Environment and Resource Management

Atmosphere: Photochemical smog

Author

Phil Kingston, Environmental Protection Agency

Reviewer

Scott McDowall, Environmental Protection Agency

Key findings

Indicators and summary of status

Indicator

Status of indicator

Population growth rate

Increasing

Vehicle kilometres travelled

Increasing faster than population

Exceedences of NEPM Air Quality standards for ozone concentrations (photochemical smog)

Number of exceedences per year of one-hour and four-hour standards are declining.

 

Importance

Photochemical smog is formed in the atmosphere when precursor pollutants including nitrogen oxides (NO X) and volatile organic compounds (VOCs) undergo reactions in sunlight to form smog, of which ozone is the principal component. The haze caused by photochemical smog can also reduce visibility.

The precursor pollutants arise from combustion processes. Motor vehicles are the major source of NO X in urban areas, while biogenic emissions from vegetation are the most significant source of VOCs.

The reactions that produce photochemical smog occur over several hours; the availability of NO X limits the amount of ozone produced and sunlight and VOC concentration influence the rate of production. The control and reduction of pollutant emissions are critical to decreasing the number of episodes of photochemical smog.

Ozone has a detrimental effect on health and the environment. It irritates the respiratory tract when present at concentrations significantly above natural background levels. It may affect vegetation growth and damage materials such as rubber, fabric, masonry and paint, and contributes to a reduction in visibility.

Measurement of ozone concentrations in the atmosphere allows evaluation of the success of strategies to reduce emissions of the key precursors of photochemical smog, thus limiting the occurrence of such events.

Monitoring of ozone is conducted in conjunction with meteorological measurements to identify local weather conditions conducive to the formation of photochemical smog.

Table 3.5 shows the National Environment Protection (Ambient Air Quality) Measure (Air NEPM) standards for ozone (NEPC 2003).

Table 3.5 National Environment Protection (Ambient Air Quality) Measure (Air NEPM) standards

Pollutant

Averaging period

Maximum concentration

2008 goal maximum allowable exceedences

Photochemical oxidants
(as ozone)

1 hour

4 hours

0.10 ppm

0.08 ppm

1 day a year

1 day a year

Source: NEPC 2003

Pressure and condition

The major sources of the precursors of photochemical smog are combustion processes (motor vehicles and power stations) and bushfires. Over the past decade ozone levels in excess of guideline values have almost always been associated with bushfires or burning-off events that have occurred during calm weather conditions.

While some of these sources of precursor pollutant emissions (those from motor vehicles, industry and the burning-off of vegetation under suitable conditions) can be controlled, other natural events (biogenic emissions from vegetation and bushfires, and weather conditions favourable to smog formation) cannot. However, weather conditions can be predicted, and forecasts of potential smog events made.

Rising population and the geographical expansion of population centres are resulting in a corresponding increase in the number of vehicle kilometres travelled (VKT), particularly in south-east Queensland, where the VKT is rising faster than the population (Figure 3.15).

In south-east Queensland, transport contributes over 72% of total NO X emissions, and industry contributes a further 16%. Transport and industry are also the highest anthropogenic sources of VOCs, accounting for nearly one-quarter of VOC emissions across south-east Queensland. Lowering emissions is critical to reducing photochemical smog events. See 'Reducing motor vehicle emissions' below.

Vegetation emits over 60% of VOCs in south-east Queensland, particularly during the summer months when weather conditions are also more favourable to the formation of photochemical smog. Burning of vegetation, whether occurring during controlled agricultural or hazard-reduction burning programs or during uncontrolled events such as bushfires, releases large amounts of both NO X and VOCs into the atmosphere.

Ozone is monitored in south-east Queensland and Gladstone. It is not monitored in other locations because they do not have sufficiently large sources of the key precursors to photochemical smog formation.

In south-east Queensland the number of exceedences of Air Quality Standards is determined largely by the coincidence of controlled burning programs or bushfires with suitable weather conditions, and almost all occasions when the standard was exceeded can be attributed to such burning events. On rare occasions, the presence of calm weather conditions that allow normal emissions from urban sources to build up rather than be dispersed can lead to exceedences. The number of exceedences in the region has shown a steady decline over the past decade (Figure 3.16) .

Ozone has been monitored in Gladstone since 2000, but no exceedences of either the one-hour or four-hour standard have been observed. Industry and vegetation are the major emitters of the key precursors in the region, but prevailing weather conditions have not resulted in any episodes of photochemical smog exceeding guidelines.


Figure 3.15 Growth of population and vehicle kilometres travelled in south-east Queensland, actual figures and projections to 2026
Source: DLGPSR 2005, Qld Treasury 2006, QT 1997

 
Figure 3.16 Trend in exceedences of the one-hour and four-hour average NEPM Air Quality Standards for ozone in south-east Queensland,1996-2006
Source: EPA 1997a, 1998, 2001a, 2001b, 2001c, 2004a, 2004b, 2004c, 2005, 2006

Response

The key to reducing the potential for formation of photochemical smog is to limit the precursor pollutants entering the atmosphere. For motor vehicles this requires that the number of vehicle kilometres travelled and the emissions per vehicle be reduced.

