Variations of PM2.5, PM10 mass concentration and health assessment in Islamabad, Pakistan

Sparse information appears in lack of awareness among the people regarding the linkage between particulate matter (PM) and mortality in Pakistan. The current study is aimed to investigate the seasonal mass concentration level of PM2.5 and PM10 in ambient air of Islamabad to assess the health risk of PM pollution. The sampling was carried out with two parallel medium volume air samplers on Whatman 47 mm quartz filter at a flow rate of 100L/min. Mass concentration was obtained by gravimetric analysis. A noticeable seasonal change in PM10 and PM2.5 mass concentration was observed. In case of PM2.5, the winter was a most polluted and spring was the cleanest season of 2017 in Islamabad with 69.97 and 40.44 μgm−3 mean concentration. Contrary, highest (152.42 μgm−3) and lowest (74.90 μgm−3) PM10 mass concentration was observed in autumn and summer respectively. Air Quality index level for PM2.5 and PM10 was remained moderated to unhealthy and good to sensitive respectively. Regarding health risk assessment, using national data for mortality rates, the excess mortality due to PM2.5 and PM10 exposure has been calculated and amounts to over 198 and 98 deaths annually for Islamabad. Comparatively estimated lifetime risk for PM2.5 (1.16×10-6) was observed higher than PM10 (7.32×10-8).


Introduction
Hastily particulate matter (PM) pollution in the air has been evolved all around the world, predominantly in developing countries. World health organization [1] claimed that high exposure to the particulate matter has potential to reduce projected life expectancies by 1 year which increases up to 5.5 years [2]. Airborne particulate matter emerges from both natural (volcanic eruption, forest fire and weathering of parent material and sea salt) and anthropogenic sources including power plants, internal combustion engines as well as from thermo-degradation process. These particles are known to be air toxins and were the subject of WHO guidelines in 2008 when 24-h maximum thresholds for fine (PM2.5) and coarse (PM10) particulate matter were set at 25 and 50 µgm-3 respectively. The extent of toxicity and residence time of particulate matter in the atmosphere directly associated with their morphology, size and surface area [1]. The literature showed that long persistent in the air and deeper penetration inside lungs makes PM2.5 more toxic than PM10 which cause respiratory and cardiovascular diseases due to short-term exposure and mortality by long-term exposure respectively [3].
The World Health Organization (WHO) reported approximately 360,000 premature deaths in Asia each year due to urban air pollution [4]. Pakistan is the most urbanized region in Asia with approximately 35% population resides in cities and towns which is predicted to increase up to 60% by 2050 [5]. This appears in ever increasing air pollution extent in all major cities of Pakistan including In the same lines, Lahore was reported to be more polluted with average PM2.5 mass concentration than New York City, Seoul, and Hong Kong. In 2001, a joint venture of Pak-EPA and JICA [7] monitoring of air quality of three cities (Rawalpindi, Islamabad, and Lahore) reported higher PM10 concentration in the ambient air than WHO limits i.e. 520, 709 and 895 µgm-3 respectively. Hence the PM10 and PM2.5 mass concentration were very higher than the national environmental quality standards for ambient air with maximum thresholds for PM10 (annual, 120; 24-h, 150 µgm-3) and PM2.5 (annual, 15; 24-h, 35 µgm-3) respectively [4]. So far, Pakistan bears economic health burden equal to 1% of the gross domestic product due to PM which is responsible for 22000 premature deaths among adults and 700 deaths among children in Pakistan [8].
In spite of the fact, monitoring and management of PM are not among the top priority in Pakistan due to insufficient information, inadequate law practices, and poorly managed organizations. Resultantly, little sporadic updates and reports which illustrated the emerging and seriousness of PM pollution in Pakistan could be found in the literature [7]. There is no sufficient work has been done on PM mass concentration in Pakistan, especially on PM2.5 size friction of PM which appears in lack of public awareness and increasing rate of mortality and respiratory diseases in Pakistan.
For a better understanding and measuring the extent of current PM pollution in the ambient air of Islamabad, the present study has been designed to measure PM10 and PM2.5 mass concentration in Islamabad. Apparently, the previous studies showed a significant change in PM mass concentration with a change in the season [9]. Hereby, the results were fourthly optimized by evaluating seasonal trends in change of PM concentration. In addition, it is the first time to measure the PM2. 5  for future studies and will be a good addition to existing data of PM pollution in Pakistan. Furthermore, the air quality index of Islamabad during this period along with health consequence of particulate matter pollution is also discussed in this study.

Sampling Site
The current study was set to find out the PM2.5 and PM10 concentration in the ambient air of Islamabad. Islamabad is a capital city of Pakistan, located at approximately 500 m above sea level All samplings were operated at a medium rate of 100 L/min and lasted for 24 h for each sampler. Total 30 days representative samples (excluding rainy days) were collected from each season. Samples were collected through all seasons of the year, the number at each site appearing in Table 1. After sampling, each loaded filter was stored in a refrigerator below 0°C before gravimetric and chemical analysis.

Gravimetric Analysis
The PM2.5 and PM10 mass were determined by gravimetry. Gravimetric analysis of the filters was performed by weighing sample filters before and after sampling period. Quartz filter papers were equilibrated in a temperature and relative humidity controlled chamber for 24 hours and then weighted using an electronic balance (CPA-26P, Sartorius, German). The mass difference determined attributed to the total suspended particulate matter.

Meteorological information
Meteorological data was received from Pakistan meteorological department and online source (www.wunderground.com).

Results and Discussion
The sampling site represents a typical urban site which is just 3 km away from the Quaid-e-Azam University, a well-known site used in much previous air sampling research works [11]. A sum of 240 samples, 120 samples for each PM2.5 and PM10 was collected which was equally divided into 30 for every season. The rain affected days were not included in our sampling.

PM2.5
The  surrounding areas during these months [12]. Mansha et al. [13] have also reported higher PM2.5 mass concentrations during fall and winter seasons as compared to summer and forest fire in Margalla Hills [6]. Hence PM levels in Islamabad were on the same order of magnitude as previous studies in this capital city [6,7,12,13] and other urban locations in Pakistan [7,14,15], but were significantly higher than in less-populated Asian locations [4].

Meteorological condition during study period
A noticeable change in the PM concentration with a change in season is mainly attributed to a change in meteorological conditions [9]. The stable atmospheric condition with low temperate and high humidity facilitates the accumulation PM [18]. The higher values of PM10 and PM2.5 in winter and autumn in this studies may be directly influenced by the meteorological conditions as the lowest mean temperature 14.5˚C with 44.5% humidity was observed in winter whereas, autumn has the highest humidity 51.5% with mean 37.6˚C temperature. Although autumn observed higher temperature, it was well compensated by frequent rainfall [19], as it received higher average precipitation (126mm) compared to winter (93 mm), summer (88.5 mm) and spring (58mm) respectively. Additionally higher average wind velocity in summer ( 14.5 kmh -1 ) and spring (14 kmh -1 ) dilute air pollution more compare to autumn and winter with 12 and 12.5 kmh -1 respectively.

Air quality index
Air quality index (AQI) is a relevant term used to describe the degree of the health risk of the air pollution and indicates its potential to affect the health. It is divided into 6 groups ranging from 0 to 500: good (0-50); moderate (51-100); unhealthy for sensitive individuals (USG) (101-150); unhealthy (151-200); very unhealthy (201-300) and hazardous (301-500) [20]. In Pakistan, the AQI related to The AQI was calculated by relating PM mass concentrations to the relevant standards (US-EPA) [21]. Table 2. Air quality standards (annual mean mass concentration µgm -3 ).

Health risk assessment
Comparative finding from the observed mean concentrations of PM10 and PM2.5 for all four season ( Fig.3) and the reference and standard concentrations ( Where; LTR is Lifetime risk; β is the coefficient of giving pollutant; Cobs is an observed concentration of giving pollutant and Le is the life expectancy of exposed group.

Premature mortality due to PM2.5 and PM10 exposure
According to world population review, the current population of Islamabad is 1,502,000 persons (males and females). The data of population was compared with the average PM10 and PM2.5 mass concentration of four seasons obtained from current study to estimate premature mortality in Islamabad (Table 4).
Where; PMR is Premature mortality rate; Tp is total population exposed to a pollutant, CDR is crude death rate, Ct is toxic mean concentration (daily*annual) of pollutant defined by WHO and Cobs is observed the concentration of specific pollutant.
The method used to determine the level of premature mortality; the numbers are directly related to the number of people exposed and exposure concentration of PM10 and PM2.5. Thereby, the number of premature mortality will be more in a larger city with a similar concentration of PM, in the case of smaller cities, the number will enhance directly with increasing level of PM concentration. According to reported studies, 865,000 premature deaths are caused every year by air pollution and about 60% of these deaths found occurred in Asia [1].

Conclusion
The current study showed higher particulate matter pollution in Islamabad during the four seasons of 2017. The maximum days from all season have higher PM2.5 and PM10 values than the NEQSAA and WHO. The positive trend has been observed between PM10 and PM2.5 mass concentration; however PM10 values remain higher than PM2.5 in all sampling days. In case of AQI, days with PM2.5 pollution was more compared to PM10. In general, AQI results of PM2.5 from this study addressed winter as the most polluted season in Islamabad for the year of 2017 followed by spring, autumn and summer descendingly. Overall, winter and autumn were observed to be more polluted seasons followed by spring and summer respectively. This study only carries the mass concentration and health consequence with public exposure to particulate matter exposure. The health assessment for the mean mass concentration level of PM2.5 and PM10 observed in this study showed significant incensement in premature mortality and associated lifetime risk in Islamabad. However mass concentration alone is only a part of the threat to life but other chemical species also enhance its effect on life. Thereby, a detailed study has been designed including chemical characterization and source identification. The results of the further investigation will be discussed in future.