Urban Air Quality – a Signifi Cant Threat to Human Health?
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Hannu Talvitie Research Manager Vaisala Helsinki, Finland Urban air quality – A signifi cant threat to human health? Urban air pollution poses a signifi cant the risks that air pollution poses to their diseases. According to the World Bank, threat to human health, the environment citizens. every year an estimated 800,000 people and the quality of life of millions of people On the other hand, such countries die prematurely from lung cancer, in some of the world’s largest cities. (e.g., still face the problem of polluted air even cardiovascular and respiratory diseases New Delhi, Hong Kong, Beijing, Jakarta, though air quality has been improving caused by outdoor air pollution. In Hong Los Angeles and Mexico City). Urbaniza- gradually over the last two decades. For Kong, for example, it is estimated that tion and the associated growth in indus- example, many large cities in Europe still by improving the air quality from the trialization and traffi c have resulted in exceed the specifi c air quality standards existing “average” level to “good” level, the increase of air pollution in densely for ambient pollutants. Th e Helsinki 64,000 hospital days would be saved. populated areas, causing deterioration metropolitan area in Finland, for example, Th ese severe health eff ects are the in air quality. Many cities will need to is one of the cleanest cities in Europe but reason that most countries have already take action to enhance their institutional still the daily limits are exceeded every taken preventative measures to limit and technical capabilities to monitor year. emissions and set limits (called standards) and control air quality and implement for urban air pollutants. City authorities preventive actions in order to reduce How can air pollutants focus on eff orts to reduce emissions and affect human health? monitor levels of air pollutants. A number of epidemiological studies have shown that ambient air pollutants, espe- What are the main cially fi ne and ultra fi ne particulates, pollutants in urban air? have an adverse eff ect on human Scientists have defi ned the main air health. Th is is due to the fact pollutants that pose a health risk for that these tiny particulates humans in urban areas. Th ese pollutants can penetrate deep into are: inhalable particulates (PM10) and the lungs and even be fi ne particulates (PM2.5), nitrogen oxides dissolved in the blood. (NOx), sulphur dioxide (SO₂), ozone (O₃), Th e health eff ects can be carbon monoxide (CO), and lead (Pd). especially hazardous for For each of these pollutants, the World sensitive groups, like Health Organization has defi ned air children, senior citi- quality guidelines for protection against zens, and people with harmful health eff ects. Th e guidelines asthma, obstructive defi ne the specifi c limits or concentra- lung disease (chronic tions that should not be exceeded. Coun- obstructive pulmo- tries often have their own standards that nary disease are similar but the specifi c levels can vary - COPD), and slightly. cardiovascular To measure air quality, networks of monitors record the concentrations of the major pollutants at more than 3,000 locations in the world each day, mostly in developed countries. Th ese raw measure- ments are then converted into Air Quality City authorities focus on e orts to reduce emissions and monitor levels of air pollutants. 4 | Vaisala News 174 / 2 0 07 800 1000 700 900 600 800 700 500 600 400 500 300 400 Altitude (meters) 200 300 200 100 100 0 00 06 12 18 24 Figure 1. Th is picture shows a 1-day measurement of aerosol profi le using the Vaisala Ceilometer CL31 on Nov 22, 2005, in the Helsinki area, Finland. During this day there was a strong inversion that lasted almost the whole day. A high concentration of low level aerosols (particulates from traffi c) can be seen below 100 m, increasing rapidly after 7:30 in the morning. Index (AQI) values. Th e AQI has been to remove it in energy production are that are diff erent from those formed in developed to make it easier for people available and already in common use in burning processes. to understand the signifi cance of moni- most developed countries. (Note: carbon tored and forecast air pollution levels. It dioxide is not counted as a pollutant but How does weather focuses on health eff ects that can take the main greenhouse gas.) affect air quality? place within a few hours or days after Pollution from traffic consists of Changes in day-to-day weather are the breathing polluted air. particulate matter, NOx, CO, volatile greatest factor in controlling the changes An AQI value is calculated for each organic compounds (VOCs), and also in air quality. Weather determines how of the individual pollutants