An extensive assessment on the distribution pattern of organic contaminants in the aerosols samples in the Middle East

1 Introduction and scope of the review

Today, there is a growing interest in improving air quality by both the general public and individual governments. This interest has prompted an increase in atmospheric pollution research, which is an important complex task. Knowledge of all factors and processes involved in atmospheric pollution such as natural and anthropogenic sources of atmospheric pollution is needed, and some of the factors are the transport, the chemical speciation, physical transformations and dry and wet deposition of the pollutants, and finally their effects on living beings [1]. Nowadays, this concern has been encouraged as an important task in atmospheric pollution research, which is a complex duty demanding knowledge of all the issues and processes involved. The most common issues are as follows: (i) the emission of pollutants to the atmosphere by natural and/or anthropogenic sources; (ii) the transport, the chemical, and physical transformations and deposition of the pollutants (dry and wet), and finally, (iii) their impacts and effects on living beings [2]. These processes are essential and must be monitored from different perspectives and at numerous scales of spatial (molecular, micro-scale, meso-scale, continental, and global) and temporal (less than 1 s to years) [3,4]. Numerous atmospheric pollutants such as volatile organic compounds, polyaromatic hydrocarbons, and polychlorinated biphenyls are of particular interest [4].

Atmospheric pollution is a hot topic in the present era, and wide varieties of pollutants were observed as PM in the atmosphere and the subject is an alarming issue [5,6]. Mineral dust is the main contributor to air pollution in the Middle East (ME), and it is getting worse [7]. ME considerably contributes to the 1,000–2,000 Tg/year range of global dust emissions, along with Asia and Africa [8]. The ME is exposed to high levels of anthropogenic PM in addition to natural dust particles [9,10]. The aerosol contamination consists of natural product chemicals derived from biota; synthetic organic compounds including insecticides, chlorinated hydrocarbons, and lubricants; as well as organic compounds from the usage and combustion of fossil fuels [11,12,13]. Organic contaminant in the aerosol leads to the carcinogenic effect [14]. The dust particles by both natural and anthropogenic activities such as vehicular emission, the burning of bio-wastes, and the industrial revolution interrupt the atmosphere, leading to the Arabian Peninsula (AP) as one of the world’s major sources of aerosol particulate matter (PM) [15,16]. The region’s fine dust has a precise organic molecular composition (e.g., Saudi Arabia and Kuwait). They determined that major portions of the organic chemicals in the region’s fine dust particles came from the combustion of fossil fuels and plasticizers.

Aerosols’ effects on air quality are demonstrated by near-surface concentrations of PM, which include both PM10 and PM2.5 (particles with diameters less than 10 and 2.5 m, respectively). Long-term exposure to PM may result in lung cancer, cardiovascular and respiratory conditions, and early worldwide death [17]. The WHO estimates that outdoor air pollution contributed to 4.2 million premature deaths globally in 2016 (WHO, 2018) [17,18]. The organic component of atmospheric aerosols is not well understood, a few notable instances of its environmental effects serve as indications of its potential significance. It is obvious that a deeper understanding of carbonaceous aerosols in general is required given the relationship between these effects of organic aerosols and the molecular shapes of the organic species. Since the Gulf Cooperation Council (GCC) countries may have quite different internal and external causes of air pollution. The communities in GCC follow the trend of spending more time in the indoor medium due to the humid and warmth environmental conditions [18]. Furthermore, the GCC nations are regarded as emerging nations and are well known for being the center of the majority of the world’s oil reserves and facilities for producing crude oil. Hence, indoor air quality is a major parameter to assess the health quality of the residing people in an environment, which also depend upon the closely related parameters like the current industrial activities, weather conditions, the population index, and the living conditions as well.

