Economics Letters 77 (2002) 387–392 www.elsevier.com / locate / econbase The income elasticity of non-point source air pollutants: revisiting the environmental Kuznets curve * Neha Khanna Department of Economics and Environmental Studies Program, State University of New York, Library Tower 1004, P .O. Box 6000, Binghamton, NY 13902, USA Received 18 December 2001; received in revised form 29 March 2002; accepted 20 May 2002 Abstract This paper examines the income–pollution relationship for three non-point source pollutants in 1990. Ambient concentrations reported at monitors throughout the US are regressed on median household income and other socio-economic variables for the census tracts in which the monitors were located. Contrary to earlier studies, a u-shaped relationship is obtained.  2002 Elsevier Science B.V. All rights reserved. Keywords: Ambient concentrations; Criteria pollutants; Census tracts; Median household income; Weighted least squares JEL classification: Q01; Q25; Q40 1. Introduction The environmental Kuznets curve (EKC) debate was engendered by Grossman and Krueger (1992, 1995) who posited an inverted u-shaped relationship between environmental degradation and income. Subsequently, a vast empirical literature has emerged, mostly using pooled aggregate data for several countries and pollutants. Only recently has the focus shifted to intra-national level data (e.g. Carson et al., 1997; Vincent, 1997; Berrens et al., 1997; Kahn, 1998; List and Gallet, 1999). Empirical results are generally mixed. This paper extends the analysis by Kahn (1998) that found an inverted u-shaped relationship between California vehicle emissions and median household income. The current analysis uses 1990 ambient concentrations of three non-point source pollutants whose primary source is vehicle *Tel.: 11-607-777-2689; fax: 11-607-777-2681. E-mail address: nkhanna@binghamton.edu (N. Khanna). 0165-1765 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0165-1765(02)00153-2