Knut Erik Grønskei

Air pollution exposure monitoring and estimation. Part II. Model evaluation and population exposure

The air pollution dispersion model EPISODE has been developed at the Norwegian Institute for Air Research (NILU) over the past several years in order to meet the needs of modern air quality management work in urban areas. The model has recently been used as a basis for exposure calculations of NOx and NO2 in order to assess the effects of different traffic diversion measures on health and well being for the residents in the Vålerenga-Ekeberg-Gamlebyen area in Oslo. Here we describe some results from the most recent evaluations of the model for NOx and NO2 at station Nordahl Brunsgate in Oslo for the period 1 October 1996-19 November 1996. In addition examples of population exposure calculations for Oslo performed during the winter period of 1995-96, are also presented.

Air pollution exposure monitoring and estimating. Part I. Integrated air quality monitoring system

This paper presents an integrated exposure monitoring system, based on an expansion of existing air quality monitoring systems using dispersion modelling. The system allows: (1) identifying geographical areas whose inhabitants are most exposed to ambient pollution; (2) identifying how many people in an area are exposed to concentrations of pollution exceeding air quality guidelines; (3) describing the exposure of population subgroups (e.g. children); (4) planning pollution abatement measures and quantifying their effects; (5) establishing risk assessment and management programs, and (6) investigating the short- and long-term effects of both pollutants and pollution sources on public health. The effect of pollution is rarely very large and in order to discover it, exposure estimation must provide data that reflects both spatial and temporal variations. Estimates of pollution exposure are obtained using an integrated approach that combines results of measurements from monitoring programs with dispersion calculations. These values can serve as estimates for individual short-term or long-term exposure. The grouped data allows the expression of ambient pollution concentrations as the spatial distribution of estimates such as the mean or 98th percentile of such compounds as SO2, O3, NO2, PM10 and PM2.5. This integrated approach has been combined into a single software package, AirQUIS.

Air pollution exposure monitoring and estimation. Part V. Traffic exposure in adults

In Oslo, traffic has been one of the dominating sources of air pollution in the last decade. In one part of the city where most traffic collects, two tunnels were built. A series of before and after studies was carried out in connection with the tunnels in use. Dispersion models were used as a basis for estimating exposure to nitrogen dioxide and particulate matter in two fractions. Exposure estimates were based on the results of the dispersion model providing estimates of outdoor pollutant concentrations on an hourly basis. The estimates represent concentrations in receptor points and in a square kilometre grid. The estimates were used to assess development of air pollution load in the area, compliance with air quality guidelines, and to provide a basis for quantifying exposure-effect relationships in epidemiological studies. After both tunnels were taken in use, the pollution levels in the study area were lower than when the traffic was on the surface (a drop from 50 to 40 micrograms m-3). Compliance with air quality guidelines and other prescribed values has improved, even if high exposures still exist. The most important residential areas are now much less exposed, while areas around tunnel openings can be in periods exposed to high pollutant concentrations. The daily pattern of exposure shows smaller differences between peak and minimum concentrations than prior to the traffic changes. Exposures at home (in the investigation area) were reduced most, while exposures in other locations than at home showed only a small decrease. Highest hourly exposures are encountered in traffic.

Air pollution exposure monitoring and estimation. Part IV. Urban exposure in children

In the winter of 1994, 2300 school-age children in Oslo participated in a panel study of the role of traffic pollution on the exacerbation of diseases of the respiratory system and other symptoms of reduced health and well being in children. The children filled out a diary daily with information for five time points over six weeks. In order to quantify exposure-effect relationships for the symptoms, individual exposure to NO2 and particulate matter (PM2.5) was estimated, using the DINEX method a combination of information from the diary as to the childrens whereabouts during the five time points each day, coupled with continuous dispersion modelling. An individual exposure estimate for each time point for each child was defined. Individual exposure estimated using dispersion modelling can be used to examine patterns of exposure such as isolating geographic areas with higher concentrations or describing concentrations of pollution by time of day. The diary allowed the time-use of the children to be described.

