Poor air quality and hazardous emissions endanger human life
Air pollution from the burning of fossil fuels for power generation or any other purpose is creating a serious health hazard to residents of the areas nearby. The deterioration of air quality, is said to adversely affect human health, human welfare and the environment.
To address this serious situation, the Fossil Fuel Foundation held a workshop recently which discussed air quality and emissions standards. The workshop also covered the future of the power generation sector in South Africa and was marked by lively discussion and a number of conflicting views.
This article provides a summary of the topics and discussions at the workshop, and draws on other sources for further information related to the topics. The workshop covered both CO2 emissions and air quality, and the two topics were intermixed in sessions, which often caused confusion. This discussion will deal only with air quality effects due to coal fired power stations (CFPS) and focuses on outdoor ambient air quality, although poor indoor air quality can have a greater impact on health in this country.
The workshop covered air pollution from all sources, but focused primarily on emissions from the combustion of solid fuels, mainly from coal fired power stations. Unless otherwise indicated, all references are from presentations made at the workshop.
Sources of air pollution and impact on air quality
In terms of the National Environmental Management : Air Quality Act (Act 39 of 2004) ( NEM: AQA) [1]. Air pollution is defined as “any change in the composition of the air caused by smoke, soot, dust (including fly ash), cinders, solid particles of any kind, gases, fumes, aerosols and odorous substance”.
An alternative definition is more focused: “The presence of substances in air at concentrations, durations and frequencies that adversely affect human health, human welfare or the environment.”
Air pollution components
Pollution can consist of both gaseous and solid matter suspended in the air. The following are the main components considered in emissions from CBPS NEM:AQA
- Sulphur dioxide: Resulting mainly from burning coal but also from other sources
- Nitrous oxides (NOx): Formed in the furnace from nitrogen and oxygen
- PM10: Particulate matter with a diameter <10 μm consisting mainly of fly ash and unburnt carbon, but also of solid compounds formed by combination of other pollutants
- PM 2,5: Particulate matter with a diameter <2,5 μm consisting mainly of fly ash and unburnt carbon, but also of solid compounds formed by combination of other pollutants.
- Ozone: A secondary pollutant formed by the reaction of NOx with volatile organic compounds
Sources of air pollution
Both man-made and natural polluting sources exist. There is no such thing as natural clean or pollutant free air. Natural sources of pollution include aeolian or windborne dust, smoke from natural grassland and forest fires, particles of plant matter such as; pollen, seeds, fibre from decaying or rotting matter, salt from sea spray, nitrous oxide from lightning, ozone and various other items. Man-made pollution can come from sources other than power stations and vehicles. In South Africa urban sources can include rubbish burning, unpaved roads, coal and wood burning stoves, paraffin lamps and candles.
There is also a distinction between ambient (or outdoor) and indoor air pollution. The effect of indoor air pollution is equal to or greater than that of ambient in many developing countries, due to the use of coal and wood for cooking and heating, in low income communities. Legislation can only control ambient air quality, and this article will focus only on ambient.
Fig. 1 shows the estimated contribution of various sources to different types of pollutant found in the air. It is clear that CBPS are major contributors to the levels of particulate matter and SO2.
Fig. 1: Estimated source contributors of major pollutants (FFF).
Effect of emissions and impact on health
The critical issue surrounding air quality is the impact of pollution on human health. Epidemiological studies (ES) conducted worldwide have determined that:
- There is a causal relationship between air pollution and several human health problems
- There is a correlation between the level of pollution and the impact on human health
- The very young and very old members of the population are most affected
The impact on human health is measured in terms of premature deaths, decrease in life expectancy, rate of occurrence of health problems and several other indices. The main health problems which show correlation to or are caused by air pollution are:
- Ischaemic heart disease
- Lung cancer
- Chronic obstructive pulmonary disease
- Stroke
- Lower respiratory infections
The World Health Organisation (WHO) has stated that “small particulate pollution have health impacts even at very low concentrations – indeed no threshold has been identified below which no damage to health is observed. Therefore, the WHO 2005 guideline limits aimed to achieve the lowest concentrations of PM possible” [3]. This does not mean that such a threshold does not exist, but more likely that one cannot be identified. The statement implies that, in the absence of anthropogenic pollution, natural sources of pollution can be harmful to health.
Attempts at setting a standard for air pollution depend on establishing the risks associated with air pollution and the impact of air pollution on public health. Studies have attempted to establish both relative-risk (RR) and exposure – response (E/R) functions for various levels of ambient air quality. There are two schools of thought in ES. The one uses a linear no- threshold (LNT) approach, and the other concludes that the response is non-linear and that there is a threshold. Fig. 2 illustrates the E/R for the two approaches.
