Primary and secondary emissions of pellets and logwood residential heating appliances: emissions factors, secondary aerosol formation potential and chemical characterization
Résumé
To decrease the dependence on fossil fuels and to limit
global warming, the use of renewable energy has
significantly increased over the last decade in Europe.
Biomass energy has been largely promoted for
residential heating due to its (almost) neutrality
concerning CO2 emissions. However, residential wood
combustion accounts for an important source of air
pollution as it emits large quantities of fine particulate
matter (PM2.5), black carbon (BC) and volatile and semivolatile
organic compounds (VOCs and SVOCs) that are
precursors of secondary organic aerosol (SOA). The
quantity and composition of the emissions vary largely
according to the appliance, the fuel used and the
operating conditions. In particular, pellets appliances
are an interesting alternative to logwood ones due to
their lower primary emissions of PM2.5 and organic
gaseous compounds (Olsen et al., 2020). To date, only
limited information is available on the secondary
aerosol formation from pellets residential heating
appliances while several studies have shown the high
SOA formation potential from logwood stoves emissions
(Bertrand et al., 2017; Heringa et al., 2012). It is
therefore urgent to evaluate the secondary emissions of
pellet devices as well as primary PM and BC emissions in
order to assess their impact on air quality. The aims of
this study are to determine the emission factors of
primary pollutants and secondary aerosol formation
potential of pellets and logwood appliances with a
detailed chemical characterization of both gaseous and
particulate phases.
Experiments have been carried out under
different output conditions (nominal and reduced) using
three modern pellet boilers and stoves and one modern
logwood boiler and stove. In addition, two types of
pellets (soft and hard wood) have been tested. After
dilution (20-40 times), biomass burning emissions were
aged through a potential aerosol mass-oxidation flow
reactor (PAM-OFR) (Kang et al., 2007) at ambient
temperature and environmentally relevant relative
humidity (40-70%). Both daytime (with OH radical) and
night-time (with NO3 radical, only for the logwood
stove) chemistry have been investigated. Furthermore,
“pure” secondary particles, formed by filtering (HEPA
filter) the entering emissions into the PAM-OFR, were
also studied. Primary and secondary emissions were
monitored using a high resolution-time of flight-aerosol
mass spectrometer (HR-ToF-AMS), a scanning mobility
particle sizer (SMPS), a condensation particle counter
(CPC), a multi wavelength aethalometer, a TEOM-50
(non-volatile PM fraction), a proton transfer reaction
time-of-flight mass spectrometer (PTR-ToF-MS) and gas
analyzers (CO2, O2, CO, NOx, total VOCs) providing
information on the particulate and gaseous chemical
composition, particulate size distribution and number
concentration. Moreover, effective particle density at
different aerosol size ranges have been investigated by
combining a differential mobility analyzer (DMA) and a
centrifugal particle mass analyzer (CPMA). Finally,
samples (filters and adsorbents) have been manually
collected at the emission and after dilution for
gravimetry and offline chemical analysis purposes.
Primary (notably PM and BC) and secondary
emissions measured will be compared and discussed in
terms of wood appliances, output conditions and fuel
used. Insights on the chemical composition of both
gaseous and particulate phases will be presented.
This work was supported by ADEME (Agency for
ecological transition) under grant 206C0004 and the
French Ministry of Environment.