David Carslaw

The University of York · Department of Chemistry

Direct measurements of NOx concentration and flux were made from a tall tower in central London, UK as part of the Clean Air for London (ClearfLo) project. Fast time resolution (10 Hz) NO and NO2 concentrations were measured and combined with fast vertical wind measurements to provide top-down flux estimates using the eddy covariance technique. Mea...

In this paper we report the first direct measurements of nitrogen dioxide (NO2) in the UK using a vehicle emission remote sensing technique. Measurements of NO, NO2 and ammonia (NH3) from almost 70,000 vehicles were made spanning vehicle model years from 1985 to 2012. These measurements were carefully matched with detailed vehicle information data...

openair is an R package primarily developed for the analysis of air pollution measurement data but which is also of more general use in the atmospheric sciences. The package consists of many tools for importing and manipulating data, and undertaking a wide range of analyses to enhance understanding of air pollution data. In this paper we consider t...

Ambient trends in nitrogen oxides (NOx) and nitrogen dioxide (NO2) for many air pollution monitoring sites in European cities have stabilised in recent years. The lack of a decrease in the concentration of NOx and in particular NO2 is of concern given European air quality standards are set in law. The lack of decrease in the concentration of NOx an...

A statistical analysis of roadside concentrations of nitrogen oxides (NOX) and nitrogen dioxide (NO2) in London shows that from 1997 to 2003 there has been a statistically significant downward trend (at the p=0.004 level) in NOX averaged across a network of 36 sites. Conversely, there has been no statistically significant trend in the concentration...

We develop a new technique called plume regression where fast response instruments located at the roadside are used to measure exhaust plumes of passing vehicles. The approach is used to generate highly disaggregated vehicle emissions information by vehicle type, which compares well with traditional vehicle emission remote sensing. Additionally, th...

Indoor sources of air pollution, such as from cooking and cleaning, play a key role in indoor gas-phase chemistry. The focus of the impact of these activities on air quality...

This study uses mobile monitoring to gain a better understanding of particulate matter (PM) sources in two areas of Central and Outer London, UK. We find that, unlike emissions of nitrogen oxides (NO + NO2 = NOx), which are elevated in Central London due to the high number of diesel vehicles and congestion, fine particulate matter (PM2.5) emissions...

The promotion and growth in the use of diesel fuel in passenger cars in the UK and Europe over the past two decades led to considerable adverse air quality impacts in urban areas and more widely. In this work, we construct a multi-decade analysis of passenger car emissions in the UK based on real driving emissions data. An important part of the stu...

The development of remote emission sensing techniques such as plume chasing and point sampling has progressed significantly and is providing new insight into vehicle emissions behaviour. However, the analysis of remote emission sensing data can be highly challenging and there is currently no standardised method available. In this study we present a...

Modern gasoline and diesel vehicles are equipped with highly effective emission control systems that result in low emissions of pollutants such as nitrogen oxides (NOx) when new. However, with increasing age or mileage, the emissions performance of vehicles can deteriorate over time, leading to increased emissions. In this work we use comprehensive...

The global COVID-19 pandemic that began in late December 2019 led to unprecedented lockdowns worldwide, providing a unique opportunity to investigate in detail the impacts of restricted anthropogenic emissions on air quality. A wide range of strategies and approaches exist to achieve this. In this paper, we use the “deweather” R package, based on B...

Portable Emission Measurement Systems (PEMS) are commonly used to measure absolute (mass per unit distance) emissions of a range of pollutants from road vehicles under real driving conditions. Because measuring large numbers of vehicles with PEMS is impractical, this paper investigates how vehicle emission remote sensing device (RSD) can supplement...

Over the last 2 decades, the importance of emissions source types of atmospheric pollutants in urban areas has undergone significant change. In particular, there has been a considerable reduction in emissions associated with road vehicles. Understanding the role played by different source sectors is important if effective air pollution control is t...

Recent evidence suggests NH3 emissions from road vehicles play an important role in the formation of fine particulate matter, especially in urban areas. However, there is little data available for NH3 emitted from road vehicles under real driving conditions, in part due to its lack of regulation in vehicle emission legislation. In this study, we us...

The importance of emissions source types in urban areas has undergone significant changes over the past two decades. In particular, there has been a considerable reduction in emissions associated with road vehicles. Understanding the role played by different source sectors is important if effective air pollution control is to be achieved. Current a...

