Browsing by Subject "ilmanlaatu"

The aim of this thesis is to understand how restrictions and recommendations to limit the spread of Covid-19 pandemic affected air quality in Helsinki from January to September 2020 and examine the health benefits coming from the decreased pollutant levels. During that time many restrictions to people’s movements took place. This caused a decrease in traffic rates which in turn affected air quality. The air pollutants included in this study are nitrogen oxide (NOx), tropospheric ozone (O3) and particulate matter (PM2.5 and PM10). The data was uploaded from SMEAR III -station in Kumpula neighborhood and the results were obtained by comparing concentrations from 2020 to those of 2018-2019. The data were divided into three periods, which were studied separately. The first period was the time before the lockdown (1.1.-17.3.), 2nd period was during the lockdown (18.3.-15.6.), and the 3rd period was after the lockdown (16.6.-30.9.). In addition, the health effects caused by the changes in pollutant concentration were studied with a calculator for financial benefits of emission reductions made by Finnish Environment Institute. The change in NOx concentrations during 2020 compared to 2018-2019 were -36.4 % in 1st period, -26.5 % in 2nd period and +34.1 % in 3rd period. The changes for O3 were +4.8 % (1st period), -8.6 % (2nd period) and -11.6 % (3rd period). PM2.5 concentrations changed -39.4 % (2nd period) and 0.0 % (3rd period) and PM10 concentrations -46.9 % (2nd period) and -14.7 % (3rd period) during 2020 compared to 2018-2019. Decrease of NOx in 1st period caused 2 600 t€/y savings in costs of air pollution related health effects. The changes in PM2.5 and NOx generated savings of 38 000 t€/y during 2nd period and -2 400 t€/y during 3rd period. Even though the pollutant concentrations decreased in most periods, the decrease can’t be explained only by changes in traffic rates and human activities. Other factors contribute air pollutant levels as well, including atypical weather during 2020. The study could be continued by separating the effects of weather, traffic and other contributing factors in changes in air pollutant concentrations.

Due to population growth, urbanization, and increase in life expectancy, the urban population is growing, and by 2050 68% of the global population is expected to live in urban areas. Even though the air quality in urban settings has greatly improved in recent decades due to increased legislation, restriction, and monitoring, the negative health impacts associated with pollutants have not completely diminished. Air quality varies on a local scale due to urban form and function, that creates differences in experienced exposure among individuals. These exposure differences among socio-economic groups have been studied, but no clear consensus has been found, as the results have been very diverse and even contradictory. Therefore, conducting local level studies is important in order to identify local patterns of exposure and to recognize them in urban planning. However, previous literature on the topic in Finnish context is lacking. This thesis studies interpolated air pollutant exposure among one susceptible socio-economic group – the elderly – and aims to identify possible hotspots of both in Helsinki, Finland. The distribution of the elderly and air quality is assessed through Moran’s I calculations. Global Moran’s I is used to assess for spatial autocorrelation, and local Moran’s I is applied to identify local clusters. To further examine the relationship, correlation coefficients are calculated through Spearman’s rank correlation coefficient. According to the results, there is a weak positive correlation between the elderly and air quality, indicating that generally air quality tends to be worse when the number of elderly people increase. However, the relationship is stronger among younger age groups, although the differences between age groups is very small. The exposure was also assessed through overlapping high value clusters, which indicate that elderly clusters in the city center are located in areas with low air quality, while elderly clusters in Lauttasaari and Vuosaari are located in areas with good air quality. Previous studies regarding the relationship between age and air pollution exposure have been contradicting in different cities, and therefore these results provide important knowledge about the problem specifically in the context of Helsinki. Additionally, the results are be observed in the light of the larger discourse around socio-economic status and air pollution, but further studies on the topic are still needed. Including multiple socio-economic variables and the dimension of negative health outcomes would aid in identifying 1) the most important socio-economic factors in the context of negative health outcomes associated with air pollution, and 2) those areas where multiple important socio-economic factors and low air quality are overlapping and therefore might have higher risk for negative health outcomes.

