The health effects of air pollutants

Introduction

There are many ways in which air quality is defined. This is normally based on the impact that a pollutant or mixture of pollutants might have on aspects such as human health, visibility, crop damage, damage to the stratospheric ozone layer or acid erosion of buildings.

Poor air quality has been linked to respiratory health effects. The major air pollution episodes of the 1950's and 60's are now thankfully a thing of the past in the UK. This does not mean though that air pollution is not of concern. Rising levels of road traffic, increasing industrial activity and even new homes all represent sources of air pollution.

The focus for outdoor air quality in the UK is on the prevention and minimisation of health effects on persons vulnerable to air pollution. To this end the National Air Quality Strategy provides standards for eight pollutants and a date by when they should be met. Compliance with these standards should indicate that there are no measurable health effects attributable to air pollution.

The three main pollutants of concern in Sussex (particulate matter, ozone and nitrogen dioxide) are discussed in detail below and information about others is given.

Particulate Matter

A lot of focus in the field of air pollution and health is currently centred on fine particulate matter. This very fine dust is capable of penetrating deep into the lungs and has been linked with increased hospital admissions for respiratory disease as well as increased death rates.

Of particular concern is PM10 (dust less than 10 µm in diameter). There are difficulties in controlling this pollutant, as it is derived from naturally occurring sources (such as wind blown soil and plant matter) as well as vehicle and industrial pollutants.

Ozone

Ozone is what is referred to as a 'secondary" pollutant'. That is, there are no direct emissions of ozone into the atmosphere. The ozone is formed as a result of the action of sunlight on other pollutants present in the atmosphere (such as nitrogen oxides and volatile organic compounds). This means that local control of ozone pollution is difficult, and hence it is not one of the pollutants dealt with under the local air quality management regime.

Ozone is a particular problem during summer months (May to August), and concentrations tend to be higher in the south-east than elsewhere in the UK, due to our proximity to continental sources of the chemicals which form ozone.

Exposure to high concentrations of ozone may cause irritation of the eyes and nose, but typical peak levels are more usually associated with airway irritation and related effects.

Nitrogen Dioxide

Nitrogen dioxide is a respiratory irritant, and is also thought to be a sensitiser, which may worsen other conditions such as hay fever. There are a number of oxides of nitrogen present in the atmosphere, but it is nitrogen dioxide which gives rise to health concerns.

Nitrogen dioxide is the pollutant for which there is the most local monitoring. This is because cheap and relatively simple monitoring equipment is available to monitor nitrogen dioxide. Most districts have at least four sites, which participate in a national survey of nitrogen dioxide which has been running for a number of years. More sophisticated monitoring equipment is also in use, giving hourly readings of nitrogen dioxide concentration.

Results from within Sussex show that at certain kerbside (within 1 metre of the road) locations the annual average (40 µg/m3) objective is currently being breached, as well as at a small number of intermediate sites (1-30 m of the road). Data from the DEFRA run Lullington Heath site (near Eastbourne) and in Brighton and Hove suggest that the hourly maximum standard (150 ppb) is not currently exceeded in Sussex.

Other air pollutants

Benzene

Benzene is a known human carcinogen (cancer causing substance), and also contributes to the formation of ozone (summer smog). The major source of benzene is motor vehicle emissions, which nationally account for 67% of emissions with other major sources being the extraction and distribution of fossil fuels and certain industrial processes. Benzene is monitored at a number of sites in Sussex, both at the roadside and in background locations, using passive diffusion tube monitors. These data indicate that the Government air quality objective is currently being met at all sites.

Lead

Lead has been identified as causing acute and chronic damage to the nervous system, effects on the kidneys, joints and reproductive system. At extremely high concentrations lead is toxic. There is currently no local monitoring of lead. Historically, lead was more widely monitored, but concentrations declined dramatically in the late 1980's, early 1990's due to the introduction of unleaded petrol. Leaded petrol has now been completely replaced.

Carbon Monoxide

Carbon Monoxide affects the body by restricting the uptake of oxygen by carboxyhemoglobin. At ambient levels, carbon monoxide may affect concentration, with higher levels leading to more serious nervous system effects. The major source of carbon monoxide is motor vehicle emissions, which nationally account for 97% of emissions. Carbon monoxide data from Brighton and Hove show that the Government air quality objective is currently being met.

Sulphur Dioxide

Sulphur Dioxide is an acute respiratory irritant. It may also be converted through chemical reactions in the atmosphere to secondary sulphate particulate matter. Sulphur dioxide is monitored at Lullington Heath (a rural location), where standards have never been exceeded.