Aerosol Particle Number Emissions and Size Distributions: Implementation in the GAINS Model and Initial Results

Paasonen, P., Visshedjik, A., Kupiainen, K., Klimont, Z. ORCID: https://orcid.org/0000-0003-2630-198X, Denier van der Gon, H., & Kulmala, M. (2013). Aerosol Particle Number Emissions and Size Distributions: Implementation in the GAINS Model and Initial Results. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-13-020

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Abstract

Particulate matter affects our health and climate. In addition to well based knowledge on the adverse health effects related to particle mass concentrations, there is increasing evidence showing that the number concentrations of ultra-fine aerosol particles, with diameters below 0.1 um, have negative health impacts, which are significantly different from those caused by larger particles with sizes over 1 um. Particles with diameters between 0.1 and 1 um can also be activated as cloud droplets; thereby, higher number concentrations can increase the cloud albedo and thus the proportion of solar radiation reflected back to space, causing a cooling aerosol climate effect. In addition to this indirect effect, aerosol particles affect Earth radiation budget directly by either scattering solar radiation (e.g. sulphate aerosol, cooling effect) or absorbing it (black carbon aerosol, warming effect).

Currently, European air quality legislation on particulate matter is mainly focussing on particle mass, although emission standards for particle numbers have been introduced for mobile sources. Mass concentration is dominated by particles larger than 0.1 um, and it is not well associated with number concentration, due to the often different formation mechanisms of ultra-fine and larger particles. For combustion sources, some emission control technologies affect mainly large particle emissions, and may even increase emissions of ultra-fine particles. Hence, in order to comprehensively estimate health and climate effects of anthropogenic aerosol particles, it is necessary to quantify their emissions with both mass and number based metrics, including information on their size distribution.

Currently, European air quality legislation on particulate matter is mainly focussing on particle mass, although emission standards for particle numbers have been introduced for mobile sources. Mass concentration is dominated by particles larger than 0.1 um, and it is not well associated with number concentration, due to the often different formation mechanisms of ultra-fine and larger particles. For combustion sources, some emission control technologies affect mainly large particle emissions, and may even increase emissions of ultra-fine particles. Hence, in order to comprehensively estimate health and climate effects of anthropogenic aerosol particles, it is necessary to quantify their emissions with both mass and number based metrics, including information on their size distribution.

This report describes the implementation of size segregated particle number emission calculations in the GAINS model. Results show that in 2010 in Europe more than 60% of particle number emissions emerge from road transport, even though their share in total PM1 mass emissions (i.e., the mass of emitted particles with diameters below 1 um) is only 12%. Particle number emissions from road transport are expected to decrease rapidly in the future due to further tightening of exhaust emission legislation (EURO-standards). Due to the envisaged more pronounced particle number emission reduction in the road transport sector compared to the currently second and third largest source sectors, shipping and combustion of fuel wood and coal in the residential sector, emissions from the latter two sectors are anticipated to exceed road transport emissions by 2025. Estimated shares in total European emissions in 2025 range, depending on the applied future scenario, from 35 to 41% for shipping, from 26 to 29% for residential combustion and from 17 to 21% for road transport. The presented initial results are, however, subject to significant uncertainties, primarily due to limited measurement data for several emission sources.

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