Fig. 2: Exposure response curves (FFF).
The use of ES for standards setting is an attempt to estimate or quantify the improvement of health that results from a reduction in air pollution, with an aim of setting target standards. Although results vary from location to location, ES have been able to establish a reasonable degree of correlation between reduction in pollution and reduction in associated health problems, although this is expressed in percentages rather than absolute values.
The problems that exist with ES studies lie mainly in isolating the effect of pollution from the effect of other factors, known as compounding factors. Heart disease and respiratory problems can be caused by other factors which occur concurrently with air pollution. Studies have been criticised in the past for ignoring the impact of these factors, although it has been shown that air pollution can exacerbate these conditions. Studies using concurrent data from sites with different pollution levels have to take into account the variations between sites of the other factors. Studies using the same site with time varying pollution levels have to take into account the fact that the other factors vary with time as well. The WHO has set air quality standards based on a large number of studies and these are generally adopted [3].
Improvement in air quality comes at a cost, and this has to be compared with the benefits achieved. There is no question of the need for air quality improvement, but the imposition of severe standards which achieve no or little improvement in health and entail huge expenditure are counterproductive, and the money could have been used for treatment of the conditions instead of attempting prevention.
There does not seem to be any system in place locally which measures the improvements in health following improvement in air quality, so such efficiency would be difficult to measure. If one takes into account all the confounding factors, such as aging, population movement, diet change, changes in living conditions, it is doubtful whether any exercise to measure impact of improved air quality over any period of time would yield a meaningful correlation, so the only metric to evaluate the measures is the ambient air quality itself. There are large discrepancies between the health effects of power station emissions calculated by different studies.
Regulation and legislation
SA standards are set as regulations under NEM:AQA. There are two standards:
Ambient air quality: This is a measure of the concentration of pollutants at ground level, due from all sources, averaged over a period of time. This is a target figure and is a measure of air quality in an area. It does not indicate the source of pollutants. Determining the contribution of different sources is difficult and is affected by the distance of the sources from the measuring point, the time of day, wind and dispersion patterns etc. Ambient air quality standards are given in Table 2.
| Pollutant | 10 min average |
1h average |
24h average |
Annual average |
| SO2 | 500 μg/m3 | 350 | 125 | 50 |
| NOx | – | 200 | – | 40 |
| PM10 current | – | – | 75 | 40 |
| Total suspended particles (TSP) |
– | – | 300 | 100 μg/m3 |
| PM 2,5 current | – | – | 40 μg/m3 | 20 μg/m3 |
Emission levels –This measures the concentration of pollutants at the source, is enforced by law and is intended to regulate the amount of pollutant emitted by a source. Emissions are measured both time average. In the case of a CBPS the measuring point will be the flue or stack. Emission levels applicable to CBPS specified in NEM:AQA are given in table 2.
Levels stated refer to the daily average value.
|
Pollutant |
Station status |
|
|
Existing |
New |
|
| Sulphur dioxide |
3500 mg/Nm3 |
500 mg/Nm3 |
| Particulate matter |
75 mg/Nm3 |
50 mg/Nm3 |
| Oxides of nitrogen |
1100 mg/Nm3 |
250 mg/Nm3 |
Fig. 2: Ambient air quality and emission standards (FFF).
Experts are of the opinion that a standard for PM10 at these levels is unnecessary as it as little effect on health and should be regarded as an irritant more than a threat to health. PM10 particle do not make it into the inner recesses of the lungs but get trapped in the throat and nose.
Measuring and monitoring
Monitoring of ambient air quality (AQ) is managed by the South African Air Quality information service ( SAAQIS), a division of the DEA. There are a large number of AQ measurement and monitoring systems in operation, operated by different organisations. The SAAQIS produces reports on air quality, available on line, for a number of stations in the database. Data for other stations is available on request. Systems in use range from basic measurements used to report on daily levels of pollution to those used to try to determine the source of pollutants in an area, or the contribution of a particular source to the ambient air quality, using isotopic studies. (more related to academic studies). Air quality is measured as the average over a time period, and studies show that levels can vary in a periodic manner.
Eskom
Eskom operates 18 ambient air quality monitoring stations, mainly in the vicinity of the large coal fired power stations
Government
The National ambient air quality monitoring network (NAAQMN) has 112 ( 2014 figure) government air quality monitoring stations operated by all three spheres of government.
Municipal systems
Several municipalities run air quality monitoring stations within their boundaries.
