Karl Ropkins

openair - An R package for air quality data analysis

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 the development of the package with the purpose of showing how air pollution data can be analysed in more insightful ways. Examples are provided of importing data from UK air pollution networks, source identification and characterisation using bivariate polar plots, quantitative trend estimates and the use of functions for model evaluation purposes. We demonstrate how air pollution data can be analysed quickly and efficiently and in an interactive way, freeing time to consider the problem at hand. One of the central themes of openair is the use of conditioning plots and analyses, which greatly enhance inference possibilities. Finally, some consideration is given to future developments.

Evaluation of worldwide approaches to the use of HACCP to control food safety

Abstract Hazard Analysis by Critical Control Point (HACCP) is a management tool, developed in the late 1960s, to ensure the safety of foods for space flights. It was subsequently recognised as an effective alternative to conventional end-point-testing by the World Health Organisation (WHO) and the United States Food and Agriculture Organisation (FAO), amongst others, and recommended for use in commercial food production. HACCP principles are now incorporated in national food safety legislation of many countries, as well as a likely future component of the standardisation of international food quality control and assurance practices. However, governments and food companies have interpreted HACCP differently. This paper describes the basic principles of HACCP, and evaluates its implementation in the European Union, North America, Australia and New Zealand, and in developing countries. The ‘Zurich House of Food-Safety’ approach was identified as the most rigorous (and possibly most effective) interpretation of HACCP, while the Australian food industry approach was identified as the most practical and readily applicable approach to HACCP.

Real-World Vehicle Exhaust Emissions Monitoring: Review and Critical Discussion

Traffic-related emissions represent a major component of airborne pollution. Historically, dynamometer testing has been most widely used to estimate vehicle emission rates, and these emission rates, in turn, have been used as inputs when modeling traffic-related air quality impacts. However, such conventional drive cycle testing is not considered strictly representative of vehicles under real driving conditions. Therefore, in recent years, significant scientific effort has been focused on the measurement and analysis of real-world vehicle emissions. Here, the use of vehicle emissions monitoring methods (e.g., in-situ methods such as tunnel, inverse dispersion, and remote sensing studies, and in-traffic measures such as probe vehicle and “car chaser” studies) to provide real-world emission estimates is reviewed and discussed in detail. Advantages and disadvantages are identified for the different vehicle emissions monitoring methods, both relative to dynamometer-based approaches and each other. Potential applications of different approaches are also discussed, with particular attention being placed on their complementary use.

Application of a Portable FTIR for Measuring On-road Emissions

The objective of this work was the development of an onroad in-vehicle emissions measurement technique utilizing a relatively new, commercial, portable Fourier Transform Infra-Red (FTIR) Spectrometer capable of identifying and measuring (at approximately 3 second intervals) up to 51 different compounds. The FTIR was installed in a medium class EURO1 spark ignition passenger vehicle in order to measure on-road emissions. The vehicle was also instrumented to allow the logging of engine speed, road speed, global position, throttle position, air-fuel ratio, air flow and fuel flow in addition to engine, exhaust and catalyst temperatures. This instrumentation allowed the calculation of massbased emissions from the volume-based concentrations measured by the FTIR. To validate the FTIR data, the instrument was used to measure emissions from an engine subjected to a real-world drive cycle using an AC dynamometer. Standard analyzers were operated simultaneously for comparison with the FTIR and the standard analyzer results showed that most pollutants (NOx, CO2, CO) were within ~10% of a standard analyzer during steady state conditions and within 20% during transients. The exception to this was total HC which was generally 50% or less than actual total HC, but this was due to the limited number of hydrocarbons measured by the FTIR. In addition to the regulated emissions, five toxic hydrocarbon species were analyzed and found to be sensitive to cold starts in varying proportions. Finally, FTIR data was compared to results from a commercially available on-road measurement system (Horiba OBS- 1000), and there was good agreement.

Using HACCP to control organic chemical hazards in food wholesale, distribution, storage and retail

HACCP (hazard analysis critical control points) is a procedure for the identification, assessment and control of hazards in, and indirectly risks from, food. Most current HACCP procedures focus on microbiological and physical hazards even though effective control requires consideration of all hazard classes (i.e., chemical, physical and microbiological hazards). To-date, the use of HACCP to control chemical hazards has been limited, particularly in auxiliary (non-production/non-manufacturing) practices. Therefore, we discuss the application of HACCP to control organic chemical contaminants of food during the wholesale, distribution, storage and retail sectors of the food supply chain, and identify practical approaches. Chemical HACCP is likely to be more effective, efficient and economical than conventional end-point-testing quality control. However, high costs of chemical monitoring will largely restrict chemical HACCP to other, less direct, control measures including safe handling practices and assured supply chains. A model wholesaler/retailer outlet was used as a framework for the development of a generic template for organic chemical contaminant HACCP procedures in the wholesale, distribution, storage and retail sectors of the food supply chain.

Quantifying temporal trends in ground level ozone concentration in the UK.

There is a high interest in quantifying temporal trends in surface ozone concentrations as they serve to quantify the impacts of the anthropogenic precursor reductions and to assess the effects of emission control strategies. In this paper ozone trends for nearly 2 decades (1993 to 2011) at both rural and urban sites have been analysed, using ground level ozone data from 5 urban and 15 rural sites, which are part of the UK AURN. This study analyses ozone trends at various percentiles, in addition to traditional mean trends using quantile regression, TheilSen function, and changepoint analysis. Ozone trends show significant variability at different statistical metrics (e.g., mean, median, maximum and selected quantiles). Maximum trends were negative, whereas median and mean trends were positive during the study period (1993-2011) at both rural and urban sites. Urban and rural trends show different rates of change and indicate that urban decrement (the difference in ozone concentration between rural and urban areas) has been decreasing over the period. Ozone trends were negative during the last 8 years (2004-2011), which could have been caused by the stabilisation of NOx concentration during this period. Furthermore, 3 changepoints were detected in the temporal trend using Pruned Exact Linear Time (PELT) search algorithm, which provides further insight into the ozone temporal trends.