Road vehicles make important contributions to a wide range of pollutant emissions from the street level to global scales. The quantification of emissions from road vehicles is, however, highly challenging given the number of individual sources involved and the myriad factors that influence emissions such as fuel type, emission standard, and driving...

In March 2020, non-pharmaceutical intervention measures in the form of lockdowns were applied across Europe to urgently reduce the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus which causes the COVID-19 disease. The aggressive curtailing of the European economy had widespread impacts on the atmospheric comp...

In this study we use comprehensive vehicle emission remote sensing measurements of over 230,000 passenger cars to estimate total UK ammonia (NH 3) emissions. Estimates are made using 'top-down' and 'bottom-up' methods that demonstrates good agreement to within 1.1% for total fuel consumed or CO 2 emitted. A central component of this study is the co...

In March 2020, non-pharmaceutical interventions in the form of lockdowns were applied across Europe to urgently reduce the transmission of SARS-CoV-2, the virus which causes the COVID-19 disease. The near-complete shutdown of the European economy had widespread impacts on atmospheric composition, particularly for nitrogen dioxide (NO2) and ozone (O...

Volatile organic compounds (VOCs) are a broad class of air pollutants which act as precursors to tropospheric ozone and secondary organic aerosols. Total UK emissions of anthropogenic VOCs peaked in 1990 at 2,840 kt yr ⁻¹ and then declined to approximately 810 kt yr ⁻¹ in 2017 with large reductions in road transport and fugitive fuel emissions. The...

Vehicle emission remote sensing has the potential to provide detailed emissions information at a highly disaggregated level owing to the ability to measure thousands of vehicles in a single day. Fundamentally, vehicle emission remote sensing provides a direct measure of the molar volume ratio of a pollutant to carbon dioxide, from which fuel-based...

The Dieselgate scandal which broke in September 2015 demonstrated that vehicle manufacturers, such as the Volkswagen Group (VWG) engaged in software-based manipulation which led to vehicles passing laboratory-based emission testing limits, but were far more polluting while being driven on roads. Using 23000 on-road remote sensing measurements of li...

Abstract number 488377 and final paper number A21W-2634

This study analyses comprehensive European remote sensing data to better understand deterioration effects on passenger cars’ emissions of NOx (including NO2), CO and hydrocarbons (HC).

The Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) programme is an international collaborative project focusing on understanding the sources, processes and health effects of air pollution in the Beijing megacity. APHH-Beijing brings together leading China and UK research groups, state-of-the-art infrastructure and air q...

Diesel-powered road vehicles are important sources for nitrogen oxide (NOx) emissions and the European passenger fleet is highly dieselised, which has resulted in many European roadside environments being non-compliant with legal air quality standards for nitrogen dioxide (NO2). Based on vehicle emission remote sensing data for 300 000 light-duty v...

Trend analysis of air pollutant concentrations becomes problematic when applied to data from air quality monitoring networks containing time series of differing lengths. The average trend from such data can be misleading due to biases in the monitoring network. For example, if new monitoring sites located in more polluted locations are added to a n...

The direct emission of nitrogen dioxide (NO2) from road vehicle exhaust has been an important contributor to near-road ambient concentrations of NO2 in many European cities. Diesel vehicles and their use of emission control technologies such as Diesel Oxidation Catalysts, have dominated the emission of NO2 from road vehicles. In this work, we summa...

APHH-Beijing (Atmospheric Pollution and Human Health in a Chinese Megacity) is an international collaborative project to examine the emissions, processes and health effects of air pollution in Beijing. The four research themes of APHH-China are: (1) sources and emissions of urban atmospheric pollution; (2) processes affecting urban atmospheric poll...

Interventions used to improve air quality are often difficult to detect in air quality time series due to the complex nature of the atmosphere. Meteorological normalisation is a technique which controls for meteorology/weather over time in an air quality time series so intervention exploration (and trend analysis) can be assessed in a robust way. A...

Meteorological normalisation is a technique which accounts for changes in meteorology over time in an air quality time series. Controlling for such changes helps support robust trend analysis because there is more certainty that the observed trends are due to changes in emissions or chemistry, not changes in meteorology. Predictive random forest mo...

Remote sensing can measure the emission rates from a large number of road vehicles in passing. This report presents a method to compare results with emission rates from legislative testing programs.

Remote sensing is a technique to monitor real driving emissions from on-road fleets, vehicle groups and possibly individual vehicles. Here, applications of remote vehicle emission sensing are discussed with the view of a more widespread application in Europe. Measuring real driving emissions is highly relevant for ensuring that air quality standar...