2 The major source of organic contaminants to the aerosol

Aerosolized organic matter is a common component of the environment and is made up of numerous different chemicals. The typical sources of organic contaminants include fugitive emissions from industrial processes as well as the contribution of shipping activities in coastal aerosol contamination, natural and anthropogenic emissions from forest fires, volcanic eruptions, incomplete combustion of fossil fuels, wood, agricultural detritus, or leaves [19,20,21,22]. It is believed that two important characteristics that govern how airborne PM affects the health system of the human and eminent characteristics of the atmosphere are its size and chemical constituents of PM2.5 or fine particles. Due to the greater specific area of the fine particles, it resides longer time in the atmosphere, makes easy mobilization, and entrains more hazardous contaminants [23]. In addition, it is crucial to use a variety of methodologies to pinpoint the primary sources of airborne organic pollutants to create effective local control measures. The distribution of probable sources of air pollution has been done thus far using a variety of techniques. The methods like diagnostic ratio are widely used even though it is not complete as the quantitative approach [24,25]. Positive matrix factorization (PMF) as receptor modeling is another method that is frequently used to determine the origins of contaminants. Even without extensive information on source profiles, meteorological circumstances, or the methods by which toxins are transported and incorporated into the environment, which is typically not available, PMF can be utilized to allocate the sources [26].

The major method used for addressing the sources of air pollutants qualitatively involves the calculation of the ratios of molecular diagnostic concentration [24]. Comparing the concentration ratios of pairs of commonly occurring organic species can be used to identify the diversity in organic pollution sources [24]. However, a variety of organic contaminants playing a crucial role in the atmosphere from various source and also tends to have degraded with the prevalent atmospheric oxidants [25,27,28,29]. It is important to identify chemical components in PM for a number of reasons. First of all, target compounds can be used as tracers to determine the main sources of atmospheric particulate matter (PM) [30,31]. Second, according to de Kok et al. [32], characterization of the PM-associated organics includes compounds known for their toxicity, which adds a crucial air quality metric. Third, discoveries of organic contaminants and research into their atmospheric responses have significantly improved our comprehension of secondary organic aerosol production [33]. In more detail, compounds resulting from the condensation of volatile organic species produced from plants as well as vascular plant waxes and pollen are among the substances emitted from fundamental biogenic processes. According to Schauer et al. [30], biologically derived substances make up around 30% of the mass of organic fine particulates; saturated hydrocarbons are the most prevalent. Alkanes with odd carbon values in the C₁₉–C₃₅ range are more frequently released by land-based plants [21]. In addition, biogenic sources have high amounts of n-alkanoic and n-alkenoic acids. On the other hand, anthropogenic sources create a wide range of organic compounds, including combustion [34], industrial activities [35], and fugitive dust sources [36].

3 Distribution pattern of organic contaminants in the aerosol along the ME region

Despite the fact that dust storms over the Kingdom of Saudi Arabia are frequent throughout the year, the worst ones usually happen between February and April when it is cooler [37]. Due to a lack of precipitation, precipitation has a limited impact on aerosol features over KSA; nevertheless, local anthropogenic emissions and dust transport have a significant impact on aerosol properties [22]. There are few studies on the distribution of aerosol organic contamination in the Kingdom of Saudi Arabia along the gulf regions [22,38]. In the eastern region of Saudi Arabia, oil industries contributed to the elevated level of organic contaminants in the aerosol samples [38]. The average level of the predominant organic contaminant in the aerosol samples of Dhahran is low compared to other major cities [22,38,39]. According to the study along the Riyadh, the average levels of organic carbon (OC) and elemental carbon (EC) were in the range of the other data in the ME cities, and the temporal pattern reflects the point source and it is from the local sources. However, OC and EC concentrations varied with the air mass source origin, indicating that regional sources had an impact on carbonaceous aerosol concentrations in addition to fluctuations within Riyadh and its ambiances [40]. Based on the work of Al Othaibi et al. [41], dust storms induce an increase in aerosol concentration throughout the spring and early summer, while lower aerosol concentration was detected during the fall and winter, which is due to reduced dust frequency and greater precipitation rates.

