Emissions testing is an important procedure to measure and control air pollution from sources such as vehicles with combustion engines, power-plants, and other motorized equipment that produce exhaust and evaporative emissions.
Particulate matter (PM), also known as particle pollution, is the general term used to describe solid particles and liquid droplets found in the air. Once inhaled, these particles can affect the heart and lungs, and cause serious health problems. Particle classes PM10 and PM2.5 (i.e. particles with diameter less than 10 µm and 2.5 µm respectively) are carefully monitored, both at emissions sources and in the air in general, due to potential health risks.
Gravimetric analysis of PM collected via filtration is the most widely used technique for determining ambient concentrations of PM as well as the amount of PM in emissions.
Why Accurate Weighing is Important
Weighing particulate matter on filters is a differential weighing application. As the amount of particulate matter collected is very small in terms of weight, the filters must be weighed very accurately, both before and after loading of the particulate matter.
As a general rule, guidelines specify a balance with a resolution of 1 μg or 0.1 μg, with corresponding repeatability.
Weight of particulate matter collected on filters for emissions testing can be extremely low, therefore the weighing procedure has to be performed very accurately. Excellence Level microbalances with a dedicated filter weighing kit are perfect for emissions testing. The outstanding repeatability and lowest possible minimum weight provide the weighing performance you need.
Improve particulate emissions measurement accuracy with high-precision filter weighing solutions from METTLER TOLEDO.
Discover how precise gravimetric measurements help laboratories generate reliable, repeatable data while supporting readiness for evolving emissions regulations, including Euro 7 (EU 2024/1257) and other emerging global standards.
This guide provides practical insights into the role of filter weighing in modern emissions testing and highlights key considerations for maintaining measurement integrity, reducing uncertainty, and improving laboratory efficiency.
Download the guide to gain expert insights and practical recommendations for your emissions testing workflow.
The illustration above describes the process for determining the amount of particulate matter on filters gravimetrically.
Whether measuring particulate matter in exhaust gases, evaporative emissions, the atmosphere or ambient air, the gravimetric filter weighing emissions test follows the same procedure.
Clean air is recognised by the World Health Organization (WHO) as a fundamental requirement for human health and wellbeing. Around the world, increasingly stringent emissions legislation is driving the need for more sensitive, accurate, and reproducible particulate matter (PM) measurement techniques. Regulatory bodies now require emissions testing not only for traditional exhaust pollutants, but increasingly for non-exhaust emissions such as brake wear particles. This has elevated the importance of gravimetric filter weighing methods, high-performance microbalances, and accredited laboratory processes.
In the United States, emissions testing for engines and vehicles is primarily governed by US EPA 40 CFR Part 1065 – Engine-Testing Procedures, which specifies detailed requirements for particulate sampling systems, filter conditioning, weighing environments, instrument performance, calibration, and gravimetric PM analysis. In addition, 40 CFR Part 50 establishes the National Ambient Air Quality Standards (NAAQS), including the EPA PM2.5 Federal Reference Method (FRM) used for ambient air monitoring.
Within Europe, emissions and air quality monitoring are governed by a combination of legislation and standards. The recently adopted Regulation (EU) 2024/1257 (Euro 7) introduces new requirements for vehicle emissions, including brake particle emissions and tyre abrasion, while EN 12341 (published nationally as BS EN 12341 and DIN EN 12341) defines the reference gravimetric method for measuring ambient PM10 and PM2.5 concentrations.
The automotive industry remains a significant source of air pollutants including carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), particulate matter (PM), and greenhouse gases (GHGs). To demonstrate compliance, manufacturers must conduct emissions testing according to recognised international standards and regulatory procedures. These increasingly reference precise gravimetric measurement techniques (see table below) and laboratory quality systems such as ISO/IEC 17025 and ISO 14065, ensuring results are traceable, repeatable, and suitable for regulatory certification.
Gravimetric filter weighing remains the most widely accepted method for determining particulate mass. These standards define requirements for filter materials, conditioning periods, weighing-room environmental control, electrostatic neutralisation, balance performance, traceability, and quality assurance. As emissions limits continue to fall and after-treatment technologies become increasingly effective, laboratories must measure ever-smaller quantities of particulate matter with confidence and repeatability.
