Wood burning pollution in southern Chile: PM2.5 source apportionment using CMB and molecular markers☆
Graphical abstract
Introduction
Wood burning is a significant source of ambient pollution worldwide. Besides the extensive wood burning seen in developing countries (Arku et al., 2008, Gupta et al., 2012, Rai et al., 2016, Rooney et al., 2012, Stone et al., 2010, Tao et al., 2016, Yao et al., 2016), developed countries continue burning wood to heat spaces (Bari et al., 2010, Caseiro et al., 2009, Giannoni et al., 2012, Hedberg et al., 2006, Heo et al., 2013, Kumagai et al., 2010, Leithead et al., 2006, Perrone et al., 2012, Piazzalunga et al., 2011, Puxbaum et al., 2007, Ward et al., 2010). Wood burning from cook stoves and space heaters has also been identified as a relevant worldwide source of black carbon, a short-lived climate pollutant, so initiatives to reduce those sources are currently being promoted (Climate and Clean Air Coalition, 2016).
Wood burning pollution is a severe problem in southern Chile (beneath 35° S) and originated with the widespread use of wood for space heating and cooking — it was the cheapest fuel available. However, most people burn wood using inefficient stoves in households with poor thermal insulation (Schueftan and González, 2013), and they often block the stove's air inlet so that combustion slows down and particulate matter emissions rise (Jordan and Seen, 2005, Tissari et al., 2008, Hedberg et al., 2006). Fig. 1 shows annual ambient PM2.5 measured at several cities in Chile through the National System of Air Quality Information (SINCA, 2016); i.e., PM2.5 ambient concentrations (averages for 2013–2015 at a single monitoring site) are plotted against the heating degree days (HDD, a proxy of household energy demand) for each city. Southern Chilean cities have annual PM2.5 concentrations above 30 μg/m3, so around two million people are exposed to high environmental risk (MMA, 2014).
In this work, we focus on Temuco (38°44′ S, 72°36′ W), the largest mid-size city in southern Chile (population ∼ 370,000 inhabitants). Fig. 2 shows the evolution of monthly ambient PM2.5 measured at three monitoring sites across Temuco's metropolitan area since 2009 (data from Las Encinas site is also plotted in Fig. 1); specifically, the annual average is well above the World Health Organization's (WHO) guideline of 10 μg/m3 (WHO, 2005) and also exceeds Chile's national ambient air quality standard of 20 μg/m3. Ambient PM2.5 is distinctly seasonal, with higher values in the austral winter season. Temuco's contributing factors to wood smoke pollution are reasonably representative of most southern Chilean cities: a large stock of inefficient wood stoves, poor household thermal insulation and idiosyncratic wood burning practices.
According to surveys conducted in southern Chile, ∼50% of households operate woodstoves under smoldering conditions overnight, which substantially increases their emissions. Johansson et al. (2004) found that gas phase organic emissions can exceed particle phase emissions by an order of magnitude in an inefficient wood combustion process. Keller and Burtscher (2012) have estimated the ratio of secondary organic aerosols (SOA) production (in a photochemical flow reactor) to primary emissions from a cooking stove; i.e., when oxygen is not a limiting factor, the ratio varies between 0.1 and 1, suggesting that ambient SOA concentrations could be similar in magnitude to those of primary PM from wood combustion. More recently, Nalin et al. (2016) showed that organic emissions from woodstoves undergo rapid oxidation as they are diluted into atmospheric conditions, observing that increments of an order of magnitude in oxygenated PAH occur within a few seconds; afterwards, those oxygenated species may condense to the particle phase as they cool down. Winter conditions with high concentrations of organic aerosols — as recorded in southern Chile — favor the partition of volatile organic compounds towards the particle phase (Lipsky and Robinson, 2006, Donahue et al., 2013), enhancing the impact of emissions from incomplete wood burning on ambient PM concentrations.