In Saudi Arabia, the usage of pesticides over the past 10 years between 2000 and 2010 has significantly increased up to a total of 3.24 × 10³ tons of pesticides to protect an area of nearly 2.1 million hectares or 15 g/m². The Saudi Arabian climate plays a significant role in the increase in contamination, where it is uncommon in a dry area rainfall, with an average annual rainfall of only 7.2 mm as reported by El-Mubarak et al. [42]. Less than 5% of Saudi Arabia is covered by plantations, making the majority of the country desert as a result; there is a significant amount of wind-borne dust in the air of populated places [42]. Through precipitation and dry deposition, they are eliminated from the atmosphere. More persistent substances, such as endosulfan-I, triallate, lindane, chlorpyrifos, and total dichlorodiphenyltrichloroethanes, can recycle many times [42]. More volatile substances, such as trifluralin and triallate, cannot be effectively eliminated from the atmosphere by precipitation as reported by El-Mubarak et al. [42]. In Saudi Arabia, no research reports on the presence of persistent organic pollutants (POPs) in the ambient air have been reported [42]. The complex interrelated sources and the heavy load of air pollutants are due to accelerated developmental activities and economic growth in Saudi Arabia over the past three decades. Such development included both agricultural and industrial progress. Higher amounts of alachlor, atrazine, simazine, malathion, triallate, and pepulate are discovered here, averaging 242–833 ng/m³. Extremely high concentrations of alachlor, atrazine, simazine, and malathion were discovered, measuring 833, 587, 409, and 358 ng/m³, respectively [43]. The capital city of Saudi Arabia showed a much higher level of POPs than other cities around the Kingdom.

Based on the factor analysis, the composition and source of PM10 and PM2.5 in the Jeddah city have been reported by Khodeir et al. [43]. Four to five causes were discovered, including the combustion of heavy oils, suspended dirt, industrial emissions, vehicle exhaust, and marine aerosol. The overall mean mass concentrations in Jeddah are 28.4 25.4 µg/m³ for PM2.5 and 87.3 47.3 µg/m³ for PM10 based on substantial temporal and spatial variability [44]. On the other hand, PM10 levels are higher during Hajj season, and it is well known that millions of pilgrimages were rushing during this time to the city of Mecca, according to Othman et al. [44]. Munir et al. [45] have shown that the pollutants would contribute to the PM10 concentration in Mecca based on the generalized additive model. The results demonstrated that climatic factors such as temperature and wind speed are responsible for the majority of contributions.

Due to its potential to release a variety of air pollutants, smoking Arabian incense has been recognized in a few studies as the primary cause of indoor air pollution in the United Arab Emirates [46,47]. According to El-Sayed et al. [48], Bakhour (an Arabian incense) is a regularly burned indoor household biomass in Sharjah, United Arab Emirates. Bakhour released wide varieties of potential carcinogenic substances according to the observation from 638 homes’ indoor air samples from Abu Dhabi, Dubai, Fujaira, and Sharja [49]. Air conditioners, culinary activities, and cigarette smoking were identified as the sources of the contaminants [49]. Another practice deeply ingrained in Arabic and UAE culture that could expose people to ultrafine PM is the burning of incense. The physical features of four types of incense frequently utilized by Taoists, Buddhists, Hindus, and Shinto adherents were the subject of an experimental investigation by See et al. [50]. The authors have estimated that the particle number concentrations during incense burning ranged from 1.1 × 10¹² to 2.4 × 10¹² particles/m³. The study conducted by Li et al. [51] highlighted the health-related issues in the UAE with respect to the ozone and PM in the aerosol samples. According to their data, ozone only contributed 1% of deaths in 2007, but PM was responsible for 7% of all fatalities. The daily air monitoring data by Al Katheeri et al. have shown that the trend of changes in the aerosol contaminants is primarily caused by both manmade origin and in situ production along the Al Mirfa power plant in Abu Dhabi.

