Modeling the Effect of Wind Speed and Wind Direction on RSPM Concentrations in Ambient air: A Case Study at Urban Areas in Central India

Abstract

A statistical approach is used to study the impact of wind speed and direction on ambient RSPM concentration at three different urban sampling locations in Nagpur. Directional parameters play an important role in determining the RSPM levels in ambient air. The use of circular statistics in modeling the RSPM concentration using wind direction is suggested. The nonlinear model based on inverse relationship of RSPM concentration with wind speed and sine and cosine of wind direction is used to obtain one-step ahead forecast. The results are compared with benchmark persistence model. Respirable suspended particulate matter (RSPM or PM10 - particulate size less than 10 micron) can reach alveoli region of the lungs and impose serious threat to human health and environment. The high concentrations of RSPM can cause many significant health problems ranging from aggravated asthma to premature death (1). The study of impact of meteorological parameters on particulate matter helps in understanding the role of meteorology in governing the concentration levels. There have been attempt to analyze the effect of wind speed and direction on suspended particulate matter (SPM) concentrations in Delhi (2). Jones et al. (3) analyzed the wind speed dependence of concentrations of RSPM, chloride, sulphate, nitrate, organic carbon, elemental carbon, particle number and NOx in Marylebone, North Kensington and Harwell. Nair et al. (4) found a negative correlation of concentration with wind speed for ionic species of continental origin. Statistical association was observed between RSPM concentration and wind direction in London and Rochester (5). The inverse relationship between wind speed and pollutant concentrations up to some threshold is established in the many studies ((6), (7)). As argued by (3), Gaussian plume models assume the inverse relationship between wind speed and pollutant concentrations. The dependence up to some threshold however cannot be modeled by using Gaussian Plume models. In addition to wind speed, wind direction also governs the levels of concentrations of pollutants. Wind direction is a circular variable and needs the application of directional or circular statistics in modeling the concentrations as a function of wind direction. The study aims at analyzing the meteorological parameters mainly wind speed and wind direction with RSPM concentrations at three urban locations in Nagpur, located in the centre of India. Study of directional parameter needs the application of advance statistical techniques as traditional techniques do not provide adequate inference. Our focus is using circular statistics to assess the importance of wind speed and direction in RSPM variations and using the concept to develop a model to forecast RSPM concentrations in advance. II. STUDY AREA AND DATA COLLECTION Nagpur, situated in the geographical central part of India (210 9'N, 790 6'E 310m ASL), is the 13th largest urban conglomeration in India with a population of around 25 lacs. Recognized as the second green and clean city in India, it has witnessed rapid economic expansion and thereby ever- increasing environmental problems. The major air pollution sources are power plant and automobile exhausts. The area has a tropical wet and dry climate with dry conditions prevailing for most of the year. It receives an annual rainfall of 47.44 from monsoon rains during June to September. Summers are extremely hot lasting from March to June, with maximum temperatures occurring in May. Winter lasts from November to January, during which temperatures can drop below 10°C.