Ž . Atmospheric Research 57 2001 1–8 www.elsevier.comrlocateratmos Total NO column amount over Athens, Greece in 2 1996–97 H.D. Kambezidis a, ) , A.D. Adamopoulos a , C. Gueymard b a Atmospheric Research Team, Institute of EnÕironmental Research and Sustainable DeÕelopment, National ObserÕatory of Athens, PO Box 20048, GR-11810 Athens, Greece b 2959 Ragis Road, Edgewater, FL 32132, USA Received 2 December 1999; accepted 10 June 2000 Abstract Ž . This paper reports the total NO column TNC measurements performed in Athens, Greece 2 during the period 1996–97. The measurements used a solid-state spectrometer and were based on the spectral absorption of beam solar irradiance in the visible region. This study investigates the diurnal and seasonal variations of the total NO column in the atmosphere above Athens. It is 2 Ž . found to be in the range 1–160 matm-cm average values , with large daily and seasonal variations. The highly probable link between this variability and synoptic conditions over Athens is discussed. q 2001 Elsevier Science B.V. All rights reserved. 1. Introduction Ž . Nitrogen dioxide NO is a variable atmospheric gas that plays a key role in urban 2 Ž . pollution and in the ozone O cycle within both the troposphere and stratosphere. Any 3 increase in NO has sensible effects on each one of these processes. Above a certain 2 tropospheric concentration, it results in the appearance of a typical yellow-brownish Ž cloud that is visible in large polluted cities such as Los Angeles Husar and White, . Ž . 1976 and Athens Mantis et al., 1992 . This cloud usually has harmful effects on public health. Also, this highly reactive cloud creates the necessary conditions for the formation of photochemical smog and tropospheric ozone, themselves detrimental to human health. Many studies on the tropospheric and stratospheric abundance of NO also deal with 2 ) Corresponding author. Tel.: q 30-1-3490119; fax: q 30-1-3490140. Ž . E-mail address: harry@env.meteo.noa.gr H.D. Kambezidis . 0169-8095r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-8095 00 00069-7