Benzene from traffic

1. Introduction

Background

In most European cities emission from road traffic has become the most important source of local air pollution. Monitoring programmes are in operation in most larger European cities with the aim to follow the development in local air quality and to study the impact of various pollution regulations. The Danish Urban Air Quality Monitoring Programme (LMP) (Kemp and Palmgren, 1999) has been established to provide data for these purposes. As a part of the project on "Air Pollution from Traffic in Urban Areas", conducted with support from the (Danish) National Environmental Research Programme 1992-1996 (SMP) and the project "Traffic Surveillance Programme" funded by the Danish Ministry of Transportation, additional meteorological and air pollution measurements and automatic traffic counts were established in the street of Jagtvej in Copenhagen, close to the permanent LMP pollution measuring station.

Health impacts

Many pollutants are of importance for assessing the adverse impact of air pollution, e.g. NO₂, CO, lead, VOCs and particulate matter. Aromatic VOCs, e.g. benzene, toluene, ethylbenzene and xylenes (BTX), are of great concern due to their adverse health impacts (Field et al., 1992; Finlayson-Pitts and Pitts, 1993; Victorin, 1993). Measurements of BTX have been carried out in central Copenhagen since 1994. Significant correlation was observed between VOCs and CO concentrations, indicating that the petrol fuelled vehicles are the major sources of VOC air pollution in central Copenhagen. Hourly mean concentrations of benzene were observed to reach values of up to 20 ppb, which is critically high according to WHO’s recommendations and the new EU limit values (Hansen and Palmgren, 1995) .

Benzene emission

The emission of benzene from traffic is determined by petrol composition, driving conditions, composition of the car fleet and the percentage of catalytic converters. From year 2000 the content of benzene in petrol must be <1% in EU, a reduction from previous max. value of 5%. Studies have shown that the emission of benzene from petrol-fuelled vehicles depend not only on the benzene content in petrol, but also on the total content of aromatics (Concawe, 1996).

This project

Therefore it was decided to investigate this type of air pollution in more details, especially the relationship between the content of benzene in petrol and the concentration in air. This study was supported by the Danish Environmental Protection Agency.

Benzene in fuel and air

The assessment of emission factors of pollutants are normally based on dynamometer studies with different driving cycles. While dynamometer cycles are essential to establish uniform emission standards for regulatory purposes and for testing of new technologies, they do not necessarily reflect the real on-road driving conditions and the level of maintenance of the actual vehicle fleet. Thus, there is a need for on-road emission estimates of air pollutants from the actual fleet. Such measurements are often performed in road-tunnels (Cadle et al., 1997), but they do not always represent typical urban traffic conditions. Such measurements also often require special measuring campaigns.

Inverse modelling

The relationship between emissions and pollution concentrations can be established by means of an air quality model describing the governing physical and chemical processes. The opposite procedure (an inverse method) can be formulated as: Having air pollution measurements, emissions from traffic can be calculated applying the relationships described by an air quality model. Application of such a procedure using measurements from the extensive monitoring site at Jagtvej and the Operational Street Pollution Model (OSPM) (Berkowicz et al. 1997) is presented here. A somewhat simpler version of the method has previously been applied for estimation of benzene emission factors of the Danish car fleet (Palmgren et al. 1995).

Aims

The report presents a summary of the analysis of petrol sold in Denmark and the air quality measurements at two locations in Denmark, Jagtvej in Copenhagen and Albanigade in Odense. The objectives of the project were, to

	determine the content of benzene in petrol produced and sold in Denmark and record the changes in benzene content,
	monitor the air concentrations of benzene and other aromatic VOCs in streets with dense traffic in Danish towns and determine the emissions from the Danish car fleet, and
	analyse and describe the relationship between the content of benzene in fuel and the benzene concentration in air.