In this report a new, collaborative dataset from Remote Sensing campaigns conducted in Europe between 2011 and 2017 is analysed. The focus is on NOx emissions from light-duty diesel vehicles: Average emission rates, emission rates by manufacturer and by engine family are presented. Their dependence on mileage/age as well as ambient temperature is d...

Many European countries do not meet legal air quality standards for ambient nitrogen dioxide (NO2) near roads; a problem that has been forecasted to persist to 2030. Although European air quality standards regulate NO2 concentrations, emissions standards for new vehicles instead set limits for NOx—the combination of nitric oxide (NO) and NO2. From...

The present study involves the first attempt to pool the remote sensing data that has been collected across Europe since 2011 into one common database, with the primary aim to analyse the real-driving emission performance of Euro 5 and 6 light-duty diesel vehicles across the European fleet. These measurements total around 500,000 remote sensor read...

Implications: Synchronized remote sensing measurements of NO were taken using two different remote sensing devices in an off-road study. It was found that the measurements taken by both instruments were well correlated. Fractional NO2 measurements from a prior study, measurable on only one device, were used to create new NOx emission factors for t...

Long-term atmospheric NOx/CO enhancement ratios in megacities provide evaluations of emission inventories. A fuel-based emission inventory approach that diverges from conventional bottom-up inventory methods explains 1970–2015 trends in NOx/CO enhancement ratios in Los Angeles. Combining this comparison with similar measurements in other U.S. citie...

This paper outlines the development of enhanced bivariate polar plots that allow the concentrations of two pollutants to be compared using pair-wise statistics for exploring the sources of atmospheric pollutants. The new method combines bivariate polar plots, which provide source characteristic information, with pair-wise statistics that provide in...

Long-term atmospheric NOx/CO enhancement ratios in megacities provide evaluations of emission inventories. A fuel-based emission inventory approach that diverges from conventional bottom-up inventory methods explains 1970?2015 trends in NOx/CO enhancement ratios in Los Angeles. Combining this comparison with similar measurements in other U.S. citie...

Urban case studies: general discussion

Reducing ambient concentrations of nitrogen dioxide (NO2) remains a key challenge across many European urban areas; particularly close to roads. This challenge mostly relates to the lack of reduction in emissions of oxides of nitrogen (NOx) from diesel road vehicles relative to the reductions expected through increasingly stringent vehicle emission...

To date, direct validation of city-wide emissions inventories for air pollutants has been difficult or impossible. However, recent technological innovations now allow direct measurement of pollutant fluxes from cities, for comparison with emissions inventories, which are themselves commonly used for prediction of current and future air quality and...

In the developed world we spend most of our time indoors, where we receive the majority of our exposure to air pollution. This paper reports model simulations of PM2.5 and ozone concentrations in identical landscape offices in three European cities: Athens, Helsinki and Milan. We compare concentrations during an intense heatwave in August 2003 with...

Abstract An evaluation has been made of a number of contrasting atmospheric chemical transport models, of varying complexity, applied to estimate sulphur and nitrogen deposition in the UK. The models were evaluated by comparison with annually averaged measurements of gas, aerosol and precipitation concentrations from the national monitoring network...

This work presents the first comprehensive real-world emissions results from urban buses retrofitted with an optimised low-NO2 selective catalytic reduction (SCR) system. The SCRT system combines a CRT (Continuously Regenerating Trap) to reduce particle emissions and SCR to reduce NOx emissions. The optimised low-NO2 SCRT was designed to work under...

In this paper a new receptor modelling method is developed to identify and characterise emission sources. The method is an extension of the commonly used conditional probability function (CPF). The CPF approach is extended to the bivariate case to produce a conditional bivariate probability function (CBPF) plot using wind speed as a third variable...

A new model (INDAIR-CHEM) has been developed by combining a detailed indoor air chemistry model with a physical and probabilistic multi-compartment indoor/outdoor air exposure model. The detailed indoor air chemistry model was used to produce a simplified chemistry scheme for INDAIR-CHEM, which performs well for key indoor air pollutants under a ra...

An evaluation has been made of a range of simple and complex atmospheric transport models, applied to estimate sulphur and nitrogen deposition in the UK in order to provide information to policy makers to support decisions on future model use. The models were evaluated by comparison with annually averaged measurements from the national monitoring n...