Chemical characterization of submicron regional background aerosols in the western Mediterranean using an Aerosol Chemical Speciation Monitor

M C Minguillón,F Canonaco,A Alastuey,A Ripoll,N Pérez,A S H Prévôt,X Querol

doi:10.5194/acp-15-6379-2015

Abstract

Abstract. An Aerosol Chemical Speciation Monitor (ACSM, Aerodyne Research Inc.) was deployed at the Montseny (MSY; 41° 46'46" N, 02° 21'29" E, 720 m a.s.l.) regional background site in the western Mediterranean, Spain, from June 2012 to July 2013 to measure real-time inorganic (nitrate, sulfate, ammonium and chloride) and organic submicron aerosol concentrations. Co-located measurements, including real-time submicron particulate matter (PM1) and black carbon (BC) concentrations, and off-line PM1 chemical analysis were also carried out. This is one of the few studies that compare ACSM data with off-line PM1 measurements, avoiding the tail of the coarse mode included in the PM2.5 fraction. The ACSM + BC concentrations agreed with the PM1 measurements, and a strong correlation was found between the concentrations of ACSM species and the off-line measurements, although some discrepancies remain unexplained. Results point to a current underestimation of the relative ionization efficiency (RIE) established for organic aerosol (OA), which should be revised in the future. The OA was the major component of submicron aerosol (53% of PM1), with a higher contribution in summer (58% of PM1) than in winter (45% of PM1). Source apportionment of OA was carried out by applying positive matrix factorization (PMF), using the multilinear engine (ME-2) to the organic mass spectral data matrix. Three sources were identified in summer: hydrocarbon-like OA (HOA), low-volatile oxygenated OA (LV-OOA), and semi-volatile oxygenated OA (SV-OOA). The secondary OA (SOA; 4.8 μg m−3, sum of LV-OOA and SV-OOA) accounted for 85% of the total OA, and its formation during daytime (mainly SV-OOA) was estimated to be 1.1 μg m−3. In winter, HOA was also identified (12% of OA), a contribution from biomass burning OA (BBOA) was included and it was not possible to differentiate between two different SOA factors, but a single oxygenated OA (OOA) factor was resolved. The OOA contribution represented 60% of the total OA, with a degree of oxidation higher than both OOA summer factors. An intense wildfire episode was studied, obtaining a region-specific BBOA profile.

Highlights

Ambient aerosols have adverse effects on human health (Pope III and Dockery, 2006) and affect climate (IPCC, 2013), ecosystems, crops and regional visibility
The present study aims at interpreting a 1-year time series of inorganic and organic compounds in the submicron aerosol in the regional western Mediterranean basin (WMB), with a special focus on their evolution throughout the year as a function of the concatenation of different atmospheric scenarios
The sum of the Aerosol Chemical Speciation Monitor (ACSM) component concentrations and the black carbon (BC) concentrations measured by the MAAP was compared with PM1 concentrations determined by the optical particle counter, resulting in a strong correlation and a slope very close to unity (1.005) (Fig. 1)

Summary

Introduction

Ambient aerosols have adverse effects on human health (Pope III and Dockery, 2006) and affect climate (IPCC, 2013), ecosystems, crops and regional visibility. The chemical composition of PM2.5 is characterized by high concentrations of organic aerosol and sulfate, followed by crustal material, nitrate and ammonia, with sea spray and elemental carbon being a minor part of the total PM2.5 mass (Cusack et al, 2012). Compared to other central European sites, the western Mediterranean aerosol is characterized by higher concentrations of crustal material but lower concentrations of organic aerosol, elemental carbon and ammonium nitrate (Pey et al, 2009). Relatively high PM2.5 concentrations of carbonaceous aerosol and sulfate transported from populated coastal areas are regularly recorded, especially during winter anticyclonic episodes and summer midday PM highs (Pey et al, 2009, 2010). The organic carbon (OC) to EC ratio found (14 in summer, 10 in winter) pointed to the influence of biogenic emissions, secondary organic aerosol (SOA) formation favoured by high ozone concentrations and insolation, and the intensive recirculation of aged air masses (Pey et al, 2009; Querol et al, 2013)

Methods

Results

Conclusion