Numerous measurements of the air levels of organic contamination have been made in major cities all around the world [52,53,54]. The ME region, notably Qatar, does not have numerous findings to endorse the primary source of these pollutants in the aerosol samples. Moreover, the characterizations of these pollutants were also not well documented. Due to the dry nature of the nation and frequent dust storms, the natural causes of air pollution in Qatar can be significant [54]. Dust storms have a negative impact on the country’s air quality and increase the level of pollution. Furthermore, statistically significant climatic warming is occurring on the AP, that is, the lower moisture content in the atmosphere will facilitate the easy movement of dust particles [55,56]. In addition, new research indicates that the AP is experiencing an increase in extreme temperatures and an increase in the number of days that are warmer than average [57]. The most prevalent measured PAH in the dust samples from Qatar’s ACU filters was benzo(k) fluoranthene, which made up 19% of all PAHs. Most ACU dust samples (n = 12 of 13 samples) mostly contained three- and four-benzene ring PAHs (PHE, ANT), as well as four-benzene ring PAHs (PYR, BaA, and CHR). According to the National Toxicology Program 2011, benzo(a) anthracene and chrysene are thought to cause cancer in humans, whereas the other PAHs (PHE, PYR, and ANT) are regarded as organic pollutants. These two substances are commonly found in cigarettes, coke oven emissions, coal, and gasoline exhaust [58,59]. The initial concentrations observed by Mahfouz et al. [60] along the Qatar showed several PAHs in the indoor samples of the house, especially the samples from the filters of the air conditioners. The locations of the observed homes followed the north-south pole pattern of Qatar’s Greater Doha. According to the results from Mahfouz et al. [60], all dust samples, with the exception of one, exhibited a predominance of three- and four-benzene ring PAHs. There was a notable variation of the organic contamination in different locations, and the prime source of these contaminants might not be from the point sources.

Local industrial and vehicle activity could produce fine particles, whereas the dust particles from the marine environment could produce coarse particles [61]. The mean PM2.5/PM10 ratio was also about 0.30, which is the acceptable level of sampling locations impacted by a desert environment, as reported in the Eastern Mediterranean (0.26) [62], Arizona, USA (0.28) [63], and Jeddah, Saudi Arabia (0.33) [43]. Moreover, higher PM2.5/PM10 ratio values were observed in typical urban settings in Zhengzhou, China (0.66) [64], urban areas of Costa Rica (0.55–0.77) [65], and numerous urban settings in France (0.63), Italy (0.65), and the northeastern United States (0.54) [66], as well as across 20 European study areas (0.49–0.74) [67]. The total PAHs along the Qatar region were significantly lesser compared to the urban and semi-urban sites throughout the ME, including those in Iran [68], Saudi Arabia [69], and Iraq [70]. In addition, other places around the world, Egypt [71], Kashmir [72], Pakistan [73], China [74], and Korea [75,76], also reflected a higher level of total PAHs. However, we found PAH concentrations that were comparable to those found at sites in Los Angeles, California [77], northern Lebanon [78], suburban/rural areas of Spain [79], Atlanta, Georgia [80], and a downtown site in Mexico during spring [53].

The study conducted by Khamdan et al. [81] looked at the daily and geographic variations in Bahrain’s ambient air quality. The study found that Bahrain had PM2.5 levels of 51.3 38 µg/m³ and PM10 levels of 181 168 µg/m³, and it came to the conclusion that both of these pollutants had a point source of dust storm, the typical characteristics of the area’s desert, and transboundary airborne effects from southern Iraq that not only affect Bahrain but also affect Kuwait and the Eastern Province of the Kingdom of Saudi Arabia. Doms and Schaettler [82] investigated how the wind drives air pollution in cities and industrial zones close to Oman’s northern shore. Abdul-Wahab et al. [83] looked at how the thermal inversion layer affected air pollution and potential health repercussions. According to the study, there is a strong correlation between the occurrence of four diseases linked to air pollution and thermal inversion. To evaluate the effects of liquid natural gas in Oman, Abdul-Wahab [84] designed a research, and it revealed the contaminants from nitrogen oxides, PM10, and carbon monoxide. The findings demonstrate that the pollutant’s mean concentrations were too low to have an impact on the quality of the air.