| Regulation / Standard | PM Measurement Application | Balance Recommendation |
| EPA 40 CFR Part 1065 | Engine and vehicle exhaust PM | Microbalance with 1 μg readability minimum; 0.1 μg preferred for ultra-low emissions and development testing. |
| EPA PM2.5 FRM | Ambient air monitoring | Analytical balance or microbalance capable of 1 μg readability; many laboratories adopt 0.1 μg systems to improve uncertainty performance. |
| EN 12341 (BS EN / DIN EN / CEN) | Ambient air monitoring (PM10 and PM2.5) | Microbalance with approximately 1 μg readability; 0.1 μg systems commonly used where lowest uncertainty is required. |
| SAE J2943 (2022) | Recommended best practice PM filter weighing | High-stability microbalance of 1 μg or better; 0.1 μg recommended for modern low-emission measurements. |
| UN GTR No. 24 | Brake emissions PM | High-performance microbalance suitable for gravimetric PM analysis; industry practice typically uses 1 μg or 0.1 μg readability. |
| Euro 7 (EU 2024/1257) | Exhaust and brake emissions | Microbalance systems capable of detecting very low particulate mass changes; typically 1 μg minimum, with 0.1 μg preferred for development and certification laboratories. |
| ISO/IEC 17025 | Laboratory accreditation | No specific readability requirement; balance must be calibrated, traceable, and capable of meeting measurement uncertainty objectives. |
Regulation (EU) 2024/1257 (Euro 7) extends emissions control beyond traditional exhaust (tailpipe) pollutants by introducing new durability requirements, enhanced real-world compliance provisions, battery durability requirements for electrified vehicles, and, for the first time, limits on non-exhaust emissions such as brake particles and tyre abrasion. While tailpipe emission limits for many pollutants remain similar to the latest Euro 6 requirements, Euro 7 significantly broadens the scope of vehicle emissions regulation and introduces lifetime compliance requirements across a much longer vehicle operating period.
New Brake Particle Emissions Requirements: Euro 7 introduces mandatory laboratory brake emissions testing based on methodologies derived from UN GTR No. 24. Vehicle manufacturers must now demonstrate compliance with brake particulate matter limits using controlled brake dynamometer testing procedures designed to represent real-world driving conditions. This is the first major global regulation to establish legally enforceable limits for brake wear particle emissions.
For more information, see our dedicated page on Euro 7 Brake Testing, covering brake dynamometer requirements, particle sampling systems, gravimetric analysis methodologies, and compliance testing strategies.
As emissions limits continue to tighten and particulate mass loading on filters decreases, laboratories increasingly require balances with readability of 1 μg or 0.1 μg. Combined with controlled environmental conditions and ISO-accredited procedures, modern ultra-microbalances provide the performance necessary to meet both current regulatory requirements and future emissions testing challenges.
Determining the weight of particulate matter is a key task in emission testing for environment control and automotive industry.
The weighing results need to be very accurate but the process itself faces a number of challenges, like influence of electrostatic charges or temperature on filters. Therefore, do not hesitate to ask for an advice! Our Expert Team is there to help you, whether you are looking to purchase a balance or need support with filter weighing/emissions testing application. Contact us and receive assistance you require.
Ideally, a cleanroom is preferable for filter weighing to avoid potential contamination from the surrounding air as well as to have more control over temperature and humidity. Alternatively, a glove box can be used but this makes the process rather cumbersome, particularly when weighing large numbers of filters. In addition, there are several other challenges associated with weighing filters:
Filter Handling
Sample Tracking
To add further process complexity, the filters must be tracked precisely. Each filter is pre-weighed, placed in a labelled holder, acclimatized, and then transported to the test site. After PM loading, filters are transported back to the lab and reweighed. Accuracy is put at risk if there is not a failsafe system in place to ensure filters are not mixed up during processing.
Weighing Accuracy
With several guidelines specifying the weighing system to be used, it is crucial that the balance used meets the needs of the filter weighing application. For such small samples, the minimum net sample weight of the balance is of critical importance – weighing a sample below this weight cannot be trusted to be of the required level of accuracy.
Time
Filter weighing for emissions testing can take a long time to complete. Acclimatization processes, transport to and from the test site, laborious handling procedures and a balance which is slow to settle contribute to a typical car exhaust emissions test taking up to 2 days or longer to finalize.
METTLER TOLEDO XPR microbalances offer unique precision and exceptionally low minimum weights. Outfitted with a special filter weighing kit and with 0.2 µg readability, the XPR2U is ideal for filter weighing and has the additional benefit of built-in active quality assurance functions to ensure weighing results meet defined tolerances and standards. Built-in user guidance ensures the differential weighing process is followed precisely.
The Right Tools
The addition of a barcode reader offers quick sample identification and the convenience to automatically match loaded filters with pre-weighed results for faster processing and fewer handling errors. Plus, passing the filters over the electrode of an AntiStatic Kit neutralizes any electrostatic charges present and ensures the true PM result is measured.
Thanks to multiple connectivity options, weighing results can be exported directly to a spreadsheet on a PC or to a company database system for inspection and further analysis.
METTLER TOLEDO tweezers are specially designed to ensure correct handling of the delicate filters as they are transferred to and from the storage cartridge and the filter weighing kit on the balance.
Watch this video to learn the main product highlights of METTLER TOLEDO's filter weighing solutions for emissions testing. Choose from innovative manual solutions using an analytical or microbalance to a fully automated solution with a robotic system, developed together with HORIBA.
