Meteorological parameters & air pollution PDF

Meteorological parameters & air pollution Department of Chemical Engineering Dr. Haripada Bhunia  Presentation Outline  Introduction  A brief history  What is atmosphere?  Boundaries of the atmosphere...

Meteorological parameters & air pollution Department of Chemical Engineering Dr. Haripada Bhunia  Presentation Outline  Introduction  A brief history  What is atmosphere?  Boundaries of the atmosphere Earth’s atmosphere,  Horizontal atmospheric motion Principles of  Equatorial heating and polar cooling meteorology and  Atmospheric circulation The effect of the earth's rotation  Influence of the ground and the sea  Vertical atmospheric motion  Air density change with temperature  Air density change with pressure  Meteorological parameters  Conclusions Department of Chemical Engineering, TIET November 22, 2024  Introduction Learning objectives To make the student aware of dispersion phenomenon of air pollutants covering diffusion and advection, meteorological components, stability of atmosphere and corresponding plume shapes.  Meteorology depends greatly on the Earth's axis turn, which is responsible for air flow both in the northern and southern hemisphere.  Warm air rises at the solar-heated equator while cool air sinks to the poles due to equatorial heating and polar cooling.  Both horizontal and vertical motion in the atmosphere aid in understanding air pollution dispersion.  Measurements of meteorological parameters assist in the evaluation, modeling, and forecasting of air quality Department of Chemical Engineering, TIET November 22, 2024  Contd.. Role of atmosphere in source-sink relationship  Today, we will discuss about meteorological parameters and air pollution (meteorology of air pollution). Contd..  As you know, we have discussed like emissions sources, and its atmospheric transformations or formations of air pollutants, then their dispersion or diffusion their ultimate fate.  But as you know, even if the emissions are same, the concentrations of air pollutants in ambient air may be different at different places.  So, what is the difference? Basically the meteorological parameters govern all these emission sources, how much they will turn into air quality.  So, we will discuss about the impact of meteorology on air pollution means meteorological parameters and air pollution. How do they interact with each other? How these meteorological parameter  influence the air quality we will discuss around about the different places. metrological parameters roll into the air pollution, the fate of the air pollutants or decision of air pollution dispersion and the air pollution the total, the net worth of the air pollution in that sense. Contd..  Meteorology is the study of the atmosphere and the motions within it on short time scales (minutes to weeks).  Meteorology focuses on the atmospheric variables related to weather forecasting, at current or near-future conditions.  The manner air pollutants are dispersed and transported through the troposphere is determined by weather patterns (air quality forecasting, AQI). Contd..  Air movements influence the fate of air pollutants. So, any study of air pollution should include a study of the local weather patterns (meteorology).  If the air is calm and pollutants cannot disperse, then the concentration of the air pollutants will build up.  On the other hand, when strong, turbulent winds blow, pollutants disperse quickly, resulting in lower air pollutant concentrations. Contd.. Meteorological data helps:  Identify the sources of pollutants.  Predict air pollution events such as inversions and high-pollutant concentration days.  Simulate and predict air quality using computer models.  A brief history  The ancient Greeks contributed some of the earliest known observations and hypotheses on atmospheric phenomena, which led to the discovery of meteorology.  In 340, before Christian era (BCE), Aristotle produced Meteorological, the first summary on Schematic representation of the general circulation of atmospheric science atmosphere knowledge and usage of Earth’s orbit around the Sun. During this movement the Earth is rotated around an axis which has an angle of 23 ½ from its vertical axis The rotation axis is constant during the year. The result is that in June, when the northern hemisphere is turned towards the Sun, there is more direct light and longer duration of the day there. This results in warmer weather, compared to December when the northern hemisphere is turned away from the Sun Contd.. Hadley circulation  Scientists observed and created ideas on global atmospheric motion and regional scale meteorological phenomena in the 18th and 19th centuries.  In 1735, the planetary-scale George Hadley proposed a single cell circulation system in each hemisphere, with a low-pressure area around the equator and a high-pressure area around the Idealized general air circulation patterns, poles. drawn at the equinox. High-pressure zones are common around 300 latitude, producing clear skies and subsidence inversions  The air that moves along the surface of the Earth to close a Hadley cell is affected by Coriolis forces, causing it to curve toward the west if it is moving toward the equator or toward the east if it is moving toward the poles.  The resulting winds between roughly 30° and 60° are known as the westerlies,  and between the 30° and the equator they are the trade winds.  Near the equator, there is little wind since the air is mostly rising. That band is called the equatorial doldrums.  Similarly, the surface air is relatively calm around 30° latitude, forming a band called the horse latitudes. Contd..  The Earth is divided into six zones at different latitudes, the in the northern and three in the southern hemisphere which are:  0-300 Latitude, Hadley cell  30-600 Latitude, Ferrel cell  60-900 Latitude, Polar cell  The movement of air masses leads to the formation of zones of high pressure at latitudes 300 and 900 and, correspondingly, zones of low pressure at the Equator and at latitude 600  Based on the Coriolis effect (1835), the global circulation has three major Ideal temperature and surface pressure circulation cells in each hemisphere (Polar, distribution the rotation Earth with the three cell model Ferrell, and Hadley).  