Due to the AP’s elevated air quality and the region’s unprecedented overall economic growth and oil and gas boom, the AP has gotten a lot of attention during the past 15 years. Studies on air pollution are still very much in the early stages. The Gulf War’s burning of Kuwait’s oil fields in the year of 1991 had a significant negative effect on the Arabian Gulf region [85] on various aspects. The studies along these regions were performed geographically, and the diurnal pattern sowed the significant levels of organic contaminations, especially the petroleum biomarkers and related organic compounds. Pease et al. [86] identified aerosol sources over the Arabian Sea with a significant level of organic contaminants. An analysis of anthropogenic variables and possible effects on Abu Dhabi has been reported by Böer [87]. The research revealed that livestock was the biggest contributing factor and air pollution the least. According to their analysis, the metropolitan districts of Abu Dhabi were divided into low, medium, and major effect zones.

In Kuwait, three sites, two urban and one desert, were the subject of a 12-month study by Brown et al. [88] in 2004–2005, with an extra 6-month period at one of the locations. The average levels of PM10 on yearly basis were in the range of 65.5–92.5 µg/m³. At the urban locations, the average value of PM2.5 concentrations ranged from 37.5 to 39 µg/m³, while in the desert, it was 31 µg/m³. The mean PM2.5 level should follow the twice level of the US National Ambient Air Quality Standard (NAAQS). White et al. [89] reported that the Gulf war has a significant role in the air drivel transfer of organic pollutants, and it lead to the early death of some of the citizens in the Kingdom of Saudi Arabia as well. The computed mean of PAH values along the Kuwait measured 8.3 ng/m³ (range, 5–13 ng/m³), which is comparable to those found in semi-rural and suburban areas worldwide in good agreement with the data reported by Jaward et al. [90], and the results were in agreement with comparative studies conducted across Europe using the same passive sampling device and deployment period such as sites in Hungary, Greece, and Portugal with 10, 9.7, and 6.7 ng/m³, respectively. The passive samplers along the Kuwait sample mainly sample gas-phase pollutants, and the deployed PUF-disk samplers also sample substances that are primarily related to atmospheric aerosols. Jaward et al. [90] reported this finding for these samplers but found no evidence of a molecular weight-related systematic bias in sampling efficiency. This led them to hypothesize that PUF disks collect particles in this size range with a comparable efficiency to the disks trap vapor-phase PAHs and that the aerosol fraction with which PAHs are primarily associated (diameter, 0.1–1.5 m) flows in the atmosphere mostly as gases. The assessed review reveals the significant distribution of organic contaminants along the ME countries especially the gulf regions due to the industrialization and the whopping level of petroleum production. Moreover, the vehicular emission is also a major contributor to these aspects.

4 Conclusion and future perspectives

Pollution sources over the six nations of the AP (GCC countries) indicate that these nations have similar climatic traits, levels of economic development, and rates of the population growth. The study assessed the level of organic contaminants in the aerosol samples along the ME region with the available data. The review reflected the ubiquitous distribution of organic contaminants in the aerosol samples of houses, offices, cars, and so on. The AP has received a lot of attention over the past 15 years because of the region’s elevated air quality, unprecedented general economic expansion, and oil and gas boom. The major reason behind the unanimous level of organic contaminants along the GCC region is the industrialization with the enormous amount of vehicular combustion. Furthermore, GCC countries are the major oil producers in the world, and it is significantly reflecting the level of organic contaminants in the atmosphere. In the ambient air, PMs of Riyadh showed high concentrations of POPs (PAHs, pesticides, and PCBs) and are favorably compared to other cities in the world. Road traffic, petrochemical industry, agribusiness, and waste burning are responsible for most of the air pollution in Riyadh. Efforts should be made by the authorities to monitor and regulate harmful emissions. Initiatives for research and development toward a clean air act are essential and encouraged. To further understand the PM constituents, source apportionment analysis was carried out for organic contaminants datasets by employing US EPA PMF 5.0.