The EPA and Brisbane City Council have collaborated on the South-east Queensland Airshed Study, which, together with information from the EPA expanded monitoring network, the compiling of an emissions inventory and the development of an airshed model, has increased the understanding of the formation and dispersion of photochemical smog. This model will be used to model scenarios for development, and study potential impacts of various strategies for the reduction of pollutants, such as the introduction of ethanol-blended fuels in motor vehicles.

Actions contained in local and regional strategies such as Brisbane City Council's Brisbane Air Quality Strategy and the South East Queensland Regional Air Quality Strategy have laid the foundations for the South East Queensland Regional Plan 2005-2026 to deal with major issues such as urban sprawl, improved public transport networks and reductions in the emission of precursor compounds into the atmosphere (BCC 2004; EPA 1999; DLGPSR 2005).

Hazard-reduction and agricultural burning are the subject of continued efforts to coordinate burning with suitable meteorological conditions using Bureau of Meteorology dispersion models and current air quality from the EPA web-based system to confine burning to periods when conditions are appropriate for dispersion of the pollutants.

Reducing motor vehicle emissions

The reduction of motor vehicle emissions is being achieved though a combination of four main approaches:

Reducing the demand for transport

The Queensland Government's South East Queensland Regional Plan 2005-2026 incorporates a number of major initiatives that will reduce transport demand in south-east Queensland (DLGPSR 2005). They include:

Increasing the use of public transport, cycling and walking

The objective is to make the use of public transport, cycling and walking more attractive as alternatives to private motor vehicle use. In 2006 QT released Easy Steps-a toolkit for local governments to plan, design and promote safe walking-to increase pedestrian accessibility, convenience and amenity.

Initiatives outlined in the Queensland Government's Integrated Regional Transport Plan for South East Queensland (QT 1997), South East Queensland Infrastructure Plan and Program 2006 (DLGPSR 2006) and TransLink Network Plan (QT 2007) include:

Improving the emissions performance of the vehicle fleet

A range of initiatives have been implemented to ensure that existing vehicles have the lowest possible emissions through appropriate maintenance and access to clean fuels, and to encourage the purchase of low-emission vehicles:

Increasing the efficiency of the road network

Reducing traffic congestion has direct economic benefits and also avoids the higher emissions associated with restricted traffic flows. Projects that have begun or are being developed under the Queensland Government's South East Queensland Infrastructure Plan and Program 2006 and Brisbane City Council's TransApex Feasibility Study are aimed at reducing traffic congestion now and into the future and include upgrades and duplication of existing roads, and bypass roads to relieve inner city congestion. New link roads and cross-river bridges are other options being developed (DLGPSR 2006; BCC 2005).

References

BCC 2004, The Brisbane Air Quality Strategy, Brisbane City Council, Brisbane.

BCC 2005, TransApex Feasibility Study, Brisbane City Council, Brisbane.

DLGPSR 2005, South East Queensland Regional Plan 2005-26, Department of Local Government, Planning, Sport and Recreation, Brisbane.

DLGPSR 2006, South East Queensland Infrastructure Plan and Program, Department of Local Government, Planning, Sport and Recreation, Brisbane.

EPA 1997, Ambient Air Quality Monitoring: 1996 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 1998, Ambient Air Quality Monitoring: 1997 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 1999, The South East Queensland Regional Air Quality Strategy, Environmental Protection Agency, Brisbane.

EPA 2001a, Ambient Air Quality Monitoring in Queensland: 1998 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 2001b, Ambient Air Quality Monitoring in Queensland: 1999 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 2001c, Ambient Air Quality Monitoring in Queensland: 2000 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 2004a, Ambient Air Quality Monitoring in Queensland: 2001 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 2004b, Ambient Air Quality Monitoring in Queensland: 2002 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 2004c, Ambient Air Quality Monitoring in Queensland: 2003 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 2005, Ambient Air Quality Monitoring in Queensland: 2004 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

EPA 2006, Ambient Air Quality Monitoring in Queensland: 2005 Annual Summary and Trend Report, Environmental Protection Agency, Brisbane.

NEPC 2003, National Environment Protection (Ambient Air Quality) Measure, National Environment Protection Council, Adelaide.

QG 1998, Environmental Protection Regulation 1998, Queensland Government, Brisbane.

Qld Treasury 2006, Queensland Government Population Projections to 2051: Queensland and Statistical Divisions, 2nd edition, Queensland Treasury, Brisbane.

QT 1997, Integrated Regional Transport Plan for South East Queensland, Queensland Transport, Brisbane.

QT 2007, TransLink Network Plan, Queensland Transport, Brisbane.

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Last reviewed 12 May 2011
Last updated 8 February 2008

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