Ian Longley

The influence of vegetation on the horizontal and vertical distribution of pollutants in a street canyon.

Space constraints in cities mean that there are only limited opportunities for increasing tree density within existing urban fabric and it is unclear whether the net effect of increased vegetation in street canyons is beneficial or detrimental to urban air quality at local scales. This paper presents data from a field study undertaken in Auckland, New Zealand designed to determine the local impact of a deciduous tree canopy on the distribution of the oxides of nitrogen within a street canyon. The results showed that the presence of leaves on the trees had a marked impact on the transport of pollutants and led to a net accumulation of pollutants in the canyon below the tree tops. The incidence and magnitude of temporally localised spikes in pollutant concentration were reduced within the tree canopy itself. A significant difference in pollutant concentrations with height was not observed when leaves were absent. Analysis of the trends in concentration associated with different wind directions showed a smaller difference between windward and leeward sides when leaves were on the trees. A small relative increase in concentrations on the leeward side was observed during leaf-on relative to leaf-off conditions as predicted by previous modelling studies. However the expected reduction in concentrations on the windward side was not observed. The results suggest that the presence of leaves on the trees reduces the upwards transport of fresh vehicle emissions, increases the storage of pollutants within the canopy space and reduces the penetration of clean air downwards from aloft. Differences observed between NO and NO(2) concentrations could not be accounted for by dispersion processes alone, suggesting that there may also be some changes in the chemistry of the atmosphere associated with the presence of leaves on the trees.

Variations in exposure to traffic pollution while travelling by different modes in a low density, less congested city

This research assessed the comparative risk associated with exposure to traffic pollution when travelling via different transport modes in Christchurch, New Zealand. Concentrations of PM1, UFPs and CO were monitored on pre-defined routes during the morning and evening commute on people travelling concurrently by car, bus and bicycle. It was found that car drivers were consistently exposed to the highest levels of CO; on-road cyclists were exposed to higher levels of all pollutants than off-road cyclists; car and bus occupants were exposed to higher average levels of UFP than cyclists, and travellers were occasionally exposed to very high levels of pollution for short periods of time. PM10 and PM2.5 were found to be poor indicators of exposure to traffic pollution. Studying Christchurch adds to our understanding as it was a lower density city with limited traffic congestion compared most other cities previously studied.

Uptake of methanol to the North Atlantic Ocean surface

An anticorrelation between atmospheric methanol (CH 3 OH) concentrations and wind speed and a positive correlation between dimethylsulphide (DMS) concentrations and wind speed have been observed at the coastal air monitoring site of Mace Head in Ireland, during a period of cyclonic activity in which the averaged surface wind speed changed substantially as a low-pressure system evolved over the northeast Atlantic. These observations suggest a net air-to-sea flux of CH 3 OH. This conclusion is supported by the good agreement between the wind speed dependencies of the measured gas concentrations and theoretical predictions using wind-induced turbulent gas transfer velocities of DMS and CH 3 OH calculated from a resistance model, embedded in a photochemical box model. For a wind speed of 8 m s -1 , an ocean deposition rate of methanol of between 0.02 and 0.33 cm s -1 is calculated, with a best estimate of 0.09 cm s -1 , in good agreement with deposition rates used in global models and derived from atmospheric budgets. The large uncertainty in the calculated deposition rates is due almost entirely to the uncertainty in the degree of saturation of methanol in the surface ocean, highlighting the critical requirement for measurements of methanol in seawater. Owing to the dependence on wind speed, the deposition rates calculated showed substantial range and the calculated contribution of ocean deposition to total loss of CH 3 OH (ocean uptake and gas phase OH oxidation) varied from approximately 20% to 60%.

Spatio-temporal PM 2.5 prediction by spatial data aided incremental support vector regression

Machine learning requires sufficient and reliable data to enhance the prediction performance. However, environmental data sometimes is short and/or contains missing data. Often existing prediction models built on machine learning fail to predict environmental problems accurately. We argue that spatial domain data can be used to facilitate the training of temporal prediction model. This paper formulates mathematically a spatial data aided incremental support vector regression (SalncSVR) for spatio-temporal PM2.5 prediction. We conduct spatio-temporal PM2.5 prediction over 13 monitoring stations in Auckland New Zealand, and compare the proposed SalncSVR with a pure temporal IncSVR prediction.

Proximity to busy highways and local resident perceptions of air quality

This study investigated variations in perceptions of air quality as a function of residential proximity to busy highways, across two suburbs of South Auckland, New Zealand. While plenty is known about the spatial gradients of highway emissions, very little is known about variation of lay understanding at the fine spatial scale and whether there are gradients in severity of concerns. One-hundred and four near-highway residents agreed to participate in a semi-structured interview on their knowledge and attitudes towards highway traffic emissions. Proximity to the highway edge varied within 5-380 m at the predominantly downwind side of the highway and 13-483 m at the upwind side. Likert-type ordered response questions were analysed using multivariate regression. Inverse linear relationships were identified for distance from highway and measures of concern for health impacts, as well as for noise (p<0.05). Positive linear relationships were identified for distance from highway and ratings of both outdoor and indoor air quality (p<0.05). Measures of level of income had no conclusive statistically significant effect on perceptions. Additional discussion was made surrounding participants open-ended responses, within the context of limited international research. Findings indicate that there may be quantifiable psychological benefits of separating residents just a short distance (40 m+) from highways and that living within such close proximity can be detrimental to wellbeing by restricting local outdoor activity. This work lends additional rationale for a residential separation buffer of ~100 m alongside major highways in the interests of protecting human health.

