anouar, Izdihar, El Bassatine, downtown (Ville Nouvelle) and Bab Belkari. Boularab [
58] indicated that the high-risk areas for the occurrence of asthma attacks are located in the north and west of the city of Meknes. The area to the west of the city is composed of two clusters around the Riad health sector, with relative risks of about four. The area to the north of the city is subdivided into three sub-regions. The first is made up of two clusters centered on the Ville Nouvelle health sector, with relative risks of 7.7 and 9.6, respectively; the second sub-region is made up of a cluster centered on the Borj Moulay Omar health sector, with a relative risk of 6.4; as for the last sub-region, it includes a cluster with the lowest relative risk of about 1.8 around the AL Anouar sector.
For severe pneumonia, the highest incidence rates were reported in Zahoua, Ras Aghil, and Riad. Bouarab [
58] revealed the existence of nine high risk clusters, divided into three zones. The first zone is made up of five clusters and is located in the north of the city: two clusters around the Ville Nouvelle health sector with RRs varying between 3.7 and 7.8, one cluster centered on the Ras Aghil health sector with an RR of 5.5 and one cluster around the BMO health sector with an RR of 3.5. The second zone is located in the southwest of the city and is made up of three clusters, two of which are centered on the Touargua health sector with RRs of 14.6 and 6.3, respectively, and one cluster around the Diour Salam health sector with RRs of 4.7 in 2011 and 9.5 in 2013. The last high-risk area is located in the west of the city and is composed of the administrative district health sector with an exceptional RR of 40.8 in 2012.
The highest incidences of pneumonia were recorded in Riad, Izdihar and Bab Rha. Boularab [
58] identified ten high-risk spatial clusters divided into four zones. The first area is located in the north of the city and consists of three clusters: one cluster, with an RR of 1.9, which is centered on the Al Anouar health sector; one cluster around the Izdihar health sector with a relative risk of 2.3; and one cluster with an RR of 3.2 is centered on the El Bassatine health sector. The second high-risk area is located in the southwest of the city and includes three clusters: two clusters around the Jbabra health sector with RRs of 2.6 and 3.1, respectively, and one cluster centered on the Touargua health sector with a relative risk of 2. The third zone is composed of 2 clusters, one centered on the Bab Rha health sector with an RR of 3.8 and the other is around the Riad health sector with an RR of 4. The fourth zone has two clusters centered on the Zahoua health sector with RRs of 3.1 and 3.7, respectively.
Many studies reported associations between NO2 in ambient air and upper and lower respiratory tract diseases, asthma, pulmonary fibrosis, chronic obstructive pulmonary disease and allergic rhinitis [
86].
In 2011, the APHEKOM (improving knowledge and communication for decision making on air pollution and health in Europe) study conducted in 10 major European cities estimated that exposure to vehicular pollution tracers is likely to increase new cases of childhood asthma by 9–25% and COPD by 10–35% in adult subjects over 65 years of age, residing within 150 m of a roadway used by more than 10,000 vehicles per day [
87].
In the PIAMA (prevalence and incidence of asthma and mite allergy) cohort, at the age of four, there was an increased risk of developing several allergic and respiratory health indicators among children exposed to high concentrations of traffic tracers at birth [
87].
A study from the Montreal area in Canada showed that annual and birth exposure to NO
2 was positively associated with the development of asthma. Annual NO
2 exposure was also related to exacerbation of childhood asthma [
88].
Another study conducted in Atlanta, Georgia, during the 1996 Olympic Games showed that an 11–44% decrease in asthma hospitalizations was associated with a 22% decrease in the number of vehicles driven per week [
89].
Lindgren et al. found that adults living within 100 m of a road with more than ten vehicles per minute had a 40% increased risk of asthma and a 64% increased risk of COPD [
90]. Meng et al. (2007) [
91] also noted a 211% increased risk of contracting asthma symptoms in adults living in a high traffic area (>200,000 vehicles/day within 15 m).
