Abstract
Abstract. Atmospheric organic aerosols are generally classified as primary and secondary (POA and SOA) according to their formation processes. An actual separation, however, is challenging when the timescales of emission and gas-to-particle formation overlap. The presence of SOA formation in biomass burning plumes leads to scientific questions about whether the oxidized fraction of biomass burning aerosol is rather of secondary or primary origin, as some studies would suggest, and about the chemical compositions of oxidized biomass burning POA and SOA. In this study, we apply nuclear magnetic resonance (NMR) spectroscopy to investigate the functional group composition of fresh and aged biomass burning aerosols during an intensive field campaign in the Po Valley, Italy. The campaign was part of the EUCAARI project and was held at the rural station of San Pietro Capofiume in spring 2008. Factor analysis applied to the set of NMR spectra was used to apportion the wood burning contribution and other organic carbon (OC) source contributions, including aliphatic amines. Our NMR results, referred to the polar, water-soluble fraction of OC, show that fresh wood burning particles are composed of polyols and aromatic compounds, with a sharp resemblance to wood burning POA produced in wood stoves, while aged samples are clearly depleted of alcohols and are enriched in aliphatic acids with a smaller contribution of aromatic compounds. The comparison with biomass burning organic aerosols (BBOA) determined by high-resolution aerosol mass spectrometry (HR-TOF-AMS) at the site shows only a partial overlap between NMR BB-POA and AMS BBOA, which can be explained by either the inability of BBOA to capture all BB-POA composition, especially the alcohol fraction, or the fact that BBOA account for insoluble organic compounds unmeasured by the NMR. Therefore, an unambiguous composition for biomass burning POA could not be derived from this study, with NMR analysis indicating a higher O / C ratio compared to that measured for AMS BBOA. The comparison between the two techniques substantially improves when adding factors tracing possible contributions from biomass burning SOA, showing that the operational definitions of biomass burning organic aerosols are more consistent between techniques when including more factors tracing chemical classes over a range of oxidation levels. Overall, the non-fossil total carbon fraction was 50–57%, depending on the assumptions about the 14C content of non-fossil carbon, and the fraction of organic carbon estimated to be oxidized organic aerosol (OOA) from HR-TOF-AMS measurements was 73–100% modern.
Highlights
The adoption of new regulatory actions for reducing the emissions from fossil fuel combustion have certainly contributed to measurable decreases in atmospheric particulate matter concentrations in several areas in North America and Europe in the last two decades (Barmpadimos et al, 2011, 2012; Hand et al 2012)
The evaluation of abatement strategies for the organic fraction of particulate matter is challenging due to the number of anthropogenic and natural sources contributing to organic aerosol (OA) and to the complexity of the atmospheric processes controlling the concentrations of organic compounds susceptible to partitioning from the gas to the aerosol phase
On 9 and 10 April, ten stations showed concentrations above 40 μg m−3. These kinds of pollution events extending over an entire sector of the Po Valley provide an example of how distributed pollution sources associated with a particular orography and under stagnant meteorological conditions lead to regional pollution events characterized by small differences in aerosol loadings between urban and rural environments
Summary
The adoption of new regulatory actions for reducing the emissions from fossil fuel combustion have certainly contributed to measurable decreases in atmospheric particulate matter concentrations in several areas in North America and Europe in the last two decades (Barmpadimos et al, 2011, 2012; Hand et al 2012). Relevant for the present study, are (a) the fact that a large fraction of modern carbon is found in OC, even in environments highly impacted by fossil fuel combustion (Hodzic et al 2010); (b) the importance of residential biofuel combustion emissions worldwide, including industrialized countries (Bond et al, 2004; Kulmala et al, 2011); and (c) the fact that the budget of the OC emitted by combustion sources often includes a non-negligible fraction of secondary origin, i.e., forming in the plume by secondary reactions (Robinson et al 2007; Nordin et al, 2013) These findings suggest that the presence of primary and secondary organic aerosol (respectively, POA and SOA) from biomass burning is much more significant than was believed in the past, and perhaps up to 30 % of the global aerosol OC budget (Hallquist et al, 2009). We compare the spectral fingerprints of wood burning aerosol as determined by HR-TOF-AMS and 1H-NMR spectroscopies during the 2008 EUCAARI experiment in the Po Valley, and we interpret the chemical composition of NMR-determined biomass burning aerosol on the basis of laboratory and field data obtained in past and parallel experiments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
