Air Quality & The Environment

What causes Air Pollution?

Air quality can impact on biodiversity and the ecosystems, including land based and aquatic environments.

Sussex is dominated by semi-natural vegetation which accounts for 43% of the total vegetation cover (142214 hectares).

Agriculture accounts for 33% of total vegetation, while only 24% of vegetation is considered as woodlands. Of the woodland, 35% is classified as ancient woodland and therefore considered as part of the sensitive and rare vegetation types.

Land Cover in Sussex (2000) ref: ARMO project

Pollution and plants

Plants are harmed by a variety of air pollutants, either directly or indirectly. Pollutants and issues of particular concern include ground-level ozone (O3), a major component of smog, acid rain, and sulphur dioxide (SO2).

The impact of poor air quality on plants can be acute (rapid and dramatic), chronic (long term), or hidden. Often the symptoms of air pollution are visually similar to the natural aging of leaves in the fall season; however, air pollution can make these conditions appear much sooner than they would otherwise.

In general, plants grow more slowly and can become more vulnerable to disease, pests and difficult environmental conditions such as drought and cold. Some plant species are more sensitive to air pollution than others. This is of particular concern for agriculture and forestry where any reduction in crop growth, productivity or survival can have significant and detrimental impacts on the economic viability of these industries.

Ground level ozone and plants

Plants are very sensitive to increased concentrations of ground-level ozone. Microscopic openings on the surface of each leaf, called stomata, are important in the natural exchange of gases, including the uptake of carbon dioxide. When ozone enters through the stomata, it can interfere with a variety of biochemical and physiological processes, including photosynthesis.

Plant leaf cells become injured and even die as a result of ground-level ozone. This can be seen as small black or brown spots on broad-leafed plants, or yellow (chlorotic) spots on conifer needles.

Sussex-air were involved in the recent EU supported InterregIII project called Air Rives Manche – Ozone, which looked at the impacts of ozone on vegetation in our cross channel region.

For more information contact Sussex-air.

Areas exceeding the AOT40 ozone values (2002-2006) ref: ARMO project

Acid precipitation (rain)

Acid precipitation can harm plants in a variety of ways. Increased soil acidity can decrease the amount of nutrients and essential elements available to plants. Acidity can also hinder the ability of root systems to effectively uptake nutrients. Alternatively, acid precipitation can damage the surfaces of leaves and needles.

quality in a number of ways. As soils become more acidic, their ability to retain many essential nutrients, minerals and elements, such as calcium (Ca), magnesium (Mg) and potassium (K), decreases. As a result, these nutrients, minerals and elements are transported, or leached, by water that flows through the soil, making them less available for land organisms to use.

Water environments

The effect of air pollution on water isn't always visible. Some rivers, lakes or coastal areas may seem clean, but still be polluted because of acid precipitation from rain, snow and particulate matter. Or they may be indirectly harmed when nutrients, elements and heavy metals leach from soils and suspended within the water column.

Water bodies can experience short-term but dramatic acidification, such as when acid precipitation in the form of snow is suddenly released into the water system during the spring melt. This "acid shock" can be lethal for many aquatic organisms such as fish. Alternatively, water bodies can become more acidic over the long term from ongoing exposure to acid precipitation.

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Note:

AOT40 – the parameter used to represent the accumulated dose of ozone

AOT40 (Accumulated dose over a threshold of 40 ppb) is the sum of the differences between the hourly mean ozone concentration (in ppb) and 40 ppb for each hour when the concentration exceeds 40 ppb, accumulated during daylight hours.

The long-term critical level of ozone for crops:

Definition

An AOT40 of 3000 ppb.h accumulated over three months. The critical level is the concentration of pollutants in the atmosphere above which adverse effects occur on sensitive receptors, such as plants, ecosystems or materials according to present knowledge. This critical level was derived experimentally using open-top chambers to expose field-grown wheat to ozone. The data from spring wheat experiments in 6 countries, 10 seasons and with 10 cultivars were used to derive an exposure response relationship with an r2 of 0.88. The AOT40 associated with a 5% reduction in yield, 3000 ppb.h, was accepted as the critical level of ozone for yield reduction in crops.

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