Few studies have analyzed the chemical composition of ambient PM2.5 at Temuco. Kavouras et al. (2001) sampled ambient PM2.5 throughout 1998 in Temuco at a site close to a major street. The mean annual PM2.5 concentration was 35.3 ± 2.6 μg/m3. They applied absolute principal component analysis (APCA) and reported four factors: motor vehicles, soil, sulfur source and wood burning; their estimated contributions were 10.9, 0.0, 5.0 and 10.3 μg/m3, respectively, accounting for a total of 26.2 μg/m3. The unexplained mass, 9.1 ± 2.3 μg/m3 was ascribed to primary and secondary organic matter. Tsapakis et al. (2002) sampled 24-h ambient PM2.5 in Temuco during September 1998 (6 samples) and in Santiago (August and October 1998, 9 and 4 samples, respectively) and determined organic molecular markers using GC/MS techniques. Polycyclic aromatic hydrocarbons (PAH) concentrations were three times larger in Temuco than in Santiago, confirming that wood and coal burning emissions can significantly impact air quality. Cereceda-Balic et al. (2012) measured polycyclic aromatic hydrocarbons (PAH) in winter 2008; i.e., four 24-h samples were taken during days with high ambient PM2.5 concentrations. They found that several PAH concentration ratios were consistent with those reported in the literature for wood burning emissions.
The purpose of this work is to identify and estimate sources of ambient organic carbon (OC) and PM2.5 in Temuco by using molecular markers characteristic of different emission sources (diesel and gasoline vehicles, wood burning, oil and coal combustion, vegetation debris, etc.). This technique has been widely used to apportion ambient OC and PM2.5 worldwide (Daher et al., 2011, Hamad et al., 2015, Subramanian et al., 2007; E. Stone et al., 2010); to our knowledge, this is the very first time that this technique has been applied in an urban area with severe wood smoke pollution in southern Chile.
In the next sections of this manuscript, we describe our methodology and ambient monitoring campaign, report the results obtained for chemical speciation and source apportionment of OC and PM2.5 and discuss the relevance of these results for other cities in southern Chile, including policy implementation issues.
Section snippets
Sampling site and method
The sampling site was a soccer stadium located in a residential area, roughly 700 m northwest of a continuous monitor belonging to the network operated by the Ministry of the Environment (Supplementary Fig. 1). The site is surrounded by a residential zone and away from major traffic routes. We conducted the monitoring campaign during the winter season, when ambient PM2.5 is highest (see Fig. 2).
The campaign lasted 10 weeks, from July 10th to September 17th, 2014; during this winter period,
Features of ambient PM2.5 at Temuco
Temuco has three air quality monitoring sites within the urban area: Las Encinas (LE), Museo Ferroviario (MF) and Padre Las Casas (PLC); all ambient monitors are within 5 km of each other and within the urban area (Supplementary Fig. 1). We used the Wilcoxon rank test (Hollander and Wolfe, 1999) to test for significant differences among paired station data; the null hypothesis was that both data sets would have the same median. The results show that there were significantly higher median values
Conclusions
For the very first time, a molecular marker source apportionment of ambient OC and PM2.5 was conducted in Temuco, a mid-size city representative of serious wood smoke pollution in southern Chile. Primary resolved sources were wood smoke (37.5%), coal combustion (4.4%), diesel vehicles (3.3%), dust (2.2%) and vegetative detritus (0.7%); secondary inorganic PM2.5 (sulfates, nitrates and ammonium) contributed with 4.8% and unresolved (“other”) organic aerosols contributed with 47.1%. The
Acknowledgements
FB was supported by Centro de Ciencia del Clima y la Resiliencia (CR2, www.cr2.cl), Grant CONICYT/FONDAP/15110009. HJ was supported by Centro de Desarrollo Urbano Sustentable (CEDEUS, www.cedeus.cl), Grant CONICYT/FONDAP/15110020.
References (74)
- et al.
Characterizing air pollution in two low-income neighborhoods in Accra, Ghana
Sci. Total Environ.
(2008) - et al.
Temporal variation and impact of wood smoke pollution on a residential area in southern Germany
Atmos. Environ.
(2010) - et al.
Wood burning impact on PM10 in three Austrian regions
Atmos. Environ.
(2009) - et al.
Characterization, sources and redox activity of fine and coarse particulate matter in Milan, Italy
Atmos. Environ.
(2012) - et al.
