Atmosphere and Air Pollution

Module 1: Introduction to Atmosphere and Air Pollution

• Outlines four spheres of the Earth, an overview of the Earth's atmosphere, the thickness of the Earth's atmosphere, and its vertical structure.
• Covers temperature, pressure, atmospheric layers, the definition of air pollution, and air pollution systems.
• Discusses the philosophy of air pollution control, the classification of air pollutants and their sources.
• Mentions components of air pollution systems or air quality management and ends with the challenges of managing air pollution systems.

Four Spheres of Earth

• Earth's systems consists of four spheres: Lithosphere, Hydrosphere, Atmosphere, and Biosphere
• Lithosphere: encompasses the Earth's cold, hard, solid crust (surface), semi-solid land beneath the crust, and liquid land near the planet's center.
• Hydrosphere: contains all the solid, liquid, and gaseous water of the planet and ranges from 10 to 20 kilometers in thickness.
• Atmosphere: contains all the air in Earth's system and extends less than 1 m below the planet's surface to more than 10,000 km above it.
• Biosphere: Earth's "life zone," including living organisms (including humans) and undecomposed organic matter.

Overview of Earth's Atmosphere

• The layers of the atmosphere are: Thermosphere, Mesosphere, Stratosphere, and Troposphere

Thickness of Earth's Atmosphere

• Relative to Earth's size, the atmosphere is extremely thin
• Earth's atmosphere has 90% of its mass below 16 km
• Given Earth's diameter of 12,756 km, the atmosphere's thickness is comparable to the skin of an apple
• Earth's atmosphere is a layer of gases (air) held by Earth's gravity.
• The atmosphere creates pressure, absorbs meteoroids and ultraviolet solar radiation, warms the surface through heat retention (greenhouse effect), and reduces temperature extremes between day and night (diurnal temperature variation), thus maintaining conditions for life and liquid water.

Layers of Atmosphere

• Temperature increases to as high as 2000°C in the Thermosphere.
• Even though temperatures can reach 2000°C, the atmosphere is very thin because each two molecules of gas are ~1 km apart
• The thermosphere includes the ionosphere, which creates auroras and is important for radio waves.
• The Mesosphere is much thinner than other layers
• The temperature does decrease with altitude at 2°C/km in this layer
• Gases in the Stratosphere make up approximately 19% of Earth's gases, but contains nearly no water vapor
• Contains the Ozone Layer
• The Stratosphere increases in temperature with altitude by 1°C/km
• 80% of atmospheric mass is found in the Troposphere
• The Troposphere temperature decreases with altitude 6°C/km and all weather of the Earth occurs in the Troposphere

Vertical Structure of the Atmosphere

• Gravity holds the atmosphere to the Earth.
• Consequently, the pressure is defined by the weight of a vertical column of air over the area.

Vertical Profiles of Temperature

• Temperature declines in the troposphere due to decreases in pressure, causing a decrease in average kinetic energy.
• Molecules of air move slower and cause the temperature to decline
• This can be predicted mathematically
• In the Stratosphere, increasing temperature is caused by ozone absorption of UV radiation.
• Decreasing temperature in the mesosphere is caused by decreasing ozone.
• The thermosphere warms due to the absorption of UV radiation by O2.
• The Troposphere is from 0 to 15 km, the lowest area of the atmosphere where life and weather exist
• In the troposphere temperature decreases with altitude
• Long-wave radiation emitted from Earth is absorbed by the atmosphere; as the atmosphere becomes less dense with increasing altitude there is less air to absorb it
• The top of the troposphere is the tropopause.

Stratosphere

• Is approximately 15 to 50 km altitude
• The temperature increases with altitude
• It heats up because ozone (O3) absorbs ultraviolet radiation from the Sun.
• The top of the stratosphere is the stratopause.
• Altitude in the Mesosphere is from 50 to 90 km
• Temperature decreases with altitude in the mesosphere
• The Mesopause during summer at high latitudes is found to have the lowest temperatures in the entire atmosphere (130 K or -226°F)
• The top of the mesosphere is the mesopause.

Thermosphere

• 90 to 500 km altitude.
• Temperature increases with altitude above 90 km, and is constant above 200 km.
• Heating occurs due to absorption of solar radiation (wavelengths less than 0.2 microns) by molecular oxygen (O2).
• The highest temperatures in the atmosphere can be found in the thermosphere, 2000 K can occur.

Air Pollution Definition

• Air pollution is the presence of any substances (solid, liquid, or gas) in the atmosphere at "such a concentration" that may be injurious to humans, animals, plants, property, or the atmosphere itself.
• Air pollution requires a clean atmosphere and an addition of an external addition to create effects.

Systems of Air Pollution

• Systems of air pollution include sources of emissions, atmospheric processes and receptors, or air concentrations
• Anthropogenic (point, area, mobile) or biogenic emissions are deposited for loading
• Chemistry(gaseous & aqueous & heterogeneous), micro-physics, and wet & dry deposition, help transport emissions
• Wind, ABL, and cloud transformation help transport emissions in air
• Systems of Air Pollution flow from a Source of emissions to Transport and transformation to Human exposure to Health effects
• Air quality researchers, IT developers, and Meteorologists all contribute to a Science and Modelling system that contributes to Policy Makers and other environmental safety groups
• Systems includes: air quality researches, meteorologists, health researchers, social scientists, IT developers, science & modeling system, cloud service platform, data analysis system, cloud infrastructure, data hub and services, HPC cluster, policy makers, NGO's city environment department, industry, doctors and urban planners

Philosophy of Air Pollution Control

• The goal is to reduce pollutant emissions to a point where noticeable adverse effects associated with the pollutants do not exist.
• The extent of reduction is determined by links between sources and receptors (using meteorology) and by setting safe air quality levels for receptors.
• Air Quality Standards protect receptors through Primary Health Standards, Secondary Standards for vegetation/crops, and Sensitive area standards.