in an area other compounds in small amounts, quickly pollutants are dispersed away (ground-level particulate matter, carbon like polyaromatic hydrocarbons (PAH). from an area and also the thickness of monoxide, sulfur dioxide, nitrogen Lead emission from traffi c has reduced the atmospheric layer (called the mixing dioxide, and ozone). Th e pollutant with dramatically after moving to unleaded height) where the emissions are diluted the highest AQI is used as the overall AQI fuels. Particulates come from the exhaust in a vertical direction. Normally, pollut- reading for that day and is listed as the emissions, especially from diesel engines, ants are mixed with the help of convec- principal pollutant. but also from dust and dirt from roads tion or blown away by wind from their Various agencies around the world and tires. Other fi ne particulates are sources without building up to unsafe measure such indices, though defi ni- formed by chemical reactions in the amounts. But the pollutants can also be tions may vary. Th e index is defi ned so atmosphere. Formation of ozone (O₃) in trapped close to the surface. Th ey cannot that it gives a value of 100 at the specifi c urban areas is mainly caused by traffi c escape, and after a while they may build value of each pollutant. Th e United States pollutants in a photochemical reaction up to unhealthy levels. Th is trapping can Environmental Protection Agency (EPA) with UV radiation from the sun. happen when winds are weak or calm, has determined the AQI scale and health Some of the pollutants also come and when the air close to the ground cools classifi cation as: from natural sources. For example, forest down and warm air moves over, creating fi res emit particulates and VOCs into the a stable condition that keeps pollutants 301 – 500 Hazardous Maroon atmosphere. Volcanoes spew out sulfur close to the surface. Th ese so-called inver- dioxide and large amounts of volcanic sions frequently occur on clear nights. 201 – 300 Very unhealthy Purple ash. Sand storms can also mix particu- Poor air quality can also result from 151 – 200 Unhealthy Red lates into the air from the underlying summer heat. In hot, sunny weather 101 – 150 Unhealthy for sensitive groups Orange ground surface. Vegetation emits VOCs photochemical smog can form 51 – 100 Moderate Yellow 0 – 50 Good Green Particulate Matter (PM) can be divided into four size classes: 1. Large particulates are over 10 microns (>10 µm) in diameter. What are the main 2. PM10 — Particulates under 10 microns (0 – 10 µm) can be inhaled below sources of emission? the nasopharynx area (nose and mouth) and are thus called inhalable Most air pollution comes from human particulates (PM10). activities: burning either fossil fuels (coal, 3. PM2.5 — Particulates that are under 2.5 microns (0 – 2.5 µm) are called oil or natural gas) to power motor vehi- fi ne particulates (PM2.5) and they travel down below the tracheobron- cles and industrial processes, or burning chial region (into the lungs). of biomass to heat houses or produce 4. UFP — Th e smallest particulates are under 0.1 microns (0 – 0.1 µm) and energy. Th e burning processes release are called ultra fi ne particulates (UFP). Th ey can travel in the deepest particulate matter, carbon monoxide, parts of lungs and be dissolved into blood. carbon dioxide (CO₂) and partially burnt hydrocarbon compounds into the atmo- Th e most hazardous size classes to humans are PM2.5 and UFP as they pene- sphere. Depending on the origin of the fuel, trate into the lungs and can even be dissolved into the blood. SO₂ concentrations released in combus- tion vary considerably. Technologies 174 / 2007 Vaisala News | 5 Altitude (Meters) 400 300 200 100 Warmer air Inversion layer Cooler air 0 –20°C 0°C +20°C Temperature through complex chemical reactions tasks is to get more dense and accurate Vaisala radiosondes off er the highest involving NOx, O₃ and VOCs. Photochem- observation data on the mixing height level of temperature, humidity and wind ical smog has a light brown color and can across urban areas to better determine measurement performance for synoptic reduce visibility and aff ect breathing. the air volume where the surface pollut- soundings all over the world. Th ere are Wind can also transport pollution ants are mixed. also special sensor options to measure over long distances. For example, in the Modern air quality models can take ozone and radioactivity profi les in the Helsinki metropolitan area, more than half a variety of data as input: inventory and atmosphere. of the fi ne particulates (PM2.5) are trans- models of emission sources, local disper- Vaisala’s boundary layer profi ler uses ported from outside the country, mainly sion and mixing, weather model and fore- radio frequency (RF) Doppler technique from Central and Eastern Europe.