Environmental Engineering Reference
In-Depth Information
occupied major living areas with a wood-burning stove. Such practices were
anticipated to decrease overall space heating costs by reducing energy used
and substituting what was perceived to be a lower-cost and environmentally
friendly fuel.
As wood burning for space heating became popular, concerns were
raised about the potential impact of wood-burning appliances on ambient
air quality in communities where wood burning was common (e.g., Corval-
lis, OR; Butte, MT; Aspen, CO; and Watertown, NY). The impact of wood-
burning stoves on ambient air quality was deemed so great that the USEPA
promulgated a New Source Performance Standard (NSPS) for new wood-
burning stoves that manufacturers must meet to reduce emissions and pro-
tect ambient air quality.
Wood-burning stoves vary in design. There are two basic types: conven-
tional and airtight. Conventional stoves have relatively low combustion
efficiencies (in the range of 25 to 50%) and tend to cause significantly more
indoor and outdoor contamination that airtight stoves, which have combus-
tion efficiencies >50%. Efficiencies of new stoves covered by the NSPS have,
by necessity, increased in order to meet regulatory requirements. Wood
stoves and furnaces that comply with the NSPS have significantly lower
emissions of CO and particles to the atmosphere.
A variety of investigators have attempted to determine the impact of
wood-burning appliances on indoor air quality (IAQ). Special attention has
been given to contaminants such as CO, NO, NO
, SO
, RSP, and PAHs.
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Elevated indoor levels of NO, NO
have been reported in some
studies but not others. Reports of elevated indoor CO and RSP levels asso-
ciated with wood appliance operation have been more consistent. Carbon
monoxide concentrations in houses with nonairtight stoves have been
reported in the range of a few parts per million (ppmv) to 30 ppmv (the
latter under worst-case operating conditions).
Wood-burning appliances produce smoke, which is a combination of
particulate and gas-phase contaminants. The former gives wood-burning
smoke its “visible” characteristics. Smoke tends to leak from nonairtight
stoves during operation and from both airtight and nonairtight stoves during
refueling.
The effect of wood-burning appliance operation on indoor RSP concen-
trations has been evaluated by investigators who have made measurements
of RSP in both indoor and ambient environments and compared them by
calculating indoor/outdoor ratios. Significantly higher indoor/outdoor
(I/O) concentrations were always observed for residences during wood-
burning appliance operations. Highest I/O ratios were reported for non-
airtight stoves (4 to 7.5:1) and fireplaces (6.1 to 8.5:1); lowest ratios were in
homes with airtight stoves (1.2 to 1.3:1). It must be noted that these ratios
were likely biased (to lower values) by higher outdoor suspended particle
concentrations due to the operation of wood-burning appliances themselves.
The particulate phase of wood-burning emissions includes a variety of
substances, most notably PAHs, a group of compounds with considerable
, and SO
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