Elsevier

Science of The Total Environment

Volume 409, Issue 24, 15 November 2011, Pages 5517-5523
Science of The Total Environment

Short Communication
Forecasting of daily air quality index in Delhi

https://doi.org/10.1016/j.scitotenv.2011.08.069Get rights and content

Abstract

As the impact of air pollutants on human health through ambient air address much attention in recent years, the air quality forecasting in terms of air pollution parameters becomes an important topic in environmental science. The Air Quality Index (AQI) can be estimated through a formula, based on comprehensive assessment of concentration of air pollutants, which can be used by government agencies to characterize the status of air quality at a given location. The present study aims to develop forecasting model for predicting daily AQI, which can be used as a basis of decision making processes. Firstly, the AQI has been estimated through a method used by US Environmental Protection Agency (USEPA) for different criteria pollutants as Respirable Suspended Particulate Matter (RSPM), Sulfur dioxide (SO2), Nitrogen dioxide (NO2) and Suspended Particulate Matter (SPM). However, the sub-index and breakpoint concentrations in the formula are made according to Indian National Ambient Air Quality Standard. Secondly, the daily AQI for each season is forecasted through three statistical models namely time series auto regressive integrated moving average (ARIMA) (model 1), principal component regression (PCR) (model 2) and combination of both (model 3) in Delhi. The performance of all three models are evaluated with the help of observed concentrations of pollutants, which reflects that model 3 agrees well with observed values, as compared to the values of model 1 and model 2. The same is supported by the statistical parameters also. The significance of meteorological parameters of model 3 has been assessed through principal component analysis (PCA), which indicates that daily rainfall, station level pressure, daily mean temperature, wind direction index are maximum explained in summer, monsoon, post-monsoon and winter respectively. Further, the variation of AQI during the weekends (holidays) and weekdays are found negligible. Therefore all the days of week are accounted same in the models.

Highlights

► AQI of criteria pollutants based on the observed values has been estimated. ► Air quality index has been forecasted using three statistical techniques. ► PCA has been applied to reduce the number of predictive variable. ► Autoregressive and PCR models are combined to improve the forecast. ► Daily forecasting of AQI is useful for the general public to protect their health.

Introduction

Air pollution related problems have resulted in an increased public awareness of the air quality in both developing and developed countries (Kurt and Oktay, 2010). There are many air pollutants adversely affecting human health in the polluted air such as carbon monoxide (CO), RSPM, SO2, NO2, SPM, ozone (O3), etc. The high concentration of these pollutants can be life threatening, causing breathing difficulty, headache and dizziness. They may even result in heart attacks (Kunzli et al., 2000). Thus, the authorities advise the monitoring and forecasting of criteria pollutants in the air. The forecasting of air pollutants can be made through models. The Gaussian dispersion models are, generally, used for air quality prediction in most of the air pollution studies. Although, the dispersion models have some physical basis, detailed information about the source of the pollutants and other parameters are not generally known (Chelani et al., 2002). In order to overcome these limitations, the statistical models are used, which facilitate the forecasting of pollutant concentrations (Finzi and Tebaldi, 1982, Ziomass et al., 1995, Polydoras et al., 1998).

AQI is an important task for general public to understand easily how bad or good the air quality is for their health and to assist in data interpretation for decision making processes related to pollution mitigation measures and air quality management. Basically, the AQI is defined as an index or rating scale for reporting daily combined effect of ambient air pollutants recorded in the monitoring sites. Recently, Van den Elshout et al. (2008) gave the review of existing air quality indices. A regression model was also used by Cogliani (2001) for air pollution forecast in cities by an air pollution index highly correlated with meteorological variables. A study of Goyal et al. (2006) is made for daily air quality forecasting of air pollutants in Delhi through ARIMA and multiple linear regression (MLR) models. The most of the air quality forecasting studies present in the literature have been made for individual air pollutants.

The main objective of the present study is to develop forecasting models for predicting the daily air quality indices, which can provide the timely information to the public to take precautionary measures to protect their health.

Section snippets

Study area

Delhi is the capital city of India spread over 1483 km2 with 16.9 million inhabitants in 2007–08. Due to the presence of large number of industries and migration of people from neighboring states, nearly 56.27 lakh vehicles are plying on Delhi roads (Economic Survey of Delhi, 2008–2009). Delhi has one of the highest road densities as 1749 km of road length per 100 km2 in India. Its high population growth rate, coupled with high economic growth rate, has resulted in ever-increasing demand for

Methodology

There are primarily two steps involved for forecasting of daily AQI.

  • i)

    The estimation of AQI through USEPA method using daily observed concentration of air pollutants. In this formulation, the formation of sub-indices of each pollutant and the breakpoints aggregation of sub indices are made according to the Indian National Ambient Air Quality Standard. The results of epidemiological studies are indicating the risk of adverse health effects of specific pollutants. In order to assess the status of

Results and discussion

The daily AQI has been estimated using monitored concentrations of criteria pollutants in all the four seasons over the period from 2000 to 2006. The percentage of very poor and severe descriptors of AQI is found to be 81.52%, 81.51%, 69.54% and 38.04% during summer, winter, post-monsoon and monsoon seasons respectively. As one can see, summer and winter seasons have very poor and severe descriptors of AQI. It can be expected in winter due to worst meteorological scenario. However, the same

Conclusions

The present study focuses on the forecasting of daily air quality in terms of AQI in urban city Delhi. The AQI, based on air quality of air pollutants, is a simple number, easily understandable by general public to know how bad or good air quality is? The methodology of forecasting the AQI through different statistical models has been discussed in details. The three statistical models namely ARIMA, PCR and combination of ARIMA and PCR have been used for forecasting. The performance of all the

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