Air pollution is the most severe environmental problem in the world in terms of human health. The World Health Organisation (WHO) estimates that 91% of the world's population is exposed to high air pollutant levels. The risks are particularly high in urban areas, where often high population densities are combined with high air pollutant levels. Urban street canyons are especially prone to high pollutant levels due to the proximity of traffic and reduced exchange of air with the street canyon and air above, referred to as ventilation. As a result, one of the most important topics in city planning is how to avoid designs that impact the air quality negatively. Street trees are often planted in street canyons for aesthetic purposes while they can also improve thermal comfort. The air quality within street canyons is affected by street trees in two ways. They provide leaf surface for air pollutants to deposit on, thus cleaning the air. On the other hand, they block the airflow within the street canyon, thus decreasing the ventilation of air pollutants. In previous studies the latter effect has generally been found stronger. However, due to the various benefits of street trees, leaving them completely out from street canyon designs is rarely an option. The City of Helsinki is planning to develop its current inbound motorways into city boulevards which has raised concerns towards the local air quality levels due to high projected traffic rates. The aim of this study was to find which of five street-tree scenarios, realistic for the city boulevards, is the best in terms of air quality. Pedestrian-level aerosol mass concentrations were used as the measure of air quality. Furthermore the impacts of vegetation and dependency of aerosol mass concentrations on various flow statistics were studied in order to explain the differences between the scenarios. Large-eddy simulation (LES) model PALM was utilised to study the flow field above and within a city boulevard and to model the dispersion of traffic-related aerosols. Aerosol particles of different sizes were represented using a sectional aerosol model SALSA. The suitability of the used LES setup for such intercomparison studies was also investigated. The results showed that the street trees have generally a considerable negative impact (-2% to 54%) on pedestrian-level aerosol mass concentrations. Trees were find to reduce the mean wind speeds within the street canyon, which correlated strongly with the pedestrian-level concentrations. This was particular with a parallel wind direction to the street canyon due to decreased ventilation. Turbulence produced by the street trees was partially able to compensate for the reduced ventilation in some scenarios. The increased turbulence could be observed up to heights exceeding the maximum building height. Based on the results, it is recommended to prefer variable-height street-tree canopies over uniform ones within street canyons similar to the studied one. Uneven canopy increases turbulence and related pollutant transport which partially compensates decreased ventilation due to decreased wind speeds. It is also recommendable to consider minimising the ratio of the total crown volume to the street canyon volume, as ventilation decreases sharply as the ratio increases.

Työssä tutkitaan ilmanlaatuun liittyvän julkisen huomion kehitystä Kiinan kansantasavallassa vuosina 2000–2018. Teoreettisena viitekehyksenä käytetään Jens Newigin vuonna 2004 esittelemää teoriaa julkisen huomion voimistumisesta ja vaimenemisesta sekä näihin vaikuttavista tekijöistä. Julkista huomiota tutkitaan käyttämällä seitsemän eri kiinankielisen sanomalehden CCND-tietokannasta löytyvää levikkiä vuosilta 2000–2018. Tietokannasta tehdään hakuja käyttämällä ilmanlaatuun liittyviä hakusanoja ja tulokset esitetään tilastollisessa muodossa. Tämän lisäksi kirjallisuuskatsauksen avulla tunnistetaan lainsäädännöllisiä, luonnontieteellisiä ja yhteiskunnallisia tekijöitä, joilla on oletettavasti ollut vaikutus ilmanlaadun saamaan julkiseen huomioon. Lopuksi tulokset kootaan yhteen huomiosykleiksi ja etsitään muuttujien välisiä riippuvuussuhteita huomiosyklien pohjalta. Tutkimuksen tuloksista käy ilmi, että mittauksin havaittu ilmanlaatu ei korreloi suoraan julkisen huomion kanssa. Keskimääräinen ilmanlaatu on parantunut Kiinan kansantasavallassa tutkimuksen ajanjaksolla, mutta ilmanlaadun saama huomio on samaan aikaan lisääntynyt. Ilmanlaadun ongelmien havaittavuudella ja paremman ilmanlaadun odotuksilla todettiin olevan merkittävin korrelaatio julkisen huomion kanssa. Myös voimistuneen julkisen huomion ja ilmanlaatuun vaikuttavien poliittisten toimenpiteiden välinen riippuvuussuhde oli havaittavissa. Tutkimuksen tulokset eivät suurimmaksi osaksi vastaa teoriaan kuuluvia hypoteeseja. Työn lopussa ehdotetaan teoriaan muutamia tarkennuksia, joilla sen käyttökelpoisuutta Kiinan kansantasavallan kontekstissa voisi mahdollisesti parantaa.