In 1904, established modern synoptic  The sun's rays heat the earth near the equator to a greater extent than at the poles. If the rotation of the earth were discounted, the heated air at the equator would rise, and cool air from the poles would move in to take its place. This would set up two theoretical cells, involving only longitudinal motion  However, the west-to-east rotation of the earth must be taken into account, since it has a profound effect on air currents, deflecting the winds to the right in the northern hemisphere and to the left in the southern hemisphere. The effect of the earth's rotation on wind velocity and direction is called the Coriolis force , and this  Thus, air movement on the global scale is not simply in longitudinal directions for the dual effect of heat differential between poles and equator and of the rotation of the earth along its axis establishes a more complicated pattern of air circulation.  The general global circulation pattern is composed of three cells of air movement in each hemisphere.  It is under this dual influence of thermal convection and the Coriolis force that high-and low-pressure areas, cold or warm fronts are formed.  One of the primary elements influencing air mass movement on this scale is the distribution of land and water masses over the surface of the earth. The great variance between conductive capacities of land and ocean masses accounts for the development of many of our weather systems. Over land masses, atmospheric temperature rises rapidly in the presence of solar radiation (day), then drops with equal rapidity in its absence (night), since landmasses quickly reradiate hear into the atmosphere. Conversely, air temperature over water rises and falls glory slowly, since heat energy received by water penetrates to deeper layers than het absorbed by land and is reradiated in lesser amount  At the equinox, the equator is directly under the sun, and the air there will be heated, become buoyant, and rise. As that air approaches the top of the troposphere (roughly 10 to 12 km), it begins to turn, some heading north and some south.  An eighteenth century meteorologist, George Hadley, postulated that the air would continue to the poles before descending. In actuality, it descends at a latitude of about 30° and then returns to the equator, forming what is known as a Hadley cell.  In similar fashion, though not as distinct, there are other cells, linked as in a chain, between 30° and 60° latitude, and between 60° and the poles. The descending air at 30° creates a persistent high-pressure zone with corresponding lack of clouds or rainfall that is a contributing factor to the creation of the world’s great deserts.  The deserts of southern California, the southwestern United States, the Sahara, the Chilean desert, the Kalahari in South Africa, and the great deserts in Australia, are all located at roughly 30° latitude for this reason.  Conversely, rising air near the equator and near 60° latitude tends to be moist after passing over oceans. As it cools, the moisture condenses, causing clouds Contd..  At the onset of World War II, the technological advances came to the forefront.  Radar development (1935), as well as increased upper-air surveillance from weather balloons and aviation.  In 1937, introduce the methods for analysing the upper-level atmospheric wave structures. Schematic representation of the general circulation of atmosphere Contd..  Based on earlier mathematical atmospheric modeling efforts, in 1950 produced the first computer which generate the weather forecasts.  Weather satellites (1960), Doppler radar (1990), and other technological innovations have continued to shape our understanding and forecasting of atmospheric processes.  What is atmosphere  Earth's atmosphere forms a very thin layer surrounding the globe.  95% of this air mass is within 20 km of the earth's surface.  This 20 km depth contains the air, we breathe as well as the pollutants we emit.  This layer, called the troposphere, is where we have our weather and air pollution  Vertical Division of the Atmosphere – Temperature Change The main characteristics of the troposphere are:  Continuous and uniform decrease of the temperature with height. The rate of temperature decrease is close to 6.50C/km.  The wind velocity increases with height since at the lower heights there is the effect of the Earth’s surface friction. The maximum velocity is observed at the upper layer of the troposphere.  Almost the whole quantity of water in all three phases (solid, liquid and vapor) occurs in the troposphere with the maximum concentration occurring at the lower layers.  The weather phenomena occur inside the troposphere. Atmosphere’s layers  Boundaries of the atmosphere  The lower boundary of the atmosphere has a perfectly well- defined but quite uneven, the surface of the land and the oceans.  Its upper boundary is not as well- defined, the atmosphere simply becomes thinner and thinner with increasing height until it is as thin as outer space Contd..  If the atmosphere were peeled off the earth and its edges stitched together, it would have an approximate thickness of 20 miles and a diameter of 16,000 miles.  This large width and small depth mean that most of the motions in the atmosphere must be horizontal.  they really play a significant role in the atmospheric motions or atmospheric dispersion of air pollutants and all other metrological parameters, transportation, temperature, humidity, etc.  Horizontal atmospheric motion  The horizontal movement of the atmosphere (e.g., winds) is driven mostly by uneven heating of the earth's surface.  The horizontal movement is also affected by the rotation of the earth (i.e., the Coriolis force) as well as the influence of the ground and the sea.  Equatorial heating and polar cooling  The average annual solar heat transfer to the earth's surface near the equator is 2.4 times that at the poles.  The atmosphere moves in response to this difference in heating, and in so doing transports heat from the tropics to the Poles.  