CityFlux perfluorocarbon tracer experiments

CityFlux perfluorocarbon tracer experiments F. K. Petersson, D. Martin, I. R. White, S. J. Henshaw, G. Nickless, I. Longley, C. J. Percival, M. Gallagher, and D. E. Shallcross School of Chemistry, University of Bristol, Bristol, UK SEAS, University of Manchester, Manchester, UK now at: Ionicon Analytik Gesellschaft m.b.H., Innsbruck, Austria now at: National Institute of Water and Atmospheric Research, New Zealand Received: 30 September 2009 – Accepted: 3 December 2009 – Published: 5 January 2010 Correspondence to: D. E. Shallcross (d.e.shallcross@bristol.ac.uk) Published by Copernicus Publications on behalf of the European Geosciences Union.

EXPOSURE TO ULTRAFINE PARTICLES FROM TRAFFIC IN CITY STREETS AND THE URBAN ATMOSPHERE

Mass-based emission controls are successfully reducing pollutant levels of fine particles from road vehicles, but may have actually increased the emission of ultrafine particles and their persistence in the atmosphere just as growing evidence indicates that these ultrafine particles present the greatest threat to health upon inhalation. These particles have so little mass that they barely register in measurements made by current urban air quality monitoring networks, which measure mass of particulate matter (PM-sub-10). Current daily/hourly monitoring of PM-sub-10 for the purposes of air quality management fails to represent the wide variation and episodicity in exposure of an urban population to the threat from traffic-sourced ultrafine particles. In order to quantify and interpret this variability, data from experiments employing sophisticated, high-resolution instrumentation in U.K. cities is offered. This data illustrates the variability on time scales from minutes to hours of ultrafine particle exposure on busy streets, and shows how meteorological factors and urban topography determine the exposure to traffic particle emissions in the surrounding urban environment. Such information has key consequences for the assessment of future emission reduction and air quality improvement strategies, especially localized ones.

Vegetation diversity protects against childhood asthma: results from a large New Zealand birth cohort

We assessed the association between the natural environment and asthma in 49,956 New Zealand children born in 1998 and followed up until 2016 using routinely collected data. Children who lived in greener areas, as measured by the normalized difference vegetation index, were less likely to be asthmatic: a 1 s.d. increase in normalized difference vegetation index was associated with a 6.0% (95% CI 1.9–9.9%) lower risk of asthma. Vegetation diversity was also protective: a 1 s.d. increase in the number of natural land-cover types in a child’s residential meshblock was associated with a 6.7% (95% CI 1.5–11.5%) lower risk. However, not all land-cover types were protective. A 1 s.d. increase in the area covered by gorse (Ulex europaeus) or exotic conifers, both non-native, low-biodiversity land-cover types, was associated with a 3.2% (95% CI 0.0–6.0%) and 4.2% (95% CI 0.9–7.5%) increased risk of asthma, respectively. The results suggest that exposure to greenness and vegetation diversity may be protective of asthma.Study over 18 years of nearly 50,000 children in New Zealand, measuring the impact of vegetation diversity on the incidence and prevalence of childhood asthma. An increase in the diversity of vegetation in a child’s residential neighbourhood is associated with a lower risk of developing asthma.

A Simple Tool to Identify Representative Wind Sites for Air Pollution Modelling Applications

This paper investigates the use of the Site-Optimized Semiempirical (SOSE) air pollution model to identify the surface wind measurement site characteristics that yield the best air pollution predictions for urban locations. It compares the modelling results from twelve meteorological sites with varying anemometer heights, located at different distances from the air pollution measurements and exhibiting different land use characteristics. The results show that the index of agreement (IA) between observed and predicted concentrations can be improved from 0.4 to 0.8 by using the most compared to the least representative wind data as input to the air pollution model. Although improvements can be achieved using wind data from a site closer to the air quality monitoring site, choosing the closest wind site does not necessarily yield the best results, especially if the meteorological station is located in a region of complex land use. In addition, both the height of the anemometer and the openness of the terrain surrounding the anemometer were found to be equally important in obtaining good model predictions. The simple SOSE model can therefore be used to complement regulatory meteorological guidelines by providing a quantitative assessment of wind site representativeness for air quality applications in complex urban environments.

What is sustainable air quality

For 40 years or more, air quality policy has been based on the paradigm of the air quality standard as a uniform criterion of acceptable environmental degradation, built on the foundations of the precautionary principle. However, developments in health science have undermined some of the underlying assumptions of this paradigm whilst technological emission controls have been offset by growing economic activity. Current trends are towards increasingly demanding notions of what constitutes acceptable air quality. Proposed future air quality standards could require a revolution in urban form and infrastructure. We need a new paradigm - sustainable air quality. In this paper, we discuss the need for a new paradigm of sustainable air quality management, its basis and what it might hope to achieve, including how further downward pressure can be exerted on emissions through urban form, urban design, transport policy and projects, energy strategy, etc.