The use of levoglucosan for tracing biomass burning in PM2.5 samples in Tuscany (Italy)
Environ. Pollut.
(2012) - et al.
Source apportionment of PM2.5 carbonaceous aerosol in Baghdad, Iraq
Atmos. Res.
(2015) - et al.
Source apportionments of PM2.5 organic carbon using molecular marker positive matrix factorization and comparison of results from different receptor models
Atmos. Environ.
(2013) - et al.
Keeping the home fires burning: the affect heuristic and wood smoke pollution
J. Environ. Psychol.
(2007) - et al.
Chemical characterisation of PM2.5, PM10 and coarse particles at urban, near-city and rural sites in Switzerland
Atmos. Environ.
(2005) - et al.
Emission characteristics of modern and old-type residential boilers fired with wood logs and wood pellets
Atmos. Environ.
(2004)
A continuous photo-oxidation flow reactor for a defined measurement of the SOA formation potential of wood burning emissions
J. Aerosol Sci.
Levoglucosan and dehydroabietic acid: evidence of biomass burning impact on aerosols in the lower fraser valley
Atmos. Environ.
Fast oxidation processes from emission to ambient air introduction of aerosol emitted by residential log wood stoves
Atmos. Environ.
Identification and emission rates of molecular tracers in coal smoke particulate matter
Fuel
Size distribution of water-soluble components in particulate matter emitted from biomass burning
Atmos. Environ.
Sources of high PM2.5 concentrations in milan, northern Italy: molecular marker data and CMB modelling
Sci. Total Environ.
Estimates of wood burning contribution to PM by the macro-tracer method using tailored emission factors
Atmos. Environ.
Assessing polycyclic aromatic hydrocarbons (PAHs) using passive air sampling in the atmosphere of one of the most wood-smoke-polluted cities in Chile: the case study of Temuco
Chemosphere
Composition and source apportionment of PM1 at urban site Kanpur in India using PMF coupled with CBPF
Atmos. Res.
Atmospheric polycyclic aromatic hydrocarbons: source attribution, emission factors and regulation
Atmos. Environ.
‘This is not a burning issue for me’: how citizens justify their use of wood heaters in a city with a severe air pollution problem
Energy Policy
Spatial and temporal patterns of particulate matter sources and pollution in four communities in Accra, Ghana
Sci. Total Environ.
Source apportionment of airborne particulate matter using organic compounds as tracers
Atmos. Environ.
Reduction of firewood consumption by households in south-Central Chile associated with energy efficiency programs
Energy Policy
Chemical composition of particles from traditional burning of pakistani wood species
Atmos. Environ.
Sensitivity of molecular marker-based CMB models to biomass burning source profiles
Atmos. Environ.
Sources of organic aerosol: positive matrix factorization of molecular marker data and comparison of results from different source apportionment models
Atmos. Environ.
Levoglucosan, a tracer for cellulose in biomass burning and atmospheric particles
Atmos. Environ.
Chemical characterization and source apportionment of fine and coarse particulate matter in Lahore, Pakistan
Atmos. Environ.
“Insights into the primary-secondary and regional-local contributions to organic aerosol and PM2.5 mass in Pittsburgh, Pennsylvania
Atmos. Environ.
Uncertainty assessment of source attribution of PM2.5 and its water-soluble organic carbon content using different biomass burning tracers in positive matrix factorization analysis – a case study in Beijing, China
Sci. Total Environ.
Fine particle and gaseous emissions from normal and smouldering wood combustion in a conventional masonry heater
Atmos. Environ.
The composition and sources of PM 2. 5 organic aerosol in two urban areas of Chile
Atmos. Environ.
A common representative intermediates (CRI) mechanism for VOC degradation. Part 3: development of a secondary organic aerosol module
Atmos. Environ.
Chemical speciation and source apportionment of fine particulate matter in Santiago, Chile, 2013
Sci. Total Environ.
The effective variance weighting for least squares calculations applied to the mass balance receptor model
Atmos. Environ. (1967)
Sources apportionment of PM2.5 in a background site in the north China plain
Sci. Total Environ.
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This paper has been recommended for acceptance by David Carpenter.