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A Cloud of Wood Smoke Forms Every Winter



Wood Smoke from Residences is the Primary Source of Particulate Pollution during Winter Months

Most wood-burning occurs during the late fall through winter seasons and usually during evening hours. Oftentimes in the winter, stagnant air conditions occur with very little to no wind. Temperature inversions occur under these conditions in which a blanket of air traps smoke and other pollutants near the ground. These conditions result in the rapid build-up of outdoor smoke affecting not only people at the source of the smoke but also neighbors within the source’s vicinity. Even on windy days, smoke from a chimney can result in excessive smoke exposure to downwind neighbors.

Wood-burning is the primary contributor to particulate pollution during winter months. During this period, wood-burning produces quantities of PM10 and PM2.5 particulate matter (particles less than 10 micrometers in size or less than 2.5 micrometers in size, respectively) that are far in excess of those produced by agriculture or industry combined.

”Almost half of our particulate matter pollution comes from wood burning fireplaces. For folks with asthma, this can be life-threatening” (Quote from Reference 2 referring to the Sacramento, CA area)



Wood Smoke Affects Non Wood-Burning Residents Even in the Privacy of Their Own Homes!

When stagnant air conditions occur, use of a single wood-burning fireplace or insert can cause a buildup of particulate pollution in a neighborhood’s air which is far in excess of the allowable federal 24-hour PM10 standard of 150 micrograms/cubic meter and the 24-hour PM2.5 standard of 35 micrograms/cubic meter (see below). “Even if you don’t burn wood, studies have shown that wood smoke from neighbors’ fires can enter your home. Smoke particles are so small they can seep into a home with closed windows and doors. The pollution levels inside a closed home can be up to 70 percent of the levels outdoors” (Quote from Reference 1).

Thus, while you or members of your family may not suffer tremendously from exposure to wood smoke, there almost certainly are some individuals in your neighborhood to which exposure to high concentrations of wood smoke can cause serious medical consequences. Indeed, pollution from a single fireplace if not almost immediately dispersed is sufficient to induce asthma attacks, migraine headaches, cardiac irregularities, and full respiratory failures leading to hospitalization in some individuals.



Most People Do Not Realize How Much Pollution is Produced by Use of Wood-Burning Appliances

Fireplaces and wood-burning appliances produce particulate pollution far in excess of most other sources commonly considered to be very polluting. Following are the hourly and PM10 emissions produced from different sources:

Particulate Emissions
Pollution Source (grams/hour) (grams/day)

Open Heath Fireplace 59 1,416
(Upper Range of Emissions)

Open Heath Fireplace 30 720
(Lower Range of Emissions)

One New 300 HP Diesel Truck 18 432
(Running Full Throttle)

One Non-EPA-Certified Fireplace Insert 15.6 374.4

One EPA-Certified Fireplace Insert 8.2 196.8

One Cigarette Smoker (0.04g/cigarette) 0.48 0.8
(One Chain-smoker (One Avg. Smoker
at12Cigarettes/Hour) at 1 pack/day)
(Data from Reference 1 below)








On a comparative daily basis, one open hearth fireplace at the upper range of emissions produces particulate pollution equivalent to about 1,770 average smokers or over three 300-HP diesel trucks running at full throttle. Few fireplace users would appreciate it if equivalent amounts of pollution from either of these sources were wafting over into their bedroom windows from their neighbors’ backyards.

By contrast, natural gas or propane-burning space heaters produce far less particulate pollution. “The inhalable particle pollution from one woodstove is equivalent to the particle pollution emitted from 3,000 gas furnaces each producing the same amount of heat” (Quote from Reference 4 below).

Since almost all of the PM10 particulate matter in smoke pollution is actually less than 2.5 micrometers (microns) in size (see Reference 1), the above emission rates are also very good proxy values for the amount of PM2.5 pollution in wood smoke.



Wood Smoke Mostly Affects Those Closest to the Source

As deleterious as wood smoke is on regional air quality, the effects are much more serious when wood smoke accumulates under stagnant conditions in the neighborhood or general vicinity of the wood smoke source. When stagnant air conditions occur with very little to no wind, a blanket of air traps smoke and other pollutants near the ground. These conditions result in the rapid build-up of outdoor smoke that can affect all neighbors within the source's immediate vicinity. Depending on the type of fireplace or insert used and the burning duration, smoke can concentrate under such conditions to many times the allowable Federal 24-hour Particulate Standards within a matter of hours.

For instance, with completely still air, a single open hearth fireplace emitting 59 grams/hour of PM particulate pollution into the air surrounding a normal city block (16 houses) will cause the concentration of PM particulate matter in the 100 ft. high environmental envelope above that block to rise to over 4,500 micrograms per cubic meter. This is over 30 times the 24-hour Federal Standard for PM10 pollution of 150 micrograms per cubic meter and over 131 times the 24-hour Federal Standard for PM2.5 pollution of 35 micrograms per cubic meter.