METTLER TOLEDO XPR microbalances are fully compatible with LabX™ laboratory software. LabX provides full SOP user guidance on the balance. It recognizes the loading and unloading of filters, simplifying and speeding-up the process.
LabX automatically records the weight values against the correct sample IDs and performs all calculations automatically, including correction for air buoyancy.
All data and results are saved securely in a centralized database providing full traceability. Customized reports can be printed out or transferred to an internal information system.
When more than 40 filters are weighed per day, the PFS-ONE Filter Robot, in combination with the XPR2U, is the perfect automated solution.
The innovative filter holder allows identification, acclimatization, storage, transport and weighing all in one cartridge, without interruption or removal of the filter. It also acts as a Faraday Cage thereby reducing electrostatic influences.
Automated sample changing allows effortless filter pre- and back-weighing and results are immediately transferred to a PC for analysis.
If you're using large filters, for example for analyzing industrial filtrations, METTLER TOLEDO has handy and cost-effective solutions for weighing larger filters on your analytical balance. With the addition of a filter weighing kit, filters up to 110 mm can be conveniently weighed on a METTLER TOLEDO Excellence analytical balance. To weigh filters up to 150 mm, the use of a dedicated ErgoClip is recommended. Both solutions can be quickly and easily installed on your existing balance.
Firstly, the environment is important. Ideally, your balance should be located on a dedicated weighing table in a room with a stable temperature and controlled humidity. The filter weighing kits for METTLER TOLEDO microbalances and ultra-microbalances contain a special weighing pan which ensures filters are correctly placed on the balance. Correct filter handling with asymmetric tweezers will help ensure your filter weighing processes are fast and efficient.
PTFE filters are particularly prone to electrostatic charging. The unstable figures on your balance suggest that the weighing cell is being affected by electrostatic charges. The influence from electrostatic charges can significantly affect weighing results. Use an AntiStatic Kit before weighing each filter to remove any charges which may be present.
METTLER TOLEDO offers filter weighing solutions for both microbalances and for analytical balances. There are two different filter weighing kits for microbalances, enabling you to weigh filters with diameter from 20 mm to 70 mm; it's easy to switch between the kits. For weighing larger filters up to 150 mm in diameter on an analytical balance, there are two filter holder solutions available.
The METTLER TOLEDO micro filter weighing kit includes two filter pans. Each has a unique contour which ensures the filter is automatically centered. Centering the filter eliminates eccentricity errors to ensure reproducible and reliable results.
A clear SOP should be in place for weighing filters in a regulated environment. However, in a manual process, human errors can occur, and in a process which requires many steps, it can be easy to make a mistake. LabX software enables you to create your own dedicated filter weighing SOP workflow. The step-by-step instructions for the SOP are provided on the balance display. Each step requires confirmation from the user so you can be sure the SOP has been followed.
Every measurement on ANY balance is subject to uncertainty. Understanding this uncertainty is the key to ensuring accurate weighing results. It is not the readability that determines the accuracy of a weighing instrument, but rather its repeatability. With the very small sample weights involved in filter weighing, the balance's minimum net sample weight capability is also of critical importance.
To find the appropriate balance for your needs, you need to know the smallest amount you want to weigh and how accurately you need to weigh it (i.e. at what tolerance).
METTLER TOLEDO's global weighing standard, GWP® helps you choose the right balance to meet your application requirements. Ask your local representative for a free balance recommendation. Determine if your existing balance meets your quality requirements.
METTLER TOLEDO filter weighing kits have glass lids so it's easy to see what you are doing when placing and removing filters. The microbalance draft shield doors can be set to open to the left or the right according to the needs of the operator so that filter handling is more ergonomic. To speed up the process further, the SmartSens infrared sensor can be used to open the doors with the wave of a hand. For high throughput filter weighing, we recommend an automated solution with the PFS-ONE filter weighing robot.
Manual transcription of data and results carries an inherent risk of error. By connecting your balance to LabX software you can eliminate manual transcription and the associated risk of errors entirely. LabX also performs all your calculations, including air buoyancy corrections, removing a further source of potential errors. All data is saved securely in a centralized database so you benefit further from complete data integrity and traceability.
It's vitally important to label the filter cartridges and ensure that results are logged correctly against each filter. When handling many filters, this can be a challenge. The process can be greatly simplified by connecting your balance to LabX, a barcode reader and a printer. LabX prints barcoded labels automatically. By using barcodes, the samples are uniquely identified. LabX uses the barcodes to automatically log the weight results against the correct sample. All data is saved securely in a centralized database providing full traceability. The PFS-ONE filter weighing robot can process up to 1,000 filters per day in a fully automated process with all data handled automatically.
Emission refers to the release or discharge of substances (such as gases, pollutants, or radiation) directly from a source into the environment. Immission, on the other hand, refers to the presence or concentration of these substances in the environment at a particular location, often where they affect people, animals, or ecosystems. Essentially, emission is about the source output, while immission is about the impact or exposure at a receptor point.