Kaupungistuminen on nopea ilmiö maailmanlaajuisesti. Kaupungistuminen johtaa myös muutoksiin maankäytössä, mikä usein näkyy kaupunkien tiivistymisenä viherrakenteen kustannuksella. Viherrakenteen ilmalaatuun liittyvistä vaikutuksista on tehty paljon tutkimusta, mutta tutkimuksien tulokset aiheesta ovat ristiriitaisia. Maisterintutkielma käsittelee viherrakenteen vaikutuksia ilmanlaatuun kaupungeissa. Työ pyrkii kartoittamaan mitkä taustalla olevat tekijät vaikuttavat viherrakenteen ilmanlaadullisiin seurauksiin. Lisäksi työ tarkastelee voiko tuloksia soveltaa suomalaiseen kaupunkisuunnitteluun ja jos voi niin millä tavoin. Tutkielma suoritetaan käyttäen systemaattista kirjallisuuskatsausta, joka tiivistää ja arvioi jo valmiina olevaa tutkimusaineistoa sekä kartoittaa epävarmuusalueita. Kokoavan tutkimuksen avulla voidaan selvittää ovatko tutkimusten tulokset esimerkiksi yhteneviä sen osalta, että viherrakennetta kannattaa integroida kaupunkeihin ilmaa puhdistavan vaikutuksen takia Tutkielman aineistona toimii hakulausein sekä sisäänotto- ja poissulkukriteerein huolellisesti ja kriittisesti valitut tieteelliset tutkimukset. Tutkielmaan valikoitui 51 alkuperäistutkimusta. Aineiston analyysissä käytettiin sisällönanalyysiä, joka tarjoaa mahdollisuuden tarkastella asioiden välisiä yhteyksiä, yhtäläisyyksiä ja eroavaisuuksia. Valikoidut tutkimukset koottiin tiivistetysti taulukkoon tutkimuksen läpinäkyvyyden lisäämiseksi. Aineiston sisällönanalyysin perusteella käy ilmi, että viherrakenteen vaikutus kaupunkien ilmanlaatuun on pääosin positiivinen. Neljännes tutkimuksista viittaa siihen, että sillä voi olla myös ilmanlaatua heikentäviä vaikutuksia. Erityisesti viherseinillä ja -katoilla havaitaan eniten ilmanlaatua parantavia ominaisuuksia. Toiseksi tulevat puut, pensaat ja nurmi, ja kolmanneksi suuremmat viheralueet kuten metsät ja puistot. Viherseinät ja -katot aiheuttavat vähiten haitallisia vaikutuksia, kun taas suurimmat haitat liittyvät puihin, pensaisiin ja nurmikkoon. Tulosten vaihtelevuus johtuu erilaisista tutkimusmenetelmistä, tutkimusajankohdista, ilmastollisista olosuhteista, vuodenaikojen vaihtelusta, ilmansaastepitoisuuksista alueella, vuorokaudenajoista, kasvuston sijainnista, viherrakennetyypistä sekä kasvilajeista. Tulosten soveltaminen suomalaiseen viherrakentamiseen on haastavaa, sillä tutkimusten ilmasto-olosuhteet eroavat merkittävästi Suomen oloista. Samankaltaisiin suomalaisiin olosuhteisiin valikoitujen tutkimusten mukaan viherkattojen ja puistojen suosiminen kaupunkirakenteessa, metsien säilyttäminen vilkkaampien teiden varrella ja viherseinien hyödyntäminen katujen varsilla voivat osittain parantaa ilmanlaatua.