Air quality index

Summary

An air quality index (AQI) is an indicator developed by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. As air pollution levels rise, so does the AQI, along with the associated public health risk. Children, the elderly, and individuals with respiratory or cardiovascular problems are typically the first groups affected by poor air quality. When the AQI is high, governmental bodies generally encourage people to reduce physical activity outdoors, or even avoid going out altogether. When wildfires result in a high AQI, the use of masks such as N95 respirators outdoors and air purifiers incorporating HEPA filters indoors are also encouraged. Different countries have their own air quality indices, corresponding to different national air quality standards. Some of these are Canada's Air Quality Health Index, Malaysia's Air Pollution Index, and Singapore's Pollutant Standards Index. Overview Computatio

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Improvement of an urban turbulence parametrization for meteorological operational forecast and air quality modeling

Clive Muller

During the last century, urban pollution has increased with the growth of cities. Urban air quality has become a high priority as it is directly linked to concerns such as human exposure and health. The present work is dedicated to urban air quality modeling with focus on urban meteorology. The main goal is to improve meteorological and air quality simulations in urban areas. Based on measurements and numerical air quality simulations, Chapter 3 describes the meteorological situation and tests an emission inventory for an ozone pollution episode in Mexico City (2 March 1997), in order to determine the principal factors to be accounted in an air quality study. The Mexico City case shows the great influence of meteorological conditions and pollutant emissions on air quality. A thorough understanding of the phenomena governing the meteorological conditions, like small scale convergence, and an accurate emission inventory validated by VOC measurements in the city, are sensitive elements in an air quality study. In Chapter 4, the presence of an Urban Heat Island (UHI) is underlined over the city of Basel (Switzerland) with the BUBBLE measurements. Further on, the ability of aLMo (the operational weather prediction model of MeteoSwiss) to reproduce the effect of a city on the boundary layer atmospheric flow fields is investigated. Results show that aLMo is not able to reproduce the UHI and hence that its surface scheme based on the Monin-Obukhov Similarity Theory (MOST) is not adapted for the urban areas. Therefore, the Buildings Effects Parametrization (BEP) which has been developed by Martilli et al.(2002) especially for urban areas, is implemented in aLMo. Results show that alMo is now able to reproduce the main behavior of the urban boundary layer as the UHI and BEP has hence a real enhancement potential for aLMo. Chapter 5 shows the sensitivity of aLMo with respect to its vertical resolution. In order to limit the sensitivity of aLMo to the grid resolution, BEP is modified. The mesoscale model furnishes the upper boundary conditions for the inner calculation of BEP. That is, BEP recalculates independently the vertical profiles of wind, temperature and energy based on the surface fluxes of momentum, heat and turbulent kinetic energy. The results obtained show a decrease in the sensitivity to the resolution and a better agreement with the measurements. Furthermore, the modified version of BEP gives additional meteorological fields (temperature, wind and TKE) in the urban canopy. The computed temperature in the urban canopy shows a good agreement with measurements in a Basel street canyon. This work shows that it is not necessary to have a high resolution for taking into account modification of the atmospheric flow fields induced by a city.

EPFL2007

Growing population, extensive use (and abuse) of the natural resources, increasing pollutants emissions in the atmosphere: these are a few obstacles (and not the least) one has to face with nowadays to ensure the sustainability of our planet in general, and of the air quality in particular. In the case of air pollution, the processes that govern the transport and the chemical transformation of pollutants are highly complex and non-linear. The use of numerical models for simulating meteorological fields, which in turn will determine the transport of pollutants in the atmosphere, is thus a very appropriate tool to describe and understand the air pollution problematic. This work focuses on the meteorological simulation, using a mesoscale model. The stress is particularly put on the parameterisation of urban induced effects on the meteorological fields above a city. A detailed urban parameterisation scheme has been implemented in a mesoscale model in a previous work. This new scheme takes into account the presence of a city in a more accurate way as the traditional method usually used in mesoscale models. In the first part of this work, the urban module was validated for a one-dimensional off-line simulation within and above a street canyon in the city of Basel/Switzerland. The simulation results were compared with measurements taken within and above the same street canyon during an intensive observation period in the frame of the BUBBLE project (Basel UrBan Boundary Layer Experiment). The comparison with the measurements and with a simulation using the traditional urban parameterisation showed that the detailed urban scheme improved the quality of the simulation of turbulent fluxes and meteorological parameters (wind, temperature) in the urban canopy. Further on, the mesoscale was applied for a three-dimensional simulation over the city of Basel and its surroundings. The results showed that the model is able to reproduce the wind pattern that prevailed during the simulated episode, and that the accuracy of the temperature simulation in the city is improved with the urban module. In the third part of this work, an air quality study was performed over the Mexico City basin. The mesoscale model simulated the meteorological conditions for the chosen episode (1 and 2 March 1997). The results were then passed to TAPOM, a Eulerian photochemical model that calculates the space and time distribution of air pollutants. The simulated concentrations over the basin showed good agreement with the observed values. The validated model could then be used to test some emissions reduction scenarios for Mexico City. The use of the detailed urban parameterisation scheme for meteorological fields and air pollutants concentration simulation improved the quality of the results in almost all the applied situations. Consequently, the full modelling tool presented and validated in this work can be used for air quality modelling studies over cities and their surroundings.

EPFL2004

Understanding the origins and fate of air pollution in Bogota, Colombia

Erika Maria Zarate Torres

Bogota has more than 8 million inhabitants and is the 5th biggest urban agglomeration in Latin America. It has more than one million vehicles and a large number of small industries. High levels of air pollutants are thus detected. The purpose of this work consists in applying air quality modelling tools to the region of Bogota, aiming to acquire a deeper understanding of the factors that originate air pollution in the city, and of the way pollutants are dispersed and chemically transported. Furthermore, the knowledge gained is used to propose and evaluate air pollution abatement strategies. In the first part of this thesis, two versions of the traffic emission inventory are generated, one using standard CORINAIR traffic emission factors and the other using bulk real-world traffic emission factors. Both emission inventories are compared and evaluated with the help of numerical simulations. The emission inventory calculated using bulk real-world traffic emission factors generates simulated concentrations closer to the observed values. Thus, an innovative technique consisting in the combination of measurements and modelling to estimate and evaluate traffic emissions is proposed in this part of the study. In the second part, mesoscale meteorological and air quality models are applied to the city. The wind pattern developed over the complex topography of the region and the development of the plume of pollutants are simulated with success. In the third part of this work, the air quality model is used to study the plume of pollution in terms of the governing chemical regimes and the individual and combined effects of the main sources of emission. Traffic is the major contributor to the plume of pollutants in Bogota. Three feasible emission scenarios which are addressed to the mitigation of emissions from heavy traffic are evaluated with the model. Whereas reductions are attained for primary pollutants and aerosols (whose simulation is presented in the forth part of this work), levels of Ozone increase with these scenarios. The air quality model indicates that strategies directed to mitigate air pollution might have contradictory effects depending on the pollutant to be tackled. Air quality modelling proved to be a very useful tool for evaluating emission scenarios in advance and prioritizing actions to mitigate pollution in Bogota.

EPFL2007