Skeena Region EPD

Regional Background

Hudson Bay Mountain near Smithers

Introduction

Skeena Region runs from Endako (near Burns Lake) in the east to Haida Gwaii (Queen Charlotte Islands) in the west; from Kitimat in the south to the Yukon and USA borders in the north. It is 266,441 square kilometres in size. It takes up 29% of all British Columbia and is larger than the entire United Kingdom. Skeena Region is largely populated along the Highway 16 transportation corridor. Highway 16 follows the Endako drainage and the Bulkley River in the east. The Bulkley joins the Skeena at the Hazelton Mountains and passes Terrace on its way to (south of) Prince Rupert on the Pacific Ocean coast.

These and other centres can be divided into:

• the Interior Communities:
  • population under 5,500;
  • the heaviest industry is sawmills; and
• the Coastal Communities:
  • populations of 10,000 - 20,000;
  • industry base of sawmills, smelting, pulp mills, coal and grain

How Meteorology Influences Air Quality

In winter, northwestern North America is dominated by the Mackenzie District's polar anticyclone (a body of moving air of higher pressure than the surrounding air), which produces a continental polar air mass. Offshore, low atmospheric pressures occur, where oceanic heat sources indirectly give rise to the Aleutian low region of air pressure.

The Pacific coast experiences frequent cyclonic activity in winter (unsettled conditions, rain, clouds and wind), with an associated mix of maritime polar and maritime tropical air masses. Such unstable (windy) environments tend to have excellent dispersion characteristics (ability to blow pollution and other substances away). As a result, air quality problems, such as those experienced by Interior communities, tend to be much less frequent or intense in such environments.

In summer, the coast is dominated by the Pacific anticyclone (high pressure), while the Interior moves between the coastal conditions and true continental conditions.

The Bulkley Valley is 200 kilometres inland from North America's west coast. The Coast range prevents (or modifies) maritime influences from extending inland to the valley. Occasionally, the Bulkley Valley has stable air masses. In winter, this is in the form of continental polar air masses, typified by cold, dry air with clear skies and low wind speeds. Clear skies, combined with long winter nights, calm winds, and bright (snow) surfaces reflecting daytime sunlight promote an intense climatological process known as radiative cooling.

Radiative cooling is a process in which the ground surface loses energy (heat) by long-wave radiation at a rate greater than the overlying atmosphere. As a result, the ground surface becomes colder than the atmosphere above.

Also, the atmospheric temperature increases as the altitude becomes higher. This is called a temperature inversion: i.e., the normal atmospheric temperature profile is inverted or turned upside down: Temperature increasing with height is opposite to the "normal" atmospheric temperature profile, in which temperature decreases with altitude.

Skiers on Hudson Bay Mountain near Smithers will recognize this phenomenon in winter, whereby the mountain temperatures are much warmer than valley bottom temperatures. These processes can operate at other times of the year. However, they tend to be less intense than in winter, particularly in summer when days are long and nights are short. When these conditions coincide with high pressure subsidence, very strong temperature inversions may result.

Local topography in the Bulkley Valley can have significant influences on local meteorology and climatology. The surfaces of mountain and hillside slopes cool radiatively in the same manner as the surfaces described above (radiative cooling). The cold air overlying these surfaces is dense (heavy) and will drain down-slope as a fluid (just as water does in a mountain stream).

Thus, cold air accumulates and can build up in valley bottoms. This acts to intensify any radiative temperature inversion set up in the valley. In addition, any smoke up at mountain slope elevation (e.g., from an open burn) can be drawn down into the valley under such conditions.

Mountainous terrain acts to detach valley air from regional air masses. For example, cold air can collect in the Bulkley Valley through radiative cooling and cold air drainage. When a warm front comes in from the Coast, the frontal surface can be detached from the valley bottom because it is forced up by mountains. This results in stable cold air remaining trapped in the valley, with unstable, warm coastal air aloft. Thus, the inversion conditions can be maintained, even intensified, even though the regional air mass has changed. (This is known as an advection inversion.)

Interior Communities

Air contaminants in smoke emissions are the primary source of air pollutants in the Interior valleys of Skeena Region. One of the primary air contaminants comprising smoke is "particulate matter" or "PM " ("particulates.") The smaller particulate matter, known as "fine particulates" are about the same size as bacteria, and can be inhaled deep into our lungs, where they can trigger lung and heart disease, and even cause death.

