Vehicle exhaust emissions

In modern cities, vehicle exhaust is considered a major source of air pollution. Internal combustion engines in cars, aeroplanes, ships and power stations emit numerous air pollutants, which have been shown to have a variety of harmful effects on public health and the natural environment.

The real-time analysis of vehicle exhaust—monitoring the exhaust gases emitted by internal combustion engines, which contain a large number of compounds with rapidly changing concentrations—is a task for which mass spectrometers are well-suited.

In addition to emissions of carbon monoxide (CO), nitrogen oxides (NOx), particulate matter and sulphur oxides (SOx), the emissions from internal combustion engines also include volatile organic compounds (VOCs) and their photochemical reaction products in the atmosphere, the hazards of which to public health are a major cause for concern.

Real-time (or on-line) analysis is required during the initial cold start phase of a vehicle or the idling phase of an aircraft engine—which account for the majority of emitted compounds—as well as during periods of rapid acceleration. Analysing the composition of the exhaust gases enables investigation into which processes and parameters lead to these emissions.

The ProC-TOF online mass spectrometer system is a highly sensitive, real-time quantitative analysis technique for hydrocarbons and VOCs. The ability to monitor emissions in real time is particularly useful for studying rapidly changing conditions during combustion and for evaluating the impact of control technologies. The on-site (real-time) capability of online mass spectrometry, combined with efficient and soft ionisation, provides additional advantages for vehicle exhaust monitoring. The mass spectrometer plays the following roles:

Emission rates vary rapidly with engine operating conditions, thus requiring high-resolution measurements

Compared with offline methods, real-time analysis allows for the measurement of compounds that are subject to change. For example, acrolein is an unstable compound that is easily lost during the offline sampling process.

High sensitivity and good separation of isomeric compounds.

Online mass spectrometers are also valuable tools for the study of emissions from other fuels

For diesel engine exhaust, On-Board Diagnostics (OBD) signals are used to monitor vehicle parameters. By combining OBD data with measurements from the ProC-TOF online mass spectrometer, various emissions VOCs (e.g. acrolein, ethanol, styrene, formaldehyde, acetone, ethylbenzene, benzene, acetaldehyde, xylene, trimethylbenzene, 1,3-butadiene, toluene and naphthalene)

For petrol and petrol-ethanol blends, petrol is typically blended with ethanol, for example E10 (10 per cent ethanol added to 90 per cent petrol). When analysing exhaust emissions, online mass spectrometers such as these real-time instruments are powerful tools for revealing the relationship between emissions and vehicle parameters.

At the same time, the ProC-TOF online mass spectrometer can also monitor catalytic desulphurisation and denitrification of coal-fired flue gases.