The PAREMPI Project: Particle emission prevention and impact

The EU-funded PAREMPI project aims to thoroughly investigate exhaust emissions from the transport sector—not only the pollutants emitted directly from the tailpipe, but also the secondary aerosols (SecA) that form through atmospheric reactions.

Transportation is a vital part of modern life, enabling mobility and delivery of goods such as food, energy, and everyday essentials. However, there is a significant downside: these activities release a substantial amounts of greenhouse gases and air pollutants. We’re fighting the climate impact of transportation with electric vehicles, better energy efficiency, and carbon-neutral fuels, while tacking the exhaust emissions require also advanced exhaust aftertreatment systems (EATS). Yet, some transport sectors, like aviation and shipping, are difficult to electrify or equip with EATS. Additionally, current solutions focus mainly on tailpipe emissions, often ignoring how these emissions form secondary aerosols in the atmosphere.

That’s where the PAREMPI project steps in, investigating transport emissions, including secondary air pollutants and direct emissions such as gases, semivolatile compounds (SVCs), ultrafine particles (UFPs), and particulate matter (PM). Non-exhaust emissions are also on the radar. There’s a significant knowledge gap in how transport emissions contribute to secondary aerosol formation, highlighting the need for more research and ways to curb these emissions.

The PAREMPI project is building a comprehensive emissions database from existing results and new measurements, developing ePMI software to model total particulate emissions, and enhancing health impact assessments and societal cost analyses. All these efforts aim to provide solid policy recommendations from the PAREMPI consortium’s experts.

What are the secondary aerosols?

Particulate matter is a familiar component of aerosols, defined as “a mix of solid and liquid particles in the air that are small enough not to settle on the ground” (World Health Organization). Secondary aerosols are formed when aerosol and gas-phase precursor compounds from both natural and human-made sources, including transportation, are released into the atmosphere, where they interact with water, oxygen, oxidants and sunlight, leading to secondary aerosols.

The formation of secondary aerosols through atmospheric reactions is complicated due to variations in exhaust composition, the compounds and their concentrations present in the atmosphere, and the prevailing atmospheric conditions. For instance, air quality typically worsens during low winter temperatures with low mixing height, but the exact reasons, especially in relation to transport emissions, aren’t well understood. Overall, proving the role of transport emissions in ambient PM2.5 levels and their harmful effects is a challenge.

To understand the impact of the transport sectors’ tailpipe emissions on secondary aerosols, we need insights into their precursor emissions and tendency of those precursors to form secondary aerosols.

So far, the focus has been on basic emissions from transport activities, with less information on compounds like benzene, toluene, PAHs, UFPs, semivolatiles, ammonia, and the mass, composition, and toxicity of formed secondary aerosols. Emission of these varies depending on the engine, aftertreatment, and fuel technologies.

The PAREMPI project’s analysis of existing data revealed significant knowledge gaps, particularly regarding emissions under real-world conditions. The PAREMPI database, which includes 21 studies with OFR measurements of secondary aerosols from cars, heavy-duty vehicles, shipping, and aviation, showed that even for cars and HGVs, there’s limited data on emissions under real-driving conditions. For shipping, available datasets are mainly for individual ships and typically cover only some emission species. Additionally, studies focus primarily on fuels that meet the IMO’s 0.5% sulphur limit (or 3.5% sulphur limit with scrubbers), while there’s little data on LNG DF, methanol DF, and biofuels, which are increasingly used to meet the IMO’s net-zero shipping goals by 2050. For aviation, there’s a general lack of secondary aerosol emission data, especially on sustainable aviation fuels (SAF).

PAREMPI’s measurement campaigns were designed based on the recognised gaps in emission data from transport sectors.

