Ozone and traffic in Bilbao (1993-1998)

2000/10/01 Agirre Basurko, Elena | Ibarra Berastegi, Gabriel Iturria: Elhuyar aldizkaria

• Ingurumena

Like many other cities, Bilbao presents important problems of air quality, with ozone (O3), nitrogen oxides (NOx) and carbon monoxide (CO) being the main causes of air pollution, mainly.

Knowing the origin of air pollution in circulation, its control and proper planning of transport systems is essential. Thus, this project analyzes the evolution of traffic and ozone suffered in Bilbao during the years 1993-1998.

As for traffic, the City of Bilbao has 140 traffic study points. Due to the scarcity of data collected at some points, our analysis has been limited to 36 measurement points.

The traffic measures provide us with two different data: on the one hand, the percentage of the passing time of the vehicles on the road and on the other, the number of vehicles passing through each measuring point every ten minutes.

The network of the Basque Government in the metropolitan area of Bilbao has been used in meteorology and air quality. The network has 13 measuring points for the measurement of meteorological parameters and 26 points for the measurement of air quality parameters. In this data, to determine the trends of ozone it is important to eliminate the meteorological effects, for which filters of Kolmogorov-Zurben have been used.

As our work is limited to Bilbao, we have used data from the measurement stations of Elorrieta, Txurdinaga and Mazarredo, the only measuring points that simultaneously received traffic, meteorology and air quality data.

Analyzing traffic data and air quality, two different analyses have been performed.

On the one hand, an annual analysis has been carried out. This annual analysis analyzes the evolution of ozone and average traffic throughout the year.

Emissions affecting ozone production during 1993, 1994 and 1995 have increased year after year. From the end of 1995 the trend is reversed, decreasing ozone levels in 1996. However, in 1997 emissions affecting ozone production increased again (except in Elorrieta), also increasing ozone levels from 1998.

As for traffic data, between 1993 and 1996 internal traffic was reduced by 5%, probably due to the Metro. On the contrary, the entry of traffic from abroad has been increasing and the entry of vehicles in Bilbao has increased.

As of 1997, ozone precursor emissions and ozone levels have increased. The decrease in domestic traffic and the decrease in emissions of ozone precursors have been noticed as a result of the metro, but in recent years there is an upward trend in the years 1993-1994, with levels exceeded. The decrease described after the metro has completely disappeared and if the upward trend of traffic in Bilbao is not corrected, ozone levels will increase in the coming years.

On the other hand, we have analyzed what happens every day of the week and the weekend effect is evident. On weekends, decreased traffic reduces ozone precursors, but increases ozone levels. The reason is that by not decreasing to the same extent nitrogen oxide (NO2) and ozone precursors volatile organic components, the balance for ozone production is broken, causing greater ozone production.

As a culmination of this work, because the air quality we breathe is a concern of all, we want to underline the need for an adequate transport system to reduce the use of the car, since currently traffic is the main responsible for air pollution in Bilbao. Year-on-year evolution of ozone level (1993-1997). Ozone levels per day of the week in Txurdinaga (1993-1998)