Equatorial heating and polar cooling  Transports of heat primarily depends upon three processes:  Sensible heat flux: It is the process where heat energy is transferred from the Earth's surface to the atmosphere by conduction and convection.  This energy is then moved from the tropics to the poles by advection, creating atmospheric circulation.  Atmospheric circulation moves warm tropical air to the polar regions and cold air from the poles  A brief history  Based on the Coriolis effect (1835), the global circulation has three major circulation cells in each hemisphere (Polar, Ferrell, and Hadley).  In 1904, established modern synoptic meteorology (large-scale weather analysis taken at simultaneous time periods).  Equatorial heating and polar cooling  Latent heat flux: It moves energy globally when solid andliquid water is converted into vapor.  This vapor is often moved by atmospheric circulation vertically and horizontally to cooler locations where it is condensed as rain or is deposited as snow releasing the heat energy stored within it.  Equatorial heating and polar cooling Surface heat flux  The large quantities of radiation energy are transferred into the Earth's tropical oceans.  The energy enters these water bodies at the surface when absorbed radiation is converted into heat energy  Horizontal transfer of this heat energy from the equator to the poles is accomplished by ocean currents.  Equatorial heating and polar cooling Significance to air pollution  Air pollutants in the air circulate in the same way as air in the troposphere does.  Air movement is caused by solar radiation and the irregular shape of the earth and its surface which causes unequal absorption of heat by the earth's surface and atmosphere.  The effect of the earth's rotation  If the Earth did not rotate and remained stationary, the atmosphere would circulate between the poles (high pressure areas) and the equator (a low-pressure area) in a simple back-and-forth (backward and forward) pattern.  But because the Earth rotates, circulating air is deflected.  The effect of the earth's rotation  Earth rotates on its axis, circulating air is deflected toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere. This deflection is called the Coriolis effect  The Coriolis effect is responsible for many large-scale weather patterns on the earth. The effect of the earth's rotation Significance to air pollution Air movement around low-pressure fronts in the Northern Hemisphere is counter clockwise and vertical winds are upward, where condensation and precipitation take place.  The effect of the earth's rotation Significance to air pollution  High-pressure systems bring sunny and calm weather.  Anticyclones (high-pressure) are weather patterns of high stability, in which dispersion of pollutants is poor, and are often precursors to air pollution episodes.  The high-pressure area indicates a region of stable air, where pollutants build up and do not disperse.  Influence of the ground and the sea  Major mountain range like Himalayas is the major barrier to horizontal winds.  Different climates on one side than on the other side of the mountains.  Even smaller mountains and valleys can strongly influence wind direction.  Influence of the ground and the sea  The surface of the ground heats and cools rapidly from day to night and from summer to winter.  Solid ground is not mixed by the wind or convection currents, so heat cannot mix up and down.  So, solid surface temperature changes more rapidly than that of water bodies. Influence of the ground and the sea  The surface of oceans and lakes heats and cools slowly, mostly because their surface layers are mixed by the winds and by natural convection currents, thus mixing heat up and down.  Influence of the ground and the sea Example:  The summer sun warms the air above India more than the air over the surrounding oceans, which causes strong upward motion of the air over India.  Moist air from over the surrounding warm oceans flows inward to fill the low-pressure region caused by this rising air.  This moist air rises, cools, and forms the monsoon rains.  Vertical atmospheric motion  Vertical and horizontal motions in the atmosphere interact, the horizontal flows are driven by rising air at the equator and sinking air at the Poles.  In the atmosphere any parcel of air that is less dense than the air that surrounds, it will rise by buoyancy.  Vertical Atmospheric Motion  If any parcel denser than the surrounding air will sink by negative buoyancy.  Most vertical motions in the atmosphere are caused by changes in air density.  Air density change with temperature The density of any part of the atmosphere is given almost Air density change with temperature  Density is inversely proportional to temperature.  When temperature increases, with pressure constant, density decreases.  Air density change with temperature Example: Temperature inversion in atmosphere  A layer of cool air at the earth surface is overlain by a layer of warmer air. (Under normal conditions air temperature usually decreases with height.)  As a result, convection caused by air heating from below is limited to levels below the inversion  Diffusion of dust, smoke, and other air pollutants is likewise limited.  Air density change with temperature  Density is directly proportional to pressure.  As pressure increases, with constant temperature, density increases.  Thus, Air density will decrease by about 1% for a decrease of 10 hPa in pressure or 3 °C increase in temperature.  Meteorological parameters The main meteorological factors that affect dispersion are wind direction, wind speed and atmospheric turbulence (which is closely linked with the concept of stability).  Conclusion  Meteorology depends greatly on the Earth's axis turn, which is responsible for air flow both in the northern and southern hemisphere.  Warm air rises at the solar-heated equator while cool air sinks to the poles due to Equatorial Heating and Polar Cooling  Both horizontal and vertical motion in the atmosphere aid in understanding air pollution dispersion.  Measurements of meteorological parameters assist in the evaluation, modeling, and forecasting of air quality Department of Chemical Engineering, TIET November 22, 2024 Thank You Department of Chemical Engineering, TIET November 22, 2024