Daily variation of radon gas and its short-lived progeny concentration near ground level and estimation of aerosol residence time

Abstract

Atmospheric concentrations of radon ( 222 Rn) gas and its short-lived progenies 218 Po, 214 Pb, and 214 Po were continuously monitored every four hours at the ground level in Jeddah city, Kingdom of Saudi Arabia. The measurements were performed three times every week, starting from November 2014 to October 2015. A method of electrostatic precipitation of positively charged 218 Po and 214 Po by a positive voltage was applied for determining 222 Rn gas concentration. The short-lived 222 Rn progeny concentration was determined by using a filter holder connected with the alpha-spectrometric technique. The meteorological parameters (relative air humidity, air temperature, and wind speed) were determined during the measurements of 222 Rn and its progeny concentrations. 222 Rn gas as well as its short-lived progeny concentration display a daily and seasonal variation with high values in the night and early morning hours as compared to low values at noon and in the afternoon. The observed monthly atmospheric concentrations showed a seasonal trend with the highest values in the autumn/winter season and the lowest values in the spring/summer season. Moreover, and in parallel with alphaspectrometric measurements, a single filter-holder was used to collect air samples. The deposited activities of 214 Pb and the long-lived 222 Rn daughter 210 Pb on the filter were measured with the gamma spectrometric technique. The measured activity concentrations of 214 Pb by both techniques were found to be relatively equal largely. The highest mean seasonally activity concentrations of 210 Pb were observed in the autumn/winter season while the lowest mean were observed in the spring/summer season. The mean residence time (MRT) of aerosol particles in the atmospheric air could be estimated from the activity ratios of 210 Pb/ 214 Pb.

Effectiveness of airborne radon progeny assessment for atmospheric studies

“…Paatero et al, 1998;Sýkora et al, 2017;Winkler and Rosner, 2000) and in Middle East locations (e.g. Ahmed et al, 2004;Mohery et al, 2016). Nevertheless, there are sites where 210 Pb activity concentrations show an opposite behaviour, reaching maxima during summer months (e.g.…”

“…Kim et al, 2000;Sýkora et al, 2017). Aerosol residence times from about 1 to 15 days are reported for Middle East locations using the 210 Pb/ 214 Pb couple, (Ahmed et al, 2004;Mohery et al, 2016); however, the authors report that the longer residence times can be ascribed to the regional weather conditions characterised by hot southerly winds loaded with dust particles. 1999-2002 and 2011-2015 (in hours).…”

“…It is worth recalling that in the literature great discrepancies are typically found in residence times calculated using different parent-daughter couples (Anand and Mayya, 2015;Baskaran, 2011;Jia, 2014;Papastefanou, 2009Papastefanou, , 2006Turekian et al, 1977; and therein cited literature). Indeed, 210 Pb/ 214 Bi, 210 Pb/ 214 Pb, and 210 Pb/ 222 Rn couples often provide residence times of the order of few days up to one week (Aba et al, 2020;Ahmed et al, 2004;Bikkina et al, 2015;Gäggeler et al, 1995;Kim et al, 2000;Mohery et al, 2016;Rastogi and Sarin, 2013;Sýkora et al, 2017), couple 210 Po/ 210 Pb provides much longer residence times, of the order of a month and more (Baskaran and Shaw, 2001;Długosz-Lisiecka and Bem, 2012;Jia, 2014;Kim et al, 2000;Marley et al, 2000;McNeary and Baskaran, 2007). Other couples are rarely used in the literature; e.g.…”