Universities
NWU runs an air quality monitoring system in conjunction with the DEA, at various sites, mainly located in low income residential areas in the Highveld and Gauteng.
Modelling
Ground based monitoring stations are in short supply and to counter this, modelling is used to predict ambient air quality at the site under study. Modelling makes use of emission sources, dispersion patterns, weather data and satellite imaging as well as other factors to predict the air quality expected at a site. Modelling is useful where new sources of emissions are planned. The CSIR has developed a system of modelling that is being used successfully.
Mitigation
Eskom offset programme
The Department of Environmental Affairs’s air quality offsets guideline (26 June 2015) states that “an offset is an intervention, or interventions, specifically implemented to counterbalance the adverse environmental impact of atmospheric emissions in order to deliver a net ambient air quality benefit within the affected airshed/s.” Eskom runs an offset program which is aimed at replacing coal stoves in low income areas with cleaner heat sources such as gas, aimed at reducing both ambient and indoor air pollution.
Abatement at source
All three major pollutants can be reduced at the source and Eskom has undertaken a program of retrofitting CFPS to reduce all of them. None of the existing Eskom CFPS comply with the existing emission standards. The program consists of the following phases:
- SO2: None of Eskom’s current plant have been designed with SO2 reduction in mind and none of these plants will be able to comply with the 500 mg/Nm3 limit. Kusile will be Eskom’s first flue gas desulphurisation plant FG, with Medupi being retrofitted. SO2 reduction concept studies will consider a range of options from coal beneficiation to post-combustion control technologies (wet, semi-dry and dry) including some emerging mutli-pollutant control technologies such as SNOX, Re-ACT etc.
- NOx: None of Eskom’s current plant have been designed with NOX reduction in mind. NOX reduction concept studies are looking at the following options: Low NOX burners (LNBs), LNBs + over fire air (OFA), selective catalytic reduction (SCR) and selective non catalytic reduction (SNCR .
- Particulate emissions: Particulate emissions have been regulated for some time, Eskom has been aspiring to lowering the impacts over the years. Historically, particulate emissions limits have been based on the abatement technology employed at the specific power plant and revised once the plant has been upgraded or retrofitted with better abatement control equipment. These included:
– Upgrading the electrostatic precipitators (ESPs)
– Addition of flue gas conditioning (SO3)
– Retrofitting of the ESPs with fabric filter plants (FFPs)
With the minimum source emissions standards requiring an eventual maximum emissions of 50 mg/Nm3 for all plant, a number of stations will require another phase of upgrades.
The total cost of the retrofit program could run to >R300-billion. If the full plan is implemented it will result in a 7 to 10% step increase in electricity tariffs. If the partial plan is implemented it will result in a 3% step increase in electricity tariffs.
Impact of greenhouse gas emmisions limitations on air quality.
The two issues are unrelated but the implementation of controls on CO2 emissions can have an unforeseen negative effect on air quality. There are numerous examples this, two of which are given below.
The European diesel disaster
Because diesel vehicles emit less CO2/km than petrol vehicles, Both European and British governments promoted the move to diesel driven vehicles by means of subsidies and tax breaks. Diesel vehicles however emit more pollutants, such as PM, than petrol, and contribute to the growing problem of air pollution in major cities such as London. The approach has been reversed and owners of diesel vehicles now face diesel taxes rather than tax breaks in an attempt to reverse the problem.
The wood burning stove fiasco
The UK government introduced a program to encourage the use of wood burning stoves for heating, as wood is officially carbon neutral, in an attempt to reduce CO2 emissions. The program included subsidies on the price of wood fuel and tax breaks for the purchase of wood burning stoves (WBS) . WBS are “clean”if used properly and if the right wood fuel is used. If not the stoves emit smoke. As a result there are an estimated 1-million WBS in London alone, which contribute greatly to the air pollution problem. The Northern Irish government went to extremes and offered a subsidy of £160 on every £100 spent on wood fuel, without any conditions or restrictions, giving the user a profit of £60 on every £100 spent . The result is predictable. People heated empty rooms, buildings, barns and other unnecessary sites in order to take advantage of the subsidy, costing the government a fortune and adding greatly to the air pollution problem in the process.
References
[1] DEA: “The national environmental management: air quality act (Act no 39 of 2004), Standards and regulations”, www.saaqis.org.za/documents/NEM-AQA%20Booklet_2014.pdf
[2] A Marquard: “South Africa and the G20: where do we stand on greenhouse gas emissions?”, UCT news, 11 July 2017.
[3] WHO: “Ambient (outdoor) air quality and health”, WHO fact sheet.
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