* Corresponding author. Fax: #351-234-429-290. E-mail address: borrego@ua.pt (C. Borrego). Atmospheric Environment 34 (2000) 4683} 4690 Impact of road tra$c emissions on air quality of the Lisbon region C. Borrego*, O. Tchepel, N. Barros, A.I. Miranda Department of Environment and Planning, University of Aveiro, 3810 Aveiro, Portugal Received 7 September 1999; accepted 8 June 2000 Abstract The main purpose of this paper is to present the study of tra$c emissions impact on the Lisbon region air quality. Two approaches of emission data generation with high spatial and temporal resolution are presented and compared. Main roads were processed as line sources and hot on-road emissions were calculated based on daily mean tra$c and emission factors distinguished for several road classes and vehicle types. Also, the disaggregation of national CORINAIR inventory has been performed on the basis of statistical information of fuel consumption and population density. The comparison of emission data obtained by these two approaches demonstrates a good agreement for total values, but a signi"cant di!erence for spatial distribution of the data. To ensure completeness of the data, to improve their spatial resolution and also to analyse the impact of the tra$c emissions, a combination of the two approaches was applied to generate the emission data used by a photochemical numerical system to simulate the atmospheric circulation and the air pollution pattern in Lisbon under summer meteorological conditions, having di!erent emission scenarios. It was possible to conclude that an air pollution abatement strategy is urgently needed and it should take into account the strong contribution of road tra$c emissions to the Lisbon air pollution levels.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Tra$c emission; Emission inventory; Photochemical modelling; Portugal; Lisbon 1. Introduction Urban areas are characterised by high population den- sity and economic development. The resulting pollutant emissions place an increasing pressure in the air quality of these areas. Whereas in the past the major reasons for poor air quality were industrial activity and domestic heating, nowadays, as a result of the rapid increase in mobility, the major current urban air pollutants come from road tra$c (Sturm et al., 1997). To design an air pollution abatement strategy it is necessary "rst of all to identify pollution sources and to quantify their emissions. In last years the methodology for the generation of emission inventories has experi- enced large progress. However, not much information have been available about the temporal and spatial dis- tribution of the emissions (GENEMIS, 1997) and the available inventories mainly concern annual and/or national data. Generation of episodic emission data as input to numerical model is a crucial task for simulation and analysis of short-term photochemical pollution. The principal purpose of this work is to assess the tra$c emissions impact on the air quality of the Lisbon region, namely in photochemical pollution. However, the relation between emissions and air quality varies through time and space, mainly because of di!erent advection and dispersion conditions and di!erent chemical reactions. A quantitative link between the veri"ed rapid increases in primary pollutants levels and that of tropospheric ozone (O  ) can only be established through simulation models that take into account the current understanding of phys- ical, chemical and dynamic mechanism in lower tropo- sphere. To analyse the impact of tra$c emissions and improve the spatial resolutions, it was used a three- dimensional (3D) model aiming to simulate the great variability of short lifetime ozone precursors, such as nitrogen oxides (NO  ) and non-methane volatile organic compounds (NMVOC), to incorporate the nonlinear pathway of the ozone production. In coastal areas, like 1352-2310/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 0 0 ) 0 0 3 0 1 - 0