An ozone abatement strategy for Europe?

Health protection should be the priority—but what
are the real health benefits of costly proposals?

Concentrations of ozone in the lower atmosphere are understood to have
an adverse impact on human health, and WHO-Europe have recently
recommended an air quality guideline of 120 µg/m3 (8-hour
average) for Europe. This is a slight relaxation of their earlier advice
that led to the existing Ozone Directive’s health-based threshold of 110
µg/m3 (8-hour average). More stringent guidelines are given by
WHO-Europe to protect vegetation in spite of an apparent lack of
scientific evidence, which would suggest a more considered approach is
justified.

Under the existing Air Quality Assessment and Management and Ozone
Directives, the European Commission is scheduled to come forward with new
proposals to reduce/limit concentrations of ozone to protect health and
vegetation. It is likely that the latest WHO recommendation for health
will be a key consideration in the Commission’s work. This article
explores various aspects that will need to be considered in developing an
ozone strategy for Europe.

The relevant health and environmental effects data for the
establishment of an Air Quality Standard for ozone are summarized in
CONCAWE Report No. 95/60, Determination of air quality standards bands
for ozone.

On the basis of data published up to the end of 1996, there is no
convincing evidence of serious irreversible effects of ozone. Recent
suggestions of mortality associated with exposure to ambient levels of
ozone, based on data from the APHEA study, are not convincing (see CONCAWE
Report 96/61).

US DEVELOPMENTS

Since the analysis performed by WHO-Europe and that performed by
CONCAWE, there has been considerable debate concerning the setting of a
Federal ozone standard for the United States. It is a legal requirement
that when setting such standards, only health impacts can be considered.
Given this requirement, one might expect that the proposed US Standard
would be very similar to the WHO-Europe Guideline but, instead, the latest
US EPA proposal is considerably less stringent. This is illustrated by
Table 1 which compares the stringency of the new US proposal with the
existing Ozone Directive threshold, and the WHO-Europe Guideline using at
least 135 European data series between 1990 and 1994.

Table 1
The US proposal is significantly less
stringent than the current EU-Ozone Directive and WHO-EU values. (Note
that the limits in the table refer to an averaging period of 8 hours.)

Comparison of proposed US EPA
ozone standard with EU-Ozone Directive and WHO-EU
Guideline (8-hour averaging periods)

Concentration
in ambiant
air

maximum number
of exceedances of the
concentrations that
are allowed per
year

percentage of recorded
annual data
series in the EU
not meeting the proposed
requierement*

µg/m3

ppb

EU-Ozone Directive
Health
Protection Threshold

110

55

0

96%

WHO-EU Guideline

120

60

0

84%

US EPA proposals

160

80

4**

32%

NB The Auto/Oil target limit was a 1-hour average of 180
µg/m3 (90 ppb) at a compliance level of 99% (87 hourly
exceedances allowed per year), which equals approximately 170
µg/m3 on an 8-hour basis.

* An annual data series is out of compliance if the
requirements in column two are exceeded on more occasions than in column
three.
** In the US this is averaged over 3 years but, due to a lack
of EU data, the percentage in the final column could only be calculated on
a yearly basis.

ACHIEVABILITY OF THE WHO GUIDELINES

To reduce ozone concentrations, emissions of ozone precursors—nitrogen
oxides (NOx) and Volatile Organic Compounds (VOCs)—must be reduced. In
examining the achievability of any future requirement or target, we first
need to consider what emission reductions are already required under
existing legislation and then to determine what else needs to be done.
This was the approach in the Auto/Oil Programme which found that
compliance with the Auto/Oil ozone target would impose punitive
requirements for reducing emissions from road transport and assumed a
similar reduction in ozone precursor emissions from stationary
sources.

Existing and envisaged legislation for the reduction of VOC and NOx
include:

Acidification Strategy/Large Combustion Plant Directive (NOx)

Ambient Air Quality Assessment and Management Directive/Daughter
Directives

Integrated Pollution Prevention and Control Directive (NOx and VOCs)

Solvents Directive (VOCs)

Stage I control emissions from gasoline distribution (VOCs)

Auto/Oil-1 measures (NOx and VOCs)

UN-ECE LRTAP VOC Protocol

UN-ECE Nitrogen Protocol

Despite the very severe reductions in emissions that these measures
would bring, it is widely recognized that compliance with the WHO-Europe
Guideline is not achievable in the foreseeable future. The Commission has
therefore suggested approaching these ultimate targets by setting interim
objectives (which is commonly referred to as the ‘gap closure’ approach).

THE WAY FORWARD FOR EUROPE

Given the impossibility of achieving the WHO-Europe Guideline, the
Commission’s ‘gap closure’ strategy of setting a long-term, zero-risk
target, which will need to be approached and finally achieved via a series
of intermediate steps, seems to be appealing. However, industry believes
that there are good reasons to argue against this strategy from a
cost-benefit point of view:

The Commission aims at intermediate steps, which reduce by a certain
percentage the number of exceedances in each 150 x 150-km grid square
across Europe. This approach will not, in fact, deliver health benefits
as quickly or as efficiently as a more sophisticated approach. Since the
health impact of ozone relates to the concentration and duration of
exposure, consideration must also be given to reducing absolute
concentrations. Numerous small exceedances are likely to have a lesser
impact on the postulated effect on the population than fewer exceedances
of greater magnitude. Clearly a balance needs to be struck and we should
take time to develop the necessary modelling tools and a better
understanding of the health implications to allow a thorough exploration
of the various strategy options. Europe is currently in danger of
devising a strategy that is dictated by modelling capabilities rather
than the effective protection of health.

In contrast to US legislation which requires the establishment of
zero-risk air quality limits, the EU has to take into account
cost-benefit aspects (in line with the Ambient Air Quality Assessment
and Management Directive) when deriving air quality limit values from
zero-risk WHO-Europe Guidelines. As outlined in previous CONCAWE
Review articles (e.g. Volume 5,
Number 2, October 1996), there is a need for a differentiation between
the risk characterization and the risk management process. ‘The risk
manager should combine and integrate the knowledge generated in the
review of measurement and monitoring methodologies and in the risk
characterization process with the results from the cost-benefit studies,
before deciding on a proposal for a numerical standard. In doing so, the
risk manager will need to understand the degree of certainty associated
with the health-/environmentally-based proposals for standards’. The
importance of all these considerations is recognized by WHO-Europe
itself.

The pace of driving legislation towards the achievement of an
unachievable ultimate target (at least within the foreseeable future)
will automatically enforce BAT measures irrespective of economic
considerations. The proposed ‘gap closure’ approach appears to be in
essence a strategy to apply ‘Best Available Techniques’ (BAT) when
cost-benefit considerations at the intermediate steps are likely to be
of only minor importance.

Given all the considerations above, it is hoped that the WHO-Europe
Guideline for ozone will only be used as a basis for developing a
‘rational’ air quality limit value. This standard should reflect, at the
current stage of knowledge, the best compromise between acceptable
health/environmental risk, compliance costs and other societal needs. Only
if, in the course of time, the basic underlying assumptions used for
setting the ozone standard change due to new scientific evidence on the
health/environmental impact of the pollutant or more cost-effective
emission abatement technology, should the standard be adjusted.