And, as shown in the following table, even a comparatively "clean-burning" EPA Phase II - Certified wood stove or insert operating in completely stagnant air conditions will result in PM accumulations in a 1-block area rising to greater than the Federal 24-hour PM10 Standard in only about 5 1/2 hours. Similarly, under the same meteorological conditions the particulate emissions of such an EPA Phase II - Certified stove or insert would raise the neighborhood PM concentrations to greater than the Federal 24-hour PM2.5 Standard of 35 micrograms per cubic meter in just over 1 hour!

I

Of course, completely stagnant air conditions extending over a full 24-hour period or of a sufficient duration that can result in these extremely high concentrations are rare in most locales. However, conditions approaching completely stagnant air can frequently occur during atmospheric inversions in winter months such as often seen in California's Central Valley.

And even with slight winds, wood smoke emitted from a chimney of a wood-burning appliance under relatively stable weather conditions can result in excessive smoke exposure at ground level to downwind neighbors. This can occur as a plume of smoke begins to broaden and disperse at ground level after exiting a chimney. The location, size, and concentrations of pollutants in such a plume depends on the distance from the source and the prevailing atmospheric conditions at the time of release.

The dispersion pattern and steady-state ground level concentrations of the particulate pollution in such a plume can be calculated, however, and then plotted on maps as isolines and/or color gradients to represent the areas of different concentrations in the plume.

As an example, a single open hearth fireplace will produce an average of 44.5 g/hr of PM 10 and PM2.5 particulate pollution. Assuming stable atmospheric conditions with a mild wind of 1 meter/sec (about 2.25 mph), the plume size and concentrations that are expected to occur are represented by the multi-colored vertical stripes in the center of the following picture of a neighborhood school.




In this example, ground-level particulate pollution concentrations in excess of 73 micrograms per cubic meter were predicted to be produced about 250 feet downwind from the source - or directly over the school. The areas of lesser concentration immediately surrounding the plume "hot spot" are represented by lighter colors and were also mostly predicted to be in excess of or near the 24-hour PM2.5 standard of 35 micrometers per cubic meter. Of interest, the fireplace polluter is exposed to virtually NONE of their own PM pollution! As long as even a mild wind is blowing, they are exporting it all beyond their property lines to their neighbors which, in the above case, happens to be an elementary school.

One should also note that the plume of particulate pollution produced by such a wood-burning appliance is actually far broader than that shown in the above example because only the isolines of the highest concentrations are shown. The largest area of the plume (which represents the lowest range of concentrations from 0 - 18 micrograms per cubic meter) is not shown at all on the picture and actually extends well over the school's ground surface area compared to only the excessively higher concentrations in the center of the plume displayed in the above picture.

Also note that these plume concentrations assume that zero particulate matter is already in the atmosphere. If ambient conditions are such that background particulate matter concentrations approach or exceed the Federal 24-hour PM2.5 standard of 35 micrometers per cubic meter (as can often be the case during winter months when stagnant weather conditions exist and fire wood-burning is at its height), the actual area in which exposure to particulate matter pollution occurs in excess of the Federal Standard would be substantially larger than even that shown in the above picture.

Further, much wider plumes with even greater concentrations of ground-level particulate pollution can occur when numerous houses in the same neighborhood are burning wood simultaneously. The cumulative adverse effect that this has on downwind air quality can also be quantitatively predicted. As an example, the following picture identifies a neighborhood of 130 homes directly to the south of a large senior retirement community. Assume 10% of these homes at randomly-selected locations were simultaneously burning wood at the emission rates specified in the picture.




If the atmosphere were stable and the prevailing winds were mild and in the direction of the senior center, excessively high concentrations of particulate pollution would result in the air surrounding the senior center. As shown in the following picture, the highest ground-level concentrations of particulate matter pollution produced under these conditions are expected to reach over 120 micrograms per cubic meter - or over 3 times the 24-hour PM2.5 standard. A broad plume of particulate pollution also in excess of the Federal Standards extends outward from the highest concentration areas. Including the unseen low concentration portion of the plume, the senior facility is functionally awash in particulate pollution - none of which is their own making.






About the Dispersion Model

All of the concentrations and locations of the various dispersion plumes displayed in this document were calculated using software employing the US EPA Industrial Source Complex Dispersion Models (ISC3). In the interests of brevity, only the most relevant input parameters are provided that were used to calculate the isolines and concentrations shown in the examples. A more detailed description of the algorithms of the model is available in the User's Guide for the Industrial Source Complex (ISC3) Dispersion Model, Volume II - Description of Model Algorithms (EPA Publication 454/B-95-003b) which can be freely downloaded at www.epa.gov/scram001/userg/regmod/isc3v2.pdf.



References

1. Staff Report on San Joaquin Valley Air Pollution Control District Rule 4901 - Wood Burning Fireplaces-Stoves, June 19, 2003

2. Jeff Starsky, Chairman of the Sacramento Air Quality Management District, Insights, Capital Public Radio November 21, 2006

3. Sam Atwood, South Coast Air Quality Management District, “Pollution Linked to Premature Deaths”, KABC Channel 7, June 1, 2007

4. California Air Resources Board, Consumer Information Sheet, “Reducing Air Pollution from Residential Wood Burning”, September 12, 2005

5. Staff Report on Sacramento Air Quality Management District Rule 421 – Wood-Burning Appliances, September 27, 2007

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