Radiation Measurements 39 (2005) 213 – 217 www.elsevier.com/locate/radmeas Variation of radon ( 222 Rn) progeny concentrations in outdoor air as a function of time, temperature and relative humidity Kulwant Singh a , ∗ , Manmohan Singh a , Surinder Singh a , H.S. Sahota b , Z. Papp c a Department of Physics, Guru Nanak Dev University, Amritsar 143005, India b Department of Physics, Sri Sai College of Engineering and Technology, Pathankot, Punjab, India c Department of Environmental Physics, University of Debrecen, PO Box 51, Debrecen 4001, Hungary Received 5 March 2004; accepted 29 June 2004 Abstract A sensitive grab sampling technique was used to measure the equilibrium equivalent concentration of radon ( 222 Rn) progeny, EEC Rn , outdoors at Bathinda, Punjab (India), over a period of 6 months. The method was based on the beta counting of aerosol samples collected on glass micro-fiber filters by drawing the air through the filters. Measurements, covering two of the three sessions of the day (morning, afternoon, evening), were performed two times per day at a fixed place at a height of 1.8m above the ground surface. The total average value of EEC Rn was 5.62 Bq m -3 , while the morning, afternoon and evening averages were 9.15, 2.85 and 5.33 Bq m -3 , respectively. Negative correlation was observed for air temperature and EEC Rn , while positive correlation was found for relative humidity and EEC Rn , EEC Rn was higher in winter than in summer. © 2004 Elsevier Ltd. All rights reserved. Keywords: Radon; Radon progeny; Meteorological factors; Outdoor air; Time variation 1. Introduction Study of radon and radon progeny in air is indispens- able, as these deliver the highest radiation dose to human beings among all natural radioactive sources. It has been estimated that inhalation of short-lived radon progeny ac- counts for more than half of the effective dose from natu- ral sources (UNSCEAR, 1993). Airborne concentrations of radon and its progeny vary from time-to-time, depending upon the meteorological conditions, such as temperature, relative humidity, wind speed, rainfall, etc. In the present work the time-to-time variation in the equilibrium equiva- lent concentration of radon ( 222 Rn) progeny, EEC Rn , was ∗ Corresponding author. Tel.: +91-183-258820; fax: +91-183-258819. E-mail address: kulwantsthind@yahoo.com (K. Singh). 1350-4487/$ - see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2004.06.015 measured in the outdoor environment near the students hos- tel of G.J.S. engineering college, Bathinda, over a period of 6 months (January to June, 2003). Bathinda is located in the Punjab State of India at 30 ◦ 10 ′ N and 74 ◦ 58 ′ E degrees. Measurements were performed at a fixed place at a height of 1.8 m above the ground surface for 186 days with two measurements each day covering two of the three sessions (morning, afternoon, evening) of the day. In total, 365 mea- surements were carried out over the investigation period, with 117 measurements in the morning, 123 in the afternoon and 125 in the evening. The time of measurements was con- fined to 05:00–07:00 in morning, 12:00–14:00 in afternoon and 17:00–19:00 in evening. The soil at the measuring site is sandy and the building closest to it is at a distance of 25 m. The weather almost always remained calm during the measurements. A new type of grab sampling method developed by Papp and Daróczy (1997) was used for this purpose. It is based on