Challenges of Managing Air Pollution System

• Managing the challenge must include problem solving the 3 dimensions
• Must deal with transport outside of contro/regulation
• Impacts must be instant and chronic
• Receptors remediation is nearly impossible
• A solution cannot be delayed
• Types of Readiation include: Medium, Source and Receptor remediation

Two Basic Categories of Air Pollutants

• Criteria Pollutants: PM, SO2, NOx, and CO
• No-Criteria Pollutants: Pb, Asbestos, Vinyl chloride, Mercury, Arsenic, TOC(Trace Organic Carbon) and others
• To best develop the basis of determining Criteria, we must look at the: Dose-Response/Cause - Effect Knowledge (receptor specific)

Criteria Pollutants

• Criteria air pollutants are those that have been regulated, continuously monitored, and are used as indicators of air quality.
• The Clean Air Act (CAA) of 1970 identified six common air pollutants of concern, called criteria pollutants.
• The criteria pollutants are: Carbon monoxide (CO), Nitrogen dioxide (NO2), Sulfur dioxide (SO₂), Ozone (O3), Lead (Pb), and Particulate matter.
• Photochemical oxidants form secondary air pollutants under the influence of sunlight, with complex photochemical reactions in air containing nitrogen oxides and reactive hydrocarbons as precursors.
• The most adverse components formed by photochemical reactions in polluted air are ozone (O3) and peroxyacetyl nitrate (PAN), plus aldehydes, ketones, organic and inorganic acids, nitrates, sulfates, etc.
• Ozone makes up about 90% of the total photochemical oxidant pool.
• Other photochemical oxidants of concern in the atmosphere are: Nascent oxygen [O], Excited molecular oxygen (O2), Peroxy-acetyl nitrate(PAN), Peroxy-propinol nitrate(PPN), Peroxy-butyl nitrate(PBN), Nitrogen dioxide (NO₂), Hydrogen peroxide (H2O2) and Alkyl nitrates.

Hazardous Air Pollutants (HAPs)

• Hazardous air pollutants, also known as toxic air pollutants or air toxics, are pollutants that can cause cancer or other serious health effects, reproductive effects or birth defects, or cause adverse environmental and ecological effects.
• USEPA has identified 187 chemicals a HAPs by the Clear Air Act of 1990
• HAPs are more toxic than criteria pollutants; "...may reasonably be expected to result in serious irreversible... disease, including cancer”
• The thirty-three are commonly found in the urban area
• Examples include: Benzene, Perchiorethlyene and Methylene chloride
• HAPS may originate from mobile or stationary sources

Classification of Pollutants

• All air pollutants may be classified according to origin, chemical composition, and state of matter.

Based on Origin:

• Primary pollutants are emitted directly to the atmosphere and found there in their emitted form, such as sulfur dioxide (SO2), nitric oxide (NO), carbon monoxide (CO), and hydrocarbons (HC).
• Secondary pollutants form in the atmosphere due to reactions, for example particulate matter (PM), sulfuric acid (H2SO4), Ozone (O3), and peroxy-acetyl nitrate (PAN).
• Some pollutants may be both primary and secondary: that is, they may be both emitted directly and formed from other primary pollutants i.e., PM, NOx.

Based on Chemical Composition

• Organic compounds contain mainly carbon and hydrogen, but can contain elements such as oxygen, nitrogen, phosphorus, and sulfur. Examples are hydrocarbons, aldehydes, ketones, carboxylic acids, alcohols, amines, and organic sulfur compounds etc.
• Inorganic materials in contaminated atmosphere include CO, CO2, carbonates, SOX, NOx, O3, hydrogen chloride (HCI) and hydrogen fluoride (HF) etc

Based on State of matter:

• Particles may be finely divided solids and liquids, including dust, fumes, smoke, fly ash mist, and spray.
• Under proper conditions, particulate pollutants will settle out of the atmosphere under gravity.
• Gaseous pollutants are formless fluids that completely occupy the space into which they are released, behaving much as air, and do not settle out of the atmosphere e.g.- CO, CO2, SOX, NOx, and hydrocarbons (HC).
• Some pollutants, like polycyclic aromatic hydrocarbons (PAHs), can be emitted as both gaseous and particulate matter, based on their molecular weight, shape, and vapor pressure.

Components of an Air Pollution System (Air Quality Management)

• The Components of an Air Pollution system may include: emissions, measurement and modelling of pollution, control options, cost/benefit analysis and exposure analysis.

AIR QUALITY MANAGEMENT CYCLE

• Consists of a system of: Establish goals, Determine Emission reductions, Scientific Research, Implement Programs, Develop Control Strategies, Undertake ongoing evaluation
• Components consist of cycles of emissions, exposure assessment, dispersion modeling, and economic assessment
• Systems includes assessment cycles on both boundary of Effects, valuations of damages and social, effects on economy and output effect