Traffic congestion and ozone precursor emissions in Bilbao (Spain)

GOAL. SCOPE. BACKGROUND: In urban environments, the measured levels of ozone are the result of the interaction between emissions of precursors (mainly VOCs and NOx) and meteorological effects. In this work, time series of daily values of ozone, measured at three locations in Bilbao (Spain), have been built. Then, after removing meteorological effects from them, ozone and traffic data have been analyzed jointly. The goal was to identify traffic situations and link them to ozone levels in the area of Bilbao. METHODS: To remove meteorological effects from the selected ozone time series, the technique developed by Rao and Zurbenko was used. This is a widely used technique and, after its application, the fraction obtained from a given ozone time series represents an ozone forming capability attributable to emissions of precursors. This fraction is devoid of any meteorological influence and includes only the apportion of periodicities above 1.7 years. In the case of Bilbao, the ozone fractions obtained at three locations have been compared on that time scale with traffic data from the area. RESULTS AND DISCUSSION: For the 1993-1996 period, a regression analysis of the ozone and traffic fractions due to periodicities above 1.7 years (long-term fractions), shows that traffic is the main explanatory factor for ozone with R2 ranging from 0.916 to 0.996 at the three locations studied. Analysis of these longterm fractions has made it possible to identify two traffic regimes for the whole area, associated to different profiles of ozone forming capability. The first one favors low ozone forming capability, and is associated with a situation of fluent traffic. The second one shows high ozone forming capability and represents congestion. Joint analysis of raw data of ozone and traffic do not show any clear pattern due to the strong masking effects that seasonal-meteorological effects (mainly radiation) have on the measured ozone signal. If only immission data of ozone are available, as in this case, a comparison between ozone and traffic can only be made on the long-term time scale, since that is the only fraction embedded in the ozone time series that can exclusively be attributed to emissions of precursors. This fact stresses the need to study the different fractions embedded in the time series of ozone measured levels separately. CONCLUSION: Though the coefficients obtained in the regression are only valid for the 1993-1996 period, these traffic regimes represent long-term targets (congestion or fluent traffic) that can inspire policies for a joint management of the traffic and pollution by ozone in the area of Bilbao beyond that period. RECOMMENDATIONS AND OUTLOOK: The results of this work show the need of a joint management of ozone and traffic in Bilbao. Since an accurate knowledge of traffic was not available, the use of emission factors to relate traffic and actual ozone levels has not been possible. For this reason, this study has focused on the long-term fractions of traffic and ozone. In the future, if a more accurate knowledge of traffic is available, it will be possible to find relationships between traffic and ozone on all time scales.     

Use of Faunal Indicators for Assessing the Impact of a Port Enlargement near Bilbao (Spain)

In order to assess the effects of the execution of the Port of Bilbao Enlargement Project, epifauna living on hard substrata and environmental parameters were quantitatively investigated from 1994 to 1996. A programme of repeated non-destructive sampling at 8 stations was carried out during the construction period of a breakwater and the filling operations on the shoreline. A correlation analysis was used as a method to extract potential indicator species of particular environmental conditions measured in the field. We postulate that the remaining species (about 80% of the total species data set), insensitive to any of the investigated environmental factors, were unnecessary for the purposes of assessing the environmental impact caused by the port building works. Classification and ordination techniques were then conducted at two contrasting levels by using the full species data set and the selected faunal indicator data subset. All plots showed separation of sampling sites in 3 major groups, which were easily related to the perturbations caused by a siltation gradient from the estuary mouth. This suggests that the amount of effort required in the enumeration of all the organisms sampled may be dramatically reduced by identifying only faunal indicators of environmental discontinuities in the field. So far, the engineering works developed on the western side of the bay have not caused dramatic temporal changes in species composition, or at least they have not had an effect that was larger than the variations detected among the study sites due to siltation from the estuary mouth.     

Intertidal macrofaunal communities in an intensely polluted estuary

The Bilbao estuary (northern Spain) has suffered a serious environmental deterioration due to industrial and domestic discharges during decades. A total of 21 sampling stations were selected in order to: (1) study the intertidal fauna distribution on both hard and soft bottoms; (2) link this information with the prevalence of certain environmental variables at the sampling sites; and (3) define distinct biological zones with all the information gathered. Up to 50 taxa were identified mainly in the outer estuary with an abrupt decrease upstream. In general, fauna on hard substrates was more diverse, while soft bottom communities exhibited a more consistent structure. Sporadic hypoxic events were recorded in the water column of all the sites studied, which affects the distribution of species. Three major biotic zones are proposed in the estuary. This provides a reliable biomonitoring tool for assessing the effectiveness of a sewerage and remediation scheme ongoing on the river and evaluating the future use of each area in the urban development of the city of Bilbao and conurbation.