Various studies have also shown that NO
2 in ambient air is associated with a significant increase in the risk of emergency room visits and hospitalizations for lower respiratory tract infections [
92,
93,
94,
95]. In parallel, the results of controlled exposure studies in humans and epidemiological studies indicate a causal link between short-term exposure to NO
2 in ambient air and increased asthma-related morbidity [
96,
97,
98,
99,
100,
101]. In children, exposure to air pollution doubles the risk of pneumonia [
102]. Studies have elucidated significant associations between long-term exposure to NO
2 in ambient air and increased hospitalizations for pneumonia [
103].
In Meknes, the relatively high risks of respiratory pathologies observed in the health sectors of the old Medina (Bni M’Hamed, Sidi Amer, Riad Al Kostani, Bab Belkari, and Riad) are probably due to both the emissions of the means of transport and the type of habitat. This sector is characterized by dense traffic, as it contains the place Zine El Abidine, which is the point of convergence of the city’s bus network and public transport. Avenue Mohammed VI, a nerve center of the city (15,000 vehicles/day), the bus station, and the street Dar Smane recorded the highest levels of NO
2. Insufficient sunlight, poor ventilation, and the almost non-existent ventilation of dwellings induce an increase in the indoor relative humidity rate and consequently create favorable conditions for the development and proliferation of a number of microorganisms, including dust mites and molds [
104,
105], which produce very powerful pneumallergens that are strongly implicated in the exacerbation of existing respiratory pathologies and the development of respiratory diseases in unaffected individuals. The accumulation of pollutants from household work (internal pollution) in poorly ventilated homes with ventilation problems is, according to the WHO, responsible for the death of 1.6 million people each year (i.e., one death every 20 s) [
106].
The low incidence of respiratory diseases reported at the Ville Nouvelle health center does not reflect the reality in the field. Indeed, the measurement campaigns conducted during this study (NO
2) and those carried out by Ait Bouh (SO
2, fine and coarse particles) have shown the existence of relatively high levels compared to other sites surveyed in the city. The main causes are the high density of road traffic, especially at the level of FAR Avenue, Bir Anzarane, McDonald’s traffic circle and El Manouni, and the gas stations, which permanently release significant quantities of volatile organic compounds. This can be explained by the social level of the inhabitants, which pushes many of them to consult private practices. In order to know the real incidence of respiratory diseases, it is important to include data from the private sector in this kind of studies, as these diseases are not reportable. In addition, a number of studies have shown a very positive correlation between the social level and the incidence of certain diseases due to exposure to air pollution [
107,
108]. A Canadian study shows that while the risk of being affected by air pollution for high-income subjects with high exposure to air pollution is 33% higher than that of the general Canadian population, it is 162% higher for low-income subjects. Even when subjects from low-income backgrounds are exposed to low levels of pollutants, their relative risk of being affected by air pollution remains higher than subjects from more affluent backgrounds exposed to high levels of air pollutants (82% versus 33%) [
109]. In Rome, Forastiere et al. [
110] have shown that populations with a high socio-economic level, living in the city center, are both more exposed to air pollution and less affected by respiratory pathologies than populations in the periphery, which are less exposed but also less favored in socio-economic terms.
The low incidence rates of respiratory diseases associated with low levels of the pollutant in the three health centers of the commune of Ouislane (Ouislane, Saada, and Al Boustane) may be due to consultations in private practices, visits to emergencies, and the purchase of respiratory drugs directly from pharmacies without having recourse to the competent health structures.
The health centers of Sidi Bouzekri and El Wahda, despite their location near the industrial district of Sidi Bouzekri, present low rates of incidence of respiratory diseases. This is perhaps attributed to the fact that most companies represent storage warehouses, not production units. In addition, the transfer of the headquarters of a large part of the companies to the new industrial districts of Sidi Slimane Moule Al Kifane and Mejjat.