What problems to diesel machines cause for air quality? European air pollution rules for off-road diesel machines such as bulldozers, excavators and barges are much more lax than those for cars and lorries. As well as this, some engine types (for example, diesel locomotives) and older machines are excluded from air quality laws. This is a problem because, according to the World Health Organisation (WHO), diesel exhaust is carcinogenic. Diesel machines account for 12% of nitrogen dioxide (NOx) emissions and 15% of fine particles from land-based sources but their importance is increasing as emissions from other land sources are reduced due to more stringent emissions legislation. In 2016 Europe updated the relevant legislation but, despite making some improvements, lawmakers failed to harmonise the standards with those for lorry engines – currently the most closely comparable road vehicle in terms of emissions and engine configuration. In order to substantially reduce emissions that harm both human health and the environment, the EU should act soon. Why is particulate matter a problem for diesel machines? Particulate matter (PM) is the general term used to describe a mixture of suspended particles in the air. They are classified according to their diameter. Ultrafine particles are the most dangerous as they can penetrate deep into the lungs, enter the bloodstream and even reach the brain. Historically, Europe has measured and regulated PM by the total weight. Unsurprisingly, this approach has led road-vehicle and diesel machinery manufacturers to focus on reducing the bigger and heavier PM while ignoring the smaller and more dangerous ones. In recent years, Europe has also started to regulate the number of particulates, known as particulate matter number (PN). Regulating PM and PN ensures that both large and small particles are cut. In the latest reform, Europe has finally applied this new parameter to most engines for diesel machines, requiring them to fit particulate traps after 2020. However, some important categories, such as diesel locomotives used for freight operations, are exempt from the new rules. Ultrafine particles are therefore still a major problem for those trains, still used regularly in many parts of Europe. Why is NOx a problem in diesel machinery? For some diesel machinery, nitrogen oxide (NOx) emissions limits are much higher than those for the equivalent road vehicles. Road vehicles are now equipped with catalysts, which treat and reduce these emissions in the exhaust gas. In contrast, some road machinery and barge standards for NOx are so lax they can be met without any exhaust after-treatment. The latest reform failed to significantly improve NOx standards for new diesel machines, leaving this to a future review in 2023. This is a missed opportunity as technology to cut such pollution is available and already widely used in other applications such as trucks and buses. Find out how ovulation works in this very useful article on women's health, and understand the science behind how to conceive faster with this useful online resource. What should Europe do about the impact of diesel machines on air quality? Future legislation concerning diesel machines should: Align, wherever possible, standards for diesel machines to those for road vehicles. In particular, this means bringing down the currently weak NOx standards in line with best practice and WHO air quality guidelines. Enlarge the scope of the legislation to cover excluded machines: diesel machines with engines above 560 kW and below 19kW and diesel locomotives. Address emissions from existing machines. Diesel machines have a long lifetime and, without retrofitting of catalysts, will continue to pollute for a long time. Exemptions and flexibilities should be cut drastically so that it is impossible to sell machinery-equipped engines which comply with an old standard after a limited time from when the standard enters force. Finalise, no later than 2017, new provision on real-world testing of diesel machines (such as in-service surveillance) to make sure that these machinery meet air pollution standards when operated in real life (not only in lab testing). Transparency should be ensured by mandatory publication of an engine’s emissions performance in a publicly available European database.