The Provincial Health Officer has identified fine particulates as the most serious form of air pollution in BC, when it comes to direct impacts on people's health. For more information, see Particulate Matter: Impacts. Also, the Environmental Quality Branch site has several publications on fine particulates and smoke, including: Fine Particulates: What They Are and How They Affect Us.

The Interior experiences outbreaks of continental polar air during the winter months. This air mass of high pressure can be characterized, at times, by a strong radiation inversion (a temperature inversion caused by solar radiation). The result is a very stable atmosphere which can result in the build-up of pollutants in the mountain valleys.

For example, a layer of particulate matter was evident over many interior Skeena Region communities associated with a stagnant air mass in February 1996, including Burns Lake, Decker Lake, Houston, and Smithers. A more recent episode occurred on January 18, 2000, in which where smoke could be seen transported from Houston (view over town), down the Bulkley Valley (shown here from Sunny Ridge), and through Smithers (shown here from Snake Nation Road).

The interior of Skeena Region includes the smoke-sensitive Bulkley Valley. It is on approximately the same latitude as the southern end of Alaska's panhandle and approximately 200 kilometres inland from the Pacific coast. The valley is a major transportation corridor containing the Bulkley River, the Yellowhead Highway (Highway 16), and the CN Railway.

Primary population centres in the valley include the Hazeltons, District of Houston, Town of Smithers, and the Village of Telkwa. Emission sources include open burning (agricultural and land-clearing debris), sawmills, a panel board plant, woodstoves, vehicles, road dust and backyard burning (with the exception of Smithers, which has a municipal bylaw banning this practice).

Coastal Communities

Skeena Region's coastal communities with significant emissions to the atmosphere include Prince Rupert and Kitimat. Terrace, while noncoastal in a geographic sense, is dominated by coastal meteorology. Contaminants of relevance include particulate matter (PM₁₀ and PM_2.5, nitrogen oxides (NO and NO₂), sulphur dioxide
(SO₂), total reduced sulphur (TRS), hydrogen fluoride (HF), and PAHs.

Coastal areas are much less influenced by the arctic air outbreaks and are strongly controlled by maritime influences. Even when arctic outbreaks occur, typical high-pressure stability is rare, as a result of strong outflow winds down the Skeena River. The Kitimat Valley is strongly controlled by the north-south valley axis. Outflow winds dominate during the winter months, taking emissions down the Douglas Channel. Summer months see inflow winds taking emissions up-valley towards Terrace. Valley haze has been observed associated with inflow conditions.

Glossary of Meteorological Terms

Anticyclone: A body of moving air of higher pressure than the surrounding air, in which the pressure decreases away from the centre.

Cyclone: Atmospheric circulations that rotate clockwise in the southern hemisphere, and anticlockwise in the northern hemisphere. Cyclones are areas of lower pressure and generally associated with stronger winds, unsettled conditions, cloudiness and rainfall.

Cyclonic activity: Activity associated with areas of lower pressure: unsettled conditions, winds, clouds and rain.

Convective boundary layer: The unstable boundary layer that forms at the ground surface and grows upward through the day as the ground is heated by the sun and convective currents transfer heat upwards into the atmosphere.

Front: A boundary or transition zone between two air masses of different density, and thus (usually) of different temperature. A moving front is named according to the advancing air mass, e.g., warm front if warmer air is advancing.

Fumigation: A pattern of plume dispersion produced when a convective boundary layer grows upward into a plume trapped in a stable layer. The elevated plume is suddenly brought downward to the ground, producing high surface concentrations.

Radiative cooling: A process by which ground surfaces lose energy (heat) by long wave radiation at a rate greater than the overlying atmosphere. Thus, over time, the ground surface becomes progressively colder than the atmosphere above it.

Subsidence: The slow sinking of air, usually associated with high-pressure areas.

Temperature inversion: The normal atmospheric temperature profile is inverted or turned upside down. Temperature increasing with height is opposite to the "normal" atmospheric temperature profile, in which temperature decreases with altitude.

Thermal turbulence: Up and down movement of air that results from surface heating, and the subsequent rising and sinking of air.

Thermal: Rising body of warm air.

Turbulence: Irregular motion of the atmosphere, as indicated by gusts and lulls in the wind.

updated: may 2006