Of the four measurement campaigns, two are complete, focusing on cars and heavy-duty trucks, and the upcoming measurements will cover marine and aviation sectors. In the first campaign, seven cars representing hybrid, diesel, gasoline, and compressed natural gas (CNG) technologies were tested at the BOSMAL research institute in Poland, with over 30 participants from various project organizations. Most cars met the Euro 6d standards, but two older cars, one gasoline and one diesel, were not equipped with particulate filters. The laboratory test cycle simulated the RDE on-road profile, while different ambient temperatures in the chassis dynamometer lab reached as low as -9 °C. For on-road car measurements, the Portable Emissions Measurement System (PEMS) was used.

In the second campaign, focusing on heavy-duty vehicle emissions with two trucks reached as far north as Lapland, gathering data on HD emissions in cold and dark winter conditions, an aspect that’s not well understood. The campaign included a new diesel truck that met the latest Euro VI E emission standard and an older Euro VI diesel truck with over a million kilometers on its odometer. Conventional diesel fuel and an aromatic-free renewable diesel were used. In the on-road heavy-duty campaign, the measuring devices were installed in a measurement container on the truck’s semi-trailer. This setup allowed for real-driving on-road measurements with a large set of instruments in a container, though it required extensive design and logistics, and presented challenges, including switching the measurement container between the two trucks.

Both PAREMPI measurement campaigns included comprehensive measurements of precursor gaseous emissions (e.g., formaldehyde, aromatics), semivolatiles, and PM emissions down to <10 nm, as well as the toxicity of exhaust. Secondary aerosol emissions form during the atmospheric aging process, lasting from minutes to weeks, so SecA can’t be directly measured. In the PAREMPI measurements, potential SecA formation was assessed using an oxidation flow reactor (OFR), where high concentrations of oxidants (O3, OH, HO2) under UV light will initiate SecA formation. The aging of diluted exhaust in the OFR has been shown to represent atmospheric aging ranging from minutes to weeks, depending on the OFR conditions. After the OFR, PN concentrations, size distributions, and aerosol compositions are measured online using tools like the Soot Particle Aerosol Mass Spectrometer (SP-AMS). The measurements with cars and trucks provide insights into emissions under various conditions, especially in cold and dark winter conditions, and the upcoming campaigns will focus on marine and aviation emissions.

Modelling and Health Impact Assessment are important tools to achieve the outcomes of the project.

The PAREMPI database and the knowledge gained from the measurements will be used to model the reactions and processes leading to the formation of health-impacting SecA from precursor emissions due to atmospheric aerosol chemistry and to predict the total PM2.5. A modeling tool, known as the ePMI software, will be developed to assess the contribution of transport emissions to the formation of ambient PM2.5 levels. With sufficient information on precursor gases, particles, and SecA emissions, combined with European-level modelling, health impact assessments and improved quantification of externalities become possible.

Not all aerosols are equally harmful, so many characteristics need to be considered, including their composition, mass, size, and number emissions. For instance, particles may carry harmful polyaromatic hydrocarbons (PAHs). Aerosols affect health by entering the respiratory system, with the smallest particles even penetrating the bloodstream, making them particularly harmful despite their low mass. Generally, transport-derived particles are small (<1 µm), while other particles, like sea salt, geological dust, and biogenic particles, tend to be larger than PM2.5. Particle emissions from cars and vehicles are limited by European emission standards, which include the number of non-volatile particles (nvPN) with a diameter above 23 nm, a limit that will tighten to 10 nm in Euro 7. However, considering the health and climate effects, total particle emissions are significant alongside the non-volatile particles, and these are included in the health impact assessment of aerosols and related external costs evaluated in the PAREMPI project. Through its scientific findings, tools, and methodologies, the PAREMPI project aims to provide solid and well-justified policy recommendations.

The PAREMPI project is supported by the European Union’s Horizon Europe research and innovation programme, and brings together some of Europe’s esteemed research organisations: VTT Technical Research Centre of Finland, the Finnish Meteorological Institute and Tampere University from Finland, BOSMAL from Poland, IEM Institute of Experimental Medicine from Czech Republic, ONERA from France, ULUND from Sweden and Magellan Circle from Portugal.