Measurements of the aerosol chemical composition and mixing state in the Po Valley using multiple spectroscopic techniques

Abstract

Abstract. The use of co-located multiple spectroscopic techniques can provide detailed information on the atmospheric processes regulating aerosol chemical composition and mixing state. So far, field campaigns heavily equipped with aerosol mass spectrometers have been carried out mainly in large conurbations and in areas directly affected by their outflow, whereas lesser efforts have been dedicated to continental areas characterized by a less dense urbanization. We present here the results obtained in San Pietro Capofiume, which is located in a sparsely inhabited sector of the Po Valley, Italy. The experiment was carried out in summer 2009 in the framework of the EUCAARI project ("European Integrated Project on Aerosol, Cloud Climate Aerosol Interaction"). For the first time in Europe, six state-of-the-art techniques were used in parallel: (1) on-line TSI aerosol time-of-flight mass spectrometer (ATOFMS), (2) on-line Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS), (3) soot particle aerosol mass spectrometer (SP-AMS), (4) on-line high resolution time-of-flight mass spectrometer-thermal desorption aerosol gas chromatograph (HR-ToFMS-TAG), (5) off-line twelve-hour resolution proton nuclear magnetic resonance (H-NMR) spectroscopy, and (6) chemical ionization mass spectrometry (CIMS) for the analysis of gas-phase precursors of secondary aerosol. Data from each aerosol spectroscopic method were analysed individually following ad-hoc tools (i.e. PMF for AMS, Art-2a for ATOFMS). The results obtained from each techniques are herein presented and compared. This allows us to clearly link the modifications in aerosol chemical composition to transitions in air mass origin and meteorological regimes. Under stagnant conditions, atmospheric stratification at night and early morning hours led to the accumulation of aerosols produced by anthropogenic sources distributed over the Po Valley plain. Such aerosols include primary components such as black carbon (BC), only partly internally mixed with secondary semivolatile compounds such as ammonium nitrate and amines. Other organic components originating from anthropogenic sources at night include monocarboxylic acids which correspond to an AMS factor analogous to the "cooking" organic aerosol (COA) already identified in urban areas. In daytime, enhanced mixing in the planetary boundary layer (PBL) along with increasing temperature determined dramatic changes in aerosol composition caused by the evaporation of semivolatile components and by the entrainment of aged aerosols transported downwards from residual layers. In other words, the entrainment of aged air masses is responsible for the accumulation of low-volatility oxygenated organic aerosol (LV-OOAs) and also for the recycling of primary species such as black carbon. The LV-OOA concentrations were shown to correlate to the simple meteorological tracers of humid PBL air produced by daytime convection over land areas. In particular, both PMF-AMS and PMF-NMR could resolve two components of LV-OOA: one from long-range transport from Central Europe, the second from recirculated PBL air from the Po Valley. According to organic aerosol source apportionment by PMF-AMS, anthropogenic aerosols accumulating in the lower layers overnight accounted for 38% of organic aerosol mass on average, another 21% was accounted for by aerosols recirculated in residual layers but still originating in North Italy, while a substantial fraction (41%) was due to the most aged aerosols imported from transalpine areas. Overall, the deployment of six state-of-the-art spectrometric techniques provided a comprehensive picture of the nature and source contributions of aerosols and aerosol precursors at a European rural site with unprecedented level of details.

On the Origin of AMS “Cooking Organic Aerosol” at a Rural Site

“…A set of other measurements are described in detail elsewhere. 21 Overall, the state-of-the-art instruments used for this analysis measure different species with different accuracy and precision, as discussed in great detail in other publications. 23−25 2.3.…”

“…PMF was applied on the hourly data obtained by the analytical techniques described above and also by the previous PMF analysis on spectroscopic data reported elsewhere. 21 The criteria adopted in this study for input data treatment, including the uncertainty matrix, and for the evaluation of the PMF solutions are discussed extensively in the Supporting Information.…”

“…This lack of knowledge needs to be filled, and the goal of this paper is to use results of a source apportionment study using six state-of-theart spectrometric techniques deployed at a rural site in the Po Valley (Italy) in 2009 to investigate the nature of the AMS COA factor. Previous work 21 provides a comprehensive picture of the nature of organic and inorganic aerosols and aerosol precursors at a European rural site with an unprecedented level of detail. Supporting Information (SI) Figure S1 shows an example of the high time resolution particle mass spectrometry instruments deployed.…”

Single-particle characterization of polycyclic aromatic hydrocarbons in background air in northern Europe

“…2b shows their respective LDI mass spectra. The labeling scheme indicates the most intense peaks and characteristic composition (see also Ault et al, 2010;Decesari et al, 2014;Dall'Osto et al, 2016a;Arndt et al, 2017).…”

Integration of Underwater Radioactivity and Acoustic Sensors into an Open Sea Near Real-Time Multi-Parametric Observation System

“…The latter parameter is measured using the RAINCAP sensor that infers the cumulate by the acoustic impact of drops on the sensing element [ 24 ]. This instrument was recently used for its reliability to monitor rainfall on both land and at sea [ 25 , 26 , 27 ].…”