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The paper analyzes experimental markets where subjects buy and sell two different assets. The assets' properties vary across treatments, and their relative price is the exchange rate. Although both assets uniformly exhibit bubbles, the exchange rate satisfies cross‐currency arbitrage. There is no evidence of a positive risk premium in these markets, and almost all subjects' forecasts of the exchange rate are rational.

Evidence to advocate for cleaner air for people with asthma is not in short supply. We know that air pollution is associated with the development and worsening of the condition and that mitigating interventions can improve respiratory outcomes. We have clear targets, particularly traffic emissions, especially in urban areas, and plenty of potentially effective actions. Road traffic must be reduced, and what remains should be cleaner and greener. Urban green spaces, safe cycle networks and wider pavements will promote active travel and leisure time exercise. Healthcare professionals must ensure people are aware of their air quality, its impact on asthma and the appropriate behaviour to safeguard health. What remains are realistic policies and effective measures, based on the correct scientific evidence, to be taken forth with political courage and investment so that air pollution no longer contributes to the development or worsening of respiratory ill health.

Sean David Beevers, David Carlin Carslaw, David Dajnak, Gregor B Stewart, Martin Lloyd Williams, Julia C Fussell, Frank James Kelly MRC-PHE Centre for Environment and Health, Facility of Life Sciences and Medicine, King's College, London, UK Abstract: Air pollution strategies in London over the last 12 years have centered upon the congestion charging scheme, and at the same time, the fitting of particle traps to London buses, the low emissions zone (LEZ), and the Mayor's Air Quality Strategy (MAQS). The 2003 congestion charging scheme achieved much of the scheme's aims, but the demand to travel and the need for road space eroded the initial benefits. While fitting particle traps on buses was predicted to reduce particulate matter (PM) exhaust emissions, the introduction of phases 1 and 2 of the LEZ and MAQS strategies were both predicted to have modest emission impacts. Reliance on new Euro-standard vehicles to reduce emissions, and as a way of designing LEZs, has been problematic, with oxides of nitrogen (NOx) and nitrogen dioxide (NO2) emissions from diesel vehicles reducing less than predicted. Consequently, the UK has not met annual NO2 European Union (EU) limit values, necessitating a time extension application. A mismatch between PM10 ambient trends and emissions has also been reported, with the long-term performance of PM particle filters remaining an important question. Assessing London's traffic management schemes has relied upon emission inventories and dispersion models, and to date, there has been no confirmation of the effects of the schemes using ambient data, a challenging and important area of research. However, measurements of ambient NOx, NO2, ozone, PM species, and roadside vehicle emissions have all contributed to the improvement of road traffic emission inventories in London, and it remains important to undertake ambient monitoring to assess future schemes. Looking forward, the real-world emissions performance of Euro 6/VI vehicles, selective catalytic reduction, and the ultra-low emissions zone in London will play a critical role in meeting EU limit values for ambient NO2, and in light of the increasing health evidence of urban air pollution, policy makers should aim to reduce PM concentrations toward health-based World Health Organization guideline values. Keywords: congestion charging, low emissions zone, traffic management, NOx, PM10 vehicle emissions

Abstract
The Environment Act (2021) requires the government to set at least one long-term air-quality target, as well as a target for fine particulate matter (PM2.5) air pollution. COMEAP provided independent expert advice to the Department for Environment, Food and Rural Affairs (Defra) to inform the development of targets to reduce both the annual average (mean) concentration of PM2.5 in ambient air and long term population exposures. COMEAP's advice includes that: a focus on reducing long-term average concentrations of PM2.5 is appropriate evidence indicates that PM2.5 pollution can have harmful effects on people's health at low concentrations reducing concentrations to, or below, the World Health Organization's new Air Quality Guideline (5 µg/m3) would benefit public health available studies have not indicated a threshold of effect below which there is no harm reducing exposure of the whole population would achieve the greatest overall public health benefit some individuals or groups are more at risk, but it might be difficult to reflect this in a national targets framework the health benefits of reducing other pollutants, such as nitrogen dioxide and ozone, should not be overlooked. In response to Defra's evidence report explaining the rationale for its proposed targets, COMEAP: recommended that Defra should consider roles in continuing to improve air quality, even where legally binding targets are met suggested that interim targets would be important to ensure early progress and maximise health benefits stressed the importance of considering inequalities noted that international engagement will be required

Abstract
Statement from the Committee on the Medical Effects of Air Pollutants (COMEAP) on the differential toxicity of particulate matter according to source or constituents
Particulate matter in outdoor air comes from a wide range of different sources and contains many different chemical components. Understanding which of these sources and components are particularly harmful would help to focus policies and interventions to reduce impacts on health. COMEAP recently (July 2022) published an updated statement on this topic, drawing on recent reviews of the available evidence. It noted that particulate matter, and constituents of particulate matter, associated with combustion and road traffic have received the most research attention. However, there was insufficient coherence in the epidemiological evidence to conclude that these sources of particulate matter play a significantly greater role in the health effects of particulate air pollution than other sources or constituents. A comprehensive review of the evidence reveals that toxicity has been attributed to a wide variety of constituents and sources, possibly acting by a number of different mechanisms. However, the complexity of sources, sizes and chemical composition of particulate matter makes it extremely difficult to identify which characteristics of particles might make them less harmful or more toxic than others. Future research assessing the influence of chemical composition of particulate matter should offer greater insights into toxicity. But, at present, PM2.5 (the mass concentration of fine particulate matter in air) remains the most suitable metric for evaluating health impacts and regulating particulate air pollution.

Air pollution strategies in London over the last 12 years have centered upon the congestion charging scheme, and at the same time, the fitting of particle traps to London buses, the low emissions zone (LEZ), and the Mayor's Air Quality Strategy (MAQS). The 2003 congestion charging scheme achieved much of the scheme's aims, but the demand to travel and the need for road space eroded the initial benefits. While fitting particle traps on buses was predicted to reduce particulate matter (PM) exhaust emissions, the introduction of phases 1 and 2 of the LEZ and MAQS strategies were both predicted to have modest emission impacts. Reliance on new Euro-standard vehicles to reduce emissions, and as a way of designing LEZs, has been problematic, with oxides of nitrogen (NOx) and nitrogen dioxide (NO2) emissions from diesel vehicles reducing less than predicted. Consequently, the UK has not met annual NO2 European Union (EU) limit values, necessitating a time extension application. A mismatch between PM10 ambient trends and emissions has also been reported, with the long-term performance of PM particle filters remaining an important question. Assessing London's traffic management schemes has relied upon emission inventories and dispersion models, and to date, there has been no confirmation of the effects of the schemes using ambient data, a challenging and important area of research. However, measurements of ambient NOx, NO2, ozone, PM species, and roadside vehicle emissions have all contributed to the improvement of road traffic emission inventories in London, and it remains important to undertake ambient monitoring to assess future schemes. Looking forward, the real-world emissions performance of Euro 6/VI vehicles, selective catalytic reduction, and the ultra-low emissions zone in London will play a critical role in meeting EU limit values for ambient NO2, and in light of the increasing health evidence of urban air pollution, policy makers should aim to reduce PM concentrations toward health-based World Health Organization guideline values.