A study on the relationship between mass concentrations, chemistry and number size distribution of urban fine aerosols in Milan, Barcelona and London

Abstract

Abstract.A physicochemical characterization, including aerosol number size distribution, chemical composition and mass concentrations, of the urban fine aerosol captured in MILAN, BARCELONA and LONDON is presented in this article. The objective is to obtain a comprehensive picture of the microphysical processes involved in aerosol dynamics during the: 1) regular evolution of the urban aerosol (daily, weekly and seasonal basis) and in the day-to-day variations (from clean-air to pollution-events), and 2) the link between "aerosol chemistry and mass concentrations" with the "number size distribution".The mass concentrations of the fine PM 2.5 aerosol exhibit a high correlation with the number concentration of >100 nm particles N>100 (nm) ("accumulation mode particles") which only account for <20% of the total number concentration N of fine aerosols; but do not correlate with the number of <100 nm particles ("ultrafine particles"), which accounts for >80% of fine particles number concentration. Organic matter and black-carbon are the only aerosol components showing a significant correlation with the ultrafine particles, attributed to vehicles exhausts emissions; whereas ammonium-nitrate, ammonium-sulphate and also organic matter and black-carbon correlate with N>100 (nm) and attributed to condensation mechanisms, other parCorrespondence to: S. Rodríguez (srodriguez@inm.es) ticle growth processes and some primary emissions. Time series of the aerosol DpN diameter (dN/dlogD mode), mass PM 2.5 concentrations and number N>100 (nm) concentrations exhibit correlated day-to-day variations, which point to a significant involvement of condensation of semi-volatile compounds during urban pollution events. This agrees with the observation that ammonium-nitrate is the component exhibiting the highest increases from mid-to-high pollution episodes, when the highest DpN increases are observed. The results indicates that "fine PM 2.5 particles urban pollution events" tend to occur when condensation processes have made particles grow large enough to produce significant number concentrations of N>100 (nm) ("accumulation mode particles"). In contrast, because the low contribution of ultrafine particles to the fine aerosol mass concentrations, high "ultrafine particles N<100(nm) events" frequently occurs under low PM 2.5 conditions. The results of this study demonstrate that vehicles exhausts emissions are strongly involved in this ultrafine particles aerosol pollution.

Exploration of PM&lt;sub&gt;2.5&lt;/sub&gt; sources on the regional scale in the Pearl River Delta based on ME-2 modeling

“…Compared with the PM 2.5 concentrations reported by other cities in China in recent years, the PM 2.5 concentrations in urban Guangzhou and Shenzhen in this study were 39 %-63 % lower than those in Beijing ( 41) HS (47) DM (35) QA (37) UT (37) DP (28 in northern China, Shanghai (Ming et al, 2017) in eastern China, and Chengdu in western China. However, the PM 2.5 concentrations in urban Guangzhou and Shenzhen observed in this study were clearly higher than those in famous megacities in developed countries, such as Paris (Bressi et al, 2013), London (Rodríguez et al, 2007) and Los Angeles (Hasheminassab et al, 2014), while they were similar to those of Santiago (Villalobos et al, 2015) and Chuncheon (Cho et al, 2016). It should be highlighted that the higher concentration of SO 2− 4 in the urban atmosphere of the PRD is one of the major reasons leading to the higher degree of PM 2.5 pollution in the PRD compared to that in developed cities.…”

Transport impacts on atmosphere and climate: Land transport

“…The total particle number measured in urban areas often correlates well with NO x and shows a distinct diurnal variation, indicating a common traffic source (Ketzel et al, 2004;Hussein et al, 2004). Traffic emissions are able to affect submicron particle number concentrations around major roads and may be a dominant source of ultrafine particles (PM 0.1 ) in the urban atmosphere (Despiau and Croci, 2007;Rodriguez et al, 2007). For example, 1 h after a traffic peak at street level significant increases (bursts) in concentrations of particles around 30 nm have been reported.…”

Source apportionment of fine PM and sub-micron particle number concentrations at a regional background site in the western Mediterranean: a 2.5 year study

“…Despite this fact, the fine PM fraction and its chemical composition remain relatively understudied, especially outside urban areas. In recent years much attention has been focused on the aerosol sub-micron particle number concentration, which has been shown to have an inverse relationship with mass (Rodríguez et al, 2007;Pey et al, 2008). This implies that a reduction of ambient PM concentrations, as encouraged by pollution abatement strategies, might actually increase sub-micrometer particle number concentrations.…”