Report by The Davis Wood Smoke Scientific Advisory Committee
The immediately preceding Part 1 of this 2-part series on wood burning in Davis reported how voluntary wood burning restrictions in Davis have proved ineffective in solving the increasing problem of wood smoke in the city (click to see “Why Voluntary Wood Burning Restrictions are Not Working in Davis“) This 2nd article in the series reports the results of the Davis Wood Smoke Scientific Advisory Committee and how they confirm the adverse health impacts that wood burning may have on downwind neighbors. It confirms the appropriateness of restricting wood burning based on projected local weather conditions as previously recommended by the Davis Natural Resources Commission instead of projected regional particulate matter concentrations as currently practiced by the local air quality management district
The issue of wood burning restrictions has been raging in Davis for over 5 years. On one hand you have environmental scientists, including myself, and members of the health community generally arguing for more severe restrictions on wood-burning to reduce citizen exposure to wood smoke. These proponents of greater wood burning restrictions argue they are necessary in order to protect public health – particularly for susceptible individuals such as children, seniors, and those with respiratory impairments. This group generally claims that wood smoke is extremely toxic and has high carcinogenic potential. Further, it is claimed that wood smoke is often produced in such prodigious quantities from stationary sources that regulation of wood burning could produce significant public health benefits for the population at large.
On the other hand, others claim the whole problem is overblown. Some, such as Dr. Tom Cahill of UC Davis claim that wood smoke is not as harmful as previously suspected and that there is actually very little wood smoke in our air – or certainly not enough to have a major adverse effect on public health. Other pundits like Bob Dunning of the Davis Enterprise and some readers of this publication claim that regulation of wood smoke represents an unnecessary intrusion of the government into the private lives of citizens in Davis.
Over the past years, the Davis Natural Resources Commission (NRC) and the Davis City Council have been faced with choosing between these competing claims. While the NRC has typically chosen to err on the side of public health and has advanced a series of proposals to the Davis City Council, past Davis City Councils has noted the uncertainty in the magnitude of the problem as indicated by opponents and proponents of wood burning. Combined with their obvious political considerations, they have rejected these previous proposals by the NRC.
In almost all other populated areas of Northern California, the arguments promoting increased regulation of wood smoke through mandatory restrictions have carried the day; albeit under the force of law and threats by the US Environmental Protection Agency. Indeed, the majority of wood burning regulations have been enacted because the jurisdiction in question was forced to implement the restrictions in order to meet federal air quality standards. That is, when it was projected that regional air quality was projected to exceed allowable federal standards with respect to particulate matter, the regional air quality management district in that area would call for a mandatory, but temporary, 24-hour cessation of wood burning. This would allow for the regional particulate air concentration to drop below federal standards during the following day in question. Failure to implement these types of mandatory restrictions by an air quality management district could have resulted in the loss of federal highway transportation subsidies worth tens to hundreds of millions of dollars to that region.
However, unlike 95% of the population of Northern California from Bakersfield to Sacramento and including the entire 9-county Bay Area, Davis happens to be in the Yolo Solano Air Quality Management District – YSAQMD. The YSAQMD has not yet been forced to implement these restrictive prohibitions against wood burning when regional air quality is projected to exceed federal standards. This may change within a number of years as the YSAQMD was also declared in 2009 to be in “non-attainment” with respect to federal particulate air quality standards. However, the YSAQMD has appealed that decision and it is uncertain if it will be forced to implement similar wood burning restrictions if the non-attainment designation is not eventually upheld.
However, the NRC proposals submitted to the City Council in the past have gone beyond restricting wood burning only when regional air quality standards are in danger of being exceeded. This is because use of wood burning appliances under certain atmospheric conditions can result in very high localized wood smoke concentrations that significantly exceed particulate air quality standards and adversely affect nearby residents. The NRC proposed that the operation of wood burning appliances therefore needs to be regulated so as not to cause significant health risks to residents who live downwind near the local sources of wood smoke.
This alternate approach was taken because it became clear from local studies that there were instances when some citizens were being exposed to concentrations of wood smoke that far exceeded federal standards even though regional ambient wood smoke concentrations were not in excess of federal standards. That is, pockets of wood smoke could accumulate in neighborhoods or around individual homes when wood smoke concentrations are not a regional concern. Because it was determined that these pockets or localized accumulations of wood smoke formed in very close proximity to the location where the wood smoke was produced, this became known as “nearest neighbor” impacts of wood smoke although that is not a generally recognized term used in the wood burning community.
That excessively high concentrations of localized wood smoke can occur in Davis was proven during the 2009 – 2010 wood burning season when dozens of citizens registered complaints of excessive exposure to wood smoke. Further, the California Air Resources Control Board (CARB) installed a local air quality monitor at Slide Hill Park in East Davis that winter. The results from the study showed that the air measured at that site had particulate matter, on average, greater than any other of the several dozen CARB monitoring stations in the entire region (click to see “Hold Your Breath in East Davis During the Winter“, Davis Vanguard, June 3, 2010″).
Indeed, the measurement showed that at that site the particulate matter concentrations were so great that the air was deemed to be “Unhealthy for Sensitive Individuals” on 19 days that winter compared to 1-2 days for other sites monitored in Davis. The highest concentrations otherwise measured anywhere in the entire Sacramento region only showed 12 such days in which the air was determined to be “Unhealthy for Sensitive Individuals”.
To determine the extent of how much smoke may accumulate in these localized environments, EPA-approved computer modeling tools were used to identify those conditions under which these unhealthy accumulations of wood smoke could occur. These modeling tools weighed the impacts of wind speed, atmospheric turbidity, and air temperatures, and the amount and physical characteristics of the smoke discharged from chimneys by different types of wood burning appliances including open hearth fireplaces, EPA-approved wood stoves, and the most modern and efficient wood and pellet stoves.
Proponents of more strict wood burning restrictions point to this and similar studies showing excessively high wood smoke concentrations as justification for using more advanced modeling tools to predict safe conditions under which wood burning could occur rather than using the overly simplistic regional air quality methodology otherwise used by the YSAQMD when calling Don’t Light Tonight voluntary alerts. Proponents of more wood burning restrictions also claim that the exorbitantly high concentrations measured also represent a very real and immediate public health issue justifying the need for restrictions to be mandatory instead of voluntary as currently exist in the YSAQMD’s jurisdiction.
Opponents of the NRC-proposed wood burning restrictions (including Mat Ehrhardt of the YSAQMD and Jacques DeBra of the Davis Public Utilities Department) otherwise claim that the modeling tools used by the NRC in establishing safe and unsafe wood burning conditions were unproven and not verified by actual experimental data. They further claim that the primary sources of wood smoke in Davis are derived from regional rather than local sources and thus local controls of wood burning would be generally ineffective in protecting Davis residents from excessive wood smoke exposures
To ascertain the validity of the competing claims regarding the toxicity of wood smoke, the sources of excessive wood smoke measured in Davis, and the ability of computer modeling to accurately predict the conditions under which localized wood smoke concentrations can be excessive, the Davis City Council requested that the NRC consult an independent body to obtain non-biased information.
To accommodate this request, the Wood Smoke Subcommittee of the NRC then requested a group of world-recognized experts in atmospheric science and respiratory toxicology to convene and evaluate the currently available scientific information. They were further requested to provide guidance about the toxicity of wood smoke, to evaluate competing technical claims regarding the sources of wood smoke, and to determine the usefulness and accuracy of computer models in predicting localized wood smoke concentrations.
The Davis Wood Smoke Scientific Advