چكيده لاتين :
1. Introduction
According to the World Health Organization (World Health Organization, 2014),
one eighth of global deaths is because of exposure to air pollution. This is more
than twice the previous estimates and confirm that air pollution is currently the
greatest threat to the health of the urban environment in the world.
Particulate matter is one of the major air pollutants. These particles have sizes
ranging from 0.000002 to 500 microns, whereas particles smaller than 2.5 microns
have significant health and health effects because they are capable of accessing the
respiratory system of the human body.
The purpose of this paper is to use statistical methods such as cluster analysis to
determine homogeneous time intervals of Particulate matter as the main pollutants
of Mashhad. The results can be used by urban planners and decision makers in the
discussion of air pollution management, especially planning for the control of air
pollution and reducing air pollution.
2. Review of Literature
Concerning the use of statistical methods in air pollution discussion Saksena Joshi
and Patil (2002) examined the spatial patterns of air pollution change in New Delhi
by cluster analysis method and concluded that there was no statistically significant
relationship between pollutant concentration and station type. In another study,
Ojeda, Cortina-Januchs, Barrón-Adame, Quintanilla-Domínguez, Hernandez,
Vega-Corona, Ruelas and Andina (2010) applied PFCM to clustering algorithm to
investigate air pollution in Salamanca, Mexico. Also, air pollution in Bangkok,
Thailand, was analyzed using cluster analysis. Using a Geographic Information
System (GIS), they mapped air pollution in the area (Prapassornpitaya, Jinsart, &
Sanguansintukul 2011). To reduce costs and better management of air quality stations in the Kanto region of Japan, Iizuka, Shirato, Mizukoshi, Noguchi, Yamasaki and Yanagisawa (2014) performed cluster analysis on air pollution data and found that NOX and O3 pollutants can be classified into eight clusters. Each cluster has homogeneity in terms of spatial characteristics and temporal behavior.
Ismaili (2018) investigated homogeneous areas of Mashhad air pollution in terms
of particulate matter load over a two year period using GIS and cluster analysis method. Results of this study identified three separate homogenous regions for
Mashhad.
3. Method
In the present study, for the temporal analysis of Mashhad air, 10 air quality
stations located in the city of Mashhad were used. Hourly data of suspended
particles smaller than 2.5 microns (PM 2.5) were collected and arranged in
matrices with temporal and spatial scales. Then a hierarchical cluster analysis was
performed. Euclidean distance method and Ward method were used to calculate the
degree of similarity. The resulting groups were then shown as a dendrogram.
4. Results and Discussion
The results of cluster analysis on PM2.5 data of Mashhad showed that three
clusters or homogenous groups were recognized. The first cluster is distributed
throughout the year. The second cluster with a frequency of 113 days is more midyear. But the third cluster, which represents the highest concentration of suspended
particles, often occurs in the second half of the year, with a frequency of 34 days
per year.
But on a monthly scale, Shahrivar, Aban and Azar are in the first cluster, and
spring months and Mehr in the second cluster. Finally, Tir and Mordad and winter
were clustered to the third group.
Weekdays are divided into two main groups, with Friday alone in one cluster and
other days of the week in the other group. At a lower level, four homogeneous
clusters can be identified. Friday and Sunday are in the first and second clusters,
respectively, Tuesday and Thursday in the third cluster and in the fourth cluster are
Saturday, Monday, and Wednesday.
5. Conclusion
In this study, particulate matters smaller than 2.5 microns were analyzed using
clustering techniques on a scale of days, months, days of a week and hours of a
day. The results of hierarchical analysis by Ward's integration method showed that
365 days of the year can be divided into three separate clusters. Also 12 months of
the year can be placed in 3 clusters.
Months Azar, Aban and Shahrivar are in one cluster, and spring months and Mehr
are in the other cluster. Tir and Mordad and months of winter are in the third
cluster.
Days of the week can be grouped into four categories: Friday and Sunday,
respectively, the first and second clusters, and the third cluster, including Tuesdays
and Thursdays, and finally, Saturdays, Mondays and Wednesdays.
At hourly scale, the results of the study showed that the hours of daylight hours can
be divided into homogeneous periods of dawn, morning, evening, and night. The
lowest air pollution in the city of Mashhad is in the evening cluster (13-17h). Most
of Mashhad air pollution is recorded in the night time, between 18 and 24 hours.
