The influence of particle composition upon the evolution of urban ultrafine diesel particles on the neighbourhood scale

Research output: Contribution to journalArticle

External organisations

  • King Abdulaziz University

Abstract

A recent study demonstrated that diesel particles in urban air undergo evaporative shrinkage when advected to a cleaner atmosphere (Harrison et al., 2016). We explore, in a structured and systematic way, the sensitivity of nucleation-mode diesel particles (diameter&thinsp; classCombining double low line"inline-formula"&lt;&thinsp;30&thinsp;nm) to changes in particle composition, saturation vapour pressure, and the mass accommodation coefficient. We use a multicomponent aerosol microphysics model based on surrogate molecule ( classCombining double low line"inline-formula"C16ĝ'C32 classCombining double low line"inline-formula"<in</i-alkane) volatilities. For standard atmospheric conditions (298&thinsp;K, 1013.25&thinsp;hPa), and over timescales (ca. 100&thinsp;s) relevant for dispersion on the neighbourhood scale (up to 1&thinsp;km), the choice of a particular vapour pressure dataset changes the range of compounds that are appreciably volatile by two to six carbon numbers. The nucleation-mode peak diameter, after 100&thinsp;s of model runtime, is sensitive to the vapour pressure parameterisations for particles with compositions centred on surrogate molecules between classCombining double low line"inline-formula"C22H46 and classCombining double low line"inline-formula"C24H50. The vapour pressure range, derived from published data, is between 9.23&thinsp; classCombining double low line"inline-formula"×&thinsp;10 classCombining double low line"inline-formula"ĝ'3 and 8.94&thinsp; classCombining double low line"inline-formula"×&thinsp;10 classCombining double low line"inline-formula"ĝ'6 Pa for classCombining double low line"inline-formula"C22H46 and between 2.26&thinsp; classCombining double low line"inline-formula"×&thinsp;10 classCombining double low line"inline-formula"ĝ'3 and 2.46&thinsp; classCombining double low line"inline-formula"×&thinsp;10 classCombining double low line"inline-formula"ĝ'7 Pa for classCombining double low line"inline-formula"C24H50. Therefore, the vapour pressures of components in this range are critical for the modelling of nucleation-mode aerosol dynamics on the neighbourhood scale and need to be better constrained. Laboratory studies have shown this carbon number fraction to derive predominantly from engine lubricating oil. The accuracy of vapour pressure data for other (more and less volatile) components from laboratory experiments is less critical. The influence of a core of non-volatile material is also considered; non-volatile core fractions of more than 5&thinsp;% are inconsistent with the field measurements that we test the model against. We consider mass accommodation coefficient values less than unity and find that model runs with more volatile vapour pressure parameterisations and lower accommodation coefficients are similar to runs with less volatile vapour pressure parameterisations and higher accommodation coefficients. The new findings of this study may also be used to identify semi-volatile organic compound (SVOC) compositions that play dominating roles in the evaporative shrinkage of the nucleation mode observed in field measurements (Dall'Osto et al., 2011).</p.

Details

Original languageEnglish
Pages (from-to)17143-17155
Number of pages13
JournalAtmospheric Chemistry and Physics
Volume18
Issue number23
Publication statusPublished - 5 Dec 2018

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