Evaluation of a FTIR Emission Measurement System for Legislated Emissions Using a SI Car

A series of chassis dynamometer test trials were conducted to assess the performance of a Fourier Transform Infra Red (FTIR) system developed for on-road vehicle exhaust emissions measurements. Trials used a EURO 1 emission compliant SI passenger car which, alongside the FTIR, was instrumented to allow the routine logging of engine speed, road speed, throttle position, air-fuel ratio, air flow and fuel flow in addition to engine, exhaust and catalyst temperatures. The chassis dynamometer facility incorporated an ‘industry standard’ measurement system comprising MEXA7400 gas analyzer and CVS bag sampling which was the ‘benchmark’ for the evaluation of FTIR legislated gas-phase emissions (CO, NOx, THC and CO2) measurements. Initial steady state measurements demonstrated strong correlations for CO, NOx and THC (R2 of 0.99, 0.97 0.99, respectively) and a good correlation for CO2 (R2 = 0.92). Subsequent transient and total mass emissions measurements from replicate samplings of four different driving cycles (two standard cycles, FTP75 and NEDC, and two novel cycles based on real-world data collected in Leeds) also show good response of FTIR and satisfied agreement between the FTIR and CVS bag sampling measurements. In general, the trial results demonstrate that the on-board FTIR emission measurement system provides reliable in-journey emissions data.

HACCP in the home: a framework for improving awareness of hygiene and safe food handling with respect to chemical risk

Hazard Analysis Critical Control Points (HACCP) is a systematic approach to the identification, assessment and control of hazards. HACCP is widely accepted to be the most effective means of ensuring food safety, and HACCP principles are currently being incorporated within all commercial sectors of the food supply chain and most associated legislation. A number of potential benefits have also been identified for the application of HACCP within the domestic environment where its use has also been promoted, most notably by the World Health Organisation. One of the key components of effective commercial sector HACCP is adherence to a strict control procedure. Such a mandatory approach is not entirely feasible within the domestic sector because consumers (i) have a legal right to a safe food supply and (ii) the right to handle and prepare food as they see fit. Consequently, control measures are generally recommendatory, rather than mandatory, within the domestic sector. Therefore, the emphasis has to be placed on educating consumers, so that they can make informed decisions regarding the types of foods they buy and the procedures they employ when handling and preparing these foods for consumption. Previous published information on the use of HACCP in the domestic environment primarily focuses on microbiological hazards. However, effective HACCP requires the consideration of all hazards (i.e., chemical, microbiological and physical). Consequently, this review discusses the application of HACCP to chemical hazards in the domestic environment, using organic chemical contaminants as examples to highlight typical problems and limitations that can be encountered. Chemical HACCP procedures are likely to result in many of the advantages previously identified for microbiological HACCP procedures. For example, practical hazard control methods for the domestic sector and increased hazard awareness for consumers.

Methodology for fitting and updating predictive accident models with trend

Reliable predictive accident models (PAMs) (also referred to as Safety Performance Functions (SPFs)) have a variety of important uses in traffic safety research and practice. They are used to help identify sites in need of remedial treatment, in the design of transport schemes to assess safety implications, and to estimate the effectiveness of remedial treatments. The PAMs currently in use in the UK are now quite old; the data used in their development was gathered up to 30 years ago. Many changes have occurred over that period in road and vehicle design, in road safety campaigns and legislation, and the national accident rate has fallen substantially. It seems unlikely that these ageing models can be relied upon to provide accurate and reliable predictions of accident frequencies on the roads today. This paper addresses a number of methodological issues that arise in seeking practical and efficient ways to update PAMs, whether by re-calibration or by re-fitting. Models for accidents on rural single carriageway roads have been chosen to illustrate these issues, including the choice of distributional assumption for overdispersion, the choice of goodness of fit measures, questions of independence between observations in different years, and between links on the same scheme, the estimation of trends in the models, the uncertainty of predictions, as well as considerations about the most efficient and convenient ways to fit the required models.

Updating outdated predictive accident models

Reliable predictive accident models (PAMs) (also referred to as safety performance functions (SPFs)) are essential to design and maintain safe road networks however, ongoing changes in road and vehicle design coupled with road safety initiatives, mean that these models can quickly become dated. Unfortunately, because the fitting of sophisticated PAMs including a wide range of explanatory variables is not a trivial task, available models tend to be based on data collected many years ago and seem unlikely to give reliable estimates of current accidents. Large, expensive studies to produce new models are likely to be, at best, only a temporary solution. This paper thus seeks to develop a practical and efficient methodology to allow currently available PAMs to be updated to give unbiased estimates of accident frequencies at any point in time. Two principal issues are examined: the extent to which the temporal transferability of predictive accident models varies with model complexity; and the practicality and efficiency of two alternative updating strategies. The models used to illustrate these issues are the suites of models developed for rural dual and single carriageway roads in the UK. These are widely used in several software packages in spite of being based on data collected during the 1980s and early 1990s. It was found that increased model complexity by no means ensures better temporal transferability and that calibration of the models using a scale factor can be a practical alternative to fitting new models.