Measurement report: Fourteen months of real-time characterisation of the submicronic aerosol and its atmospheric dynamics at the Marseille–Longchamp supersite

Abstract

Abstract. This study reports results of PM1 chemical composition determined using a Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) over a 14-month period (1 February 2017–13 April 2018) at the Marseille–Longchamp supersite (MRS-LCP) in France. Parallel measurements were performed with an aethalometer, an ultrafine particle monitor and a suite of instruments to monitor regulated pollutants (PM2.5, PM10, NOx, O3 and SO2). The average PM1 chemical composition over the period was dominated by organic aerosol (OA; 49.7 %) and black carbon (BC; 17.1 %), while sulfate accounted for 14.6 %, nitrate for 10.2 %, ammonium for 7.9 % and chloride for 0.5 % only. Wintertime was found to be the season contributing the most to the annual PM1 mass concentration (30 %), followed by autumn (26 %), summer (24 %) and spring (20 %). During this season, OA and BC concentrations were found to contribute 32 % and 31 % of their annual concentrations, respectively, as a combined result of heavy urban traffic, high emissions from residential heating and low planetary boundary layer (PBL) height. Most (75 %) of the 15 days exceeding the target daily PM2.5 concentration value recommended by the World Health Organization (WHO) occurred during this season. Local and long-range pollution episodes with contrasting chemical composition could be distinguished, accounting for 40 % and 60 % of the exceedance days, respectively. Enhanced OA and BC concentrations, mostly originating from domestic wood burning under nocturnal land breeze conditions, were observed during local pollution episodes, while high levels of oxygenated OA and inorganic nitrate were associated with medium-/long-range transported particles. In summertime, substantially higher concentrations of sulfate were found, with an average and a maximum contribution to the PM1 mass of 24 % and 66 %, respectively. Results from k-means clustering analysis of daily profiles of sulfate concentrations clearly reveal the significant influence of local harbour/industrial activities on air quality in addition to the more regional contribution of shipping traffic that originates from the Mediterranean basin.

Online Chemical Characterization and Sources of Submicron Aerosol in the Major Mediterranean Port City of Piraeus, Greece

“…This pattern can be more readily understood by the comparison with wind plots of NO x (enhancement for low winds of the northeast sector, twice a day) and SO 2 (an indicator of shipping emissions, presenting large enhancements for flows from the port sector to the west, which intensify around midday [94]). The patterns observed for BC ff and NO x , with wind-dependence indicative of traffic, port activity and residential heating, were reproduced also by OA [35].…”

“…This comes in contrast to the seasonal pattern at THI, where BC ff levels declined significantly (20%, p < 0.01). Such seasonal homogeneity is not frequently observed for BC ff in European cities [113], but can be occasionally seen at traffic sites [114] and sites in port areas [35].…”

“…While the nighttime peak is known to be related to the fast processing of BB emissions [25,49], the morning peak trailed that of BC ff by two hours and was much more distinct than the small morning hump observed at THI in the past [49]. This provides an indication of local nitrate production through the fast atmospheric conversion of NO x emissions, most likely co-emitted with ammonia by vehicles [35], in the cool winter conditions that prevent evaporative losses [103]. Nitrate was correlated well with the ammonium ion (r 2 = 0.62), with BC bb especially in nighttime (r 2 = 0.69; Figure S8b) and more modestly with BC ff and NO x during the daytime (r 2 : 0.36, 0.37, respectively; Figure S8a).…”

“…However, these levels were substantially higher than those reported at the urban background THI site in Athens during past summers (5.4 µg m −3 ) [49], justifying a measurable input from local sources. The summertime diurnal cycle of OA (Figure 2b) was mostly flat [35,81], with hourly means varying between 6-8 µg m −3 and only a minor hump around the morning rush hour (this was also present in the mean weekday cycle, but not at weekends). This variability pattern is attributed to the combination of local sources with photochemically formed and regionally transported organic particles, since the summertime levels of the latter in the GAA are known to peak during midday and afternoon [108].…”

“…Their results are useful for determining aerosol types and source contributions on a long-term basis, but do not often provide detailed information on emission patterns of sources that induce short-term variations, and this limits their applicability in designing intervention policies. Online chemical composition measurements (coupled with source apportionment in high resolution) can address this need, but such results are not abundant in the case of port cities, especially in the Mediterranean [34,35]. Various studies using aerosol mass spectrometry near major ports noted the potential effect of shipping emissions.…”