Urban Air Quality – a Signiﬁ Cant Threat to Human Health?

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 measurements are then converted into Air Quality

City authorities focus on e orts to reduce emissions and monitor levels of air pollutants.

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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

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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. cast, long-range transportation of pollution, to provide continuous data on wind Air pollutions are fi nally washed out chemical reactions and deposition. speed and direction at diff erent alti- of the sky by rain, fog or snow. Th is is tudes up to several kilometers. With an called “wet deposition”. When air pollu- What does Vaisala offer? optional acoustic system (Radio Acoustic tions deposit without the benefi t of rain, Th e major needs for atmospheric weather Sounding System, RASS), it can also it is called “dry deposition”. parameters for air quality forecasting measure the virtual temperature profi le include both surface and vertical profi le that can be used to determine stability How can air quality be measurements. Th e main parameters are conditions. Th e RF signal (intensity and estimated and forecast? wind speed and direction, turbulence, spectrum) can also be used to determine Air quality can today be forecast for a vertical wind and temperature profi les the mixing height as turbulent structure few days based on the weather forecast (to determine the layered atmospheric at the top of the mixed layer provides and a corresponding “chemical transport” air structure), visibility, cloud height and higher refl ectivity and a broader spec- model. Unfortunately the normal weather cover, rain, and solar radiation. trum for the RF signal. forecasts do not fully serve the needs of Vaisala can offer the latest tech- Measurements near the surface level air quality forecasting. Measuring and nology for the measurement of atmo- are also essential to estimate, for example, forecasting atmospheric conditions is spheric weather conditions relevant to mixing and transport of surface emis- critical for understanding the forma- the air quality estimation, dispersion and sions. Vaisala off ers a number of instru- tion, transformation, dispersion, trans- forecasting. Th e instruments include: ments to measure the principal weather port, and removal of the pollutants. More radiosondes, boundary layer profi lers, parameters, like wind, temperature, specifi c data on atmospheric conditions ceilometers, wind sensors and a number humidity, pressure and rain. All these is needed for better forecasts. One of the of surface weather sensors and stations. parameters are also packed into a single

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48 instrument, the Vaisala Weather Trans- 0 mitter WXT510, which offers a compact 40 1 2 solution for the purpose. In some areas, 4 32 visibility is used as an indicator for the 6 air quality. Vaisala has an optical visibility 9 24 12 DENAT_C sensor suitable for this purpose. 36 Ceilometers are designed 16 for the measurement of cloud 8 height and cover utilizing optical lidar technique (light detection and 0 ranging). These devices, however, have also turned out to be outstanding for air quality measurement purposes due to the principle of measure- 10 ment.Uni Theyt: measure optical scattering of aerosols and ice crystals to see the clouds. 20 As the performance and sensitivity has

increased 0over.00 the years, 30 they can also measure 1 .the00 low levels of pollutant aero- 2.00 sols - particulate matter. 4 0 This can be 4.00 used 6.00 to determine the real profile and 9.00 05/04/06 50 mixing height of theno aerosols.short descrip Thetion: NoVaisala full desc ription of a file 12.00Ceilometer CL31 has been successfully 36.00 used for this purpose to provide impor 60 - Loss in statistical life expectancy that can be attributed to the identified anthropogenic tant continuous data on the hour-to-hour contribution to PM2.5 (months), for the emissions of the year 2000. Calculation results for the and day-to-day variation of the aerosol 7meteorological0 conditions of 1997. Source IIASA. profile. In addition to supplying a variety 80 of instruments, Vaisala can also offer atmosphere can also be calculated from national meteorological institutes to

weather observation network solutions the vertical 90 temperature gradient. The improve their estimations, forecasts and services to support the needs for air dense network also includes five Vaisala and warnings on air quality for decision- quality monitoring and forecasting. ceilometers that100 measure the aerosol makers and the public. The most impor- Vaisala has built a dense observation profile and mixing height. The aim is tant users of air quality information are network in the Helsinki metropolitan to use this dense data11 0set for air quality the sensitive groups who can avoid bad . area in collaboration with the Finnish modeling to improve the real-time esti- outdoor air and take precautions in Meteorological Institute. Its goal is to mation and forecasting of12 0 spatial and advance. Good overall estimates of urban serve the purpose of air quality measure- temporal variations in air quality. air pollution - identification of sources, ment, among many other applications. effects on mixing, transformation and This Helsinki Testbed observation What to do with the transportation - help in making decisions network (http:\\testbed.fmi.fi) is based on air quality information to control air quality and implement a number of mast measurements using and forecasts? preventive actions to reduce emissions. Vaisala Weather Transmitters WXT510 Vaisala, as a weather observation equip- Everyday choices we make, about how at several altitudes. In addition to wind ment and solutions provider, can provide we get to work, how we heat our homes, profile information near the surface, real-time observation instruments and and what we consume, for example, all the vertical mixing conditions of the systems for air quality agencies and influence air quality in our region. n

Table 1. Candidate meteorological observing systems for dispersion applications

Dispersion variables Meteorological variables (not all required; algorithm dependent) Candidate measurement systems Transport Three-dimensional fields of wind speed and wind direction Profilers; Doppler weather radar; RAOBs; aircraft; tethersonde; Doppler lidar Diffusion Turbulence; wind speed variance;wind direction variance; stability; lapse 3D sonic anemometers; cup & vane anemometers; RAOBs; profilers; rate; mixing height; surface roughness RASS; scanning microwave radiometer (maybe); tethersonde Stability Temperature gradient; heat flux; cloud cover; insolation or net radiation Towers; ceilometers; profiler/RASS; RAOBs; aircraft; tethersonde; net radiometers; pyranometers; pyrgemeters Deposition, wet Precipitation rate; phase; size distripution Weather radar (polarimetric); cloud radar; profilers Deposition, dry Turbulence; surface roughness See turbulance Plume rise Wind speed; temperature profile; mixing height; stability Profilers/RASS; RAOBs; lidar; ceilometer; tethersonde; aircraft

RAOB – rawinsonde observation RASS – radio acoustic sounding system Source: Advances in meteorological instrumentation for air quality and emergency response, W. F. Dabberdt, G. L. Frederick, R. M. Hardesty, W.-C. Lee, and K. Underwood. Meteorology and Atmospheric Physics (2004).

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