Evaluation of a model for hourly spatial concentration distributions

Abstract A time-dependent finite difference model in three levels combined with a puff model to account for subgrid effects close to single sources was used to calculate hour-to-hour concentration distributions. Measurements from several selected stations were used to account from time variation in background concentrations. For each hour, weight was given to observed values in areas that were not influenced by local sources. Results of concentration calculations based on hourly data on emission and dispersion are validated by measured time series of SO2 and NOx at five stations. A combination of hourly nephelometer readings and 12-h measurements of small particles at three stations are compared with calculated values. Hourly observed and calculated values from two periods (3 January–15 March 1988 and 18 April–24 June 1988) were used for the evaluation of the model for calculating hourly pollution concentrations in each square kilometre. The results showed that prediction of short-term average concentrations (e.g. hourly data) are usually poorly correlated with observations at the same time and location. Slight displacement errors may cause point-to-point correlation to be poor as a result of errors in input data. The pattern of NOx concentration variation with time was reproduced well at all stations. A subgrid model taking into account the influence of nearby roads would probably improved the model for NOx at some stations. For SO2 and small particles, industrial sources have the dominant influence and the correspondence between observed and calculated values were improved by taking into account spatial uncertainty and an hourly variation in background concentrations.

Air pollution exposure monitoring and estimation . Part VI. Ambient exposure of adults in an industrialised region

This paper presents methodology and results of a dynamic individual air pollution exposure model (DINEX) that calculates the hourly exposure for each adult in a panel study. Each of over 260 participants, through the use of a diary, provided information used in the model to calculate his/her personal, individualised exposure. The participants filled out the diary daily, hour by hour, over two, two month periods. The exposure assessment model coupled the diary information and results of an indoor/outdoor measurement program, with the results of dispersion modelling on an hourly basis for an industrial area in Norway. The estimated air pollution concentrations from the dispersion model, based on continuous meteorological measurements, were calibrated with air pollutant concentrations measured continuously.

Verification of Urban Scale Time-Dependent Dispersion Model with Subgrid Elements, in Oslo, Norway

Results from monitoring of air pollution concentrations in cities in Norway have shown that nitrogen dioxide (NO2) is one of the compounds which most often, and to the largest extent, exceeds current air quality guidelines (Hagen, 1992; Larssen, 1993). This is the case both in city streets and in the urban atmosphere in general. In Norway, the highest NO2 concentrations occur during the winter months, in connection with “episodes” with poor dispersion. In the general urban atmosphere, high 24-hour average values are of greatest concern relative to Air Quality Guideline (AQG), while in the street atmosphere, very high peak (hourly) concentrations may be the most important problem.

Air pollution exposure monitoring and estimation VII. Estimation of population exposure in a central European airshed

In order to clarify the local variation in exposure and source-receptor relationships, a dispersion model for estimating air pollution concentrations was developed for a polluted area in the Czech Republic. Three models characterized by different spatial resolution were integrated into one modelling tool. A regional-scale dispersion model accounted for pollution contribution from sources outside the modelling area. Local- and urban-scale dispersion models were used to calculate local concentration distributions. Calculated concentration distributions were evaluated. Deviations between observed and calculated concentrations were not correlated in space, except in episodes, and concentrations measured at spatially representative stations were assimilated into the model results using statistical interpolation (simple kriging). The results indicated that centralized heating plants and local home heating were the most important sources for sulfur dioxide (SO2) pollution. Both high and low level sources may contribute to the accumulation of pollution concentrations in episodes. The measured concentrations were important for the description of distributions in episodes characterized by complex wind and dispersion conditions. The applicability of source oriented model calculations to correctly represent measured concentrations in the pollution episodes was limited due to the fact that meteorological conditions representative of high concentration episodes were characterized by very low wind speed and variable wind directions. About 8,000 individuals were given an exposure estimate representing contribution from local emissions, based on the estimated hourly outdoor exposure to SO2 at their home/work addresses in the 3 month study period in the autumn of 1991. The results showed that, for 5% of participants, the maximum hourly contribution of local emissions was over 380 microg m(-3). For the 3 month average, both large-scale and local-scale pollution contribute significantly. For primary compounds, such as SO2, steep gradients are observed in the vicinity of strong local sources. These gradients are important for exposure characteristics and health effect quantification, and often will not be captured by an existing monitoring network. The calculations can be extended to other periods or to different compounds.

Oxidant Formation Described in a Three Level Grid

In Grenland, Norway, a combination of industrial emissions and urban areas may cause high oxidant episodes. To clarify the local oxidant formation potential within the area, a model describing both photochemical and dispersion effects was developed. This paper describes the results of a cooperation between Institute of Geophysics, University of Oslo, and Norwegian Institute for Air Research (NILU) (1).

Description of Vertical Dispersion under Influence of Roughness Elements

Increased mixing downwind of roughness elements influences the dilution of local emission as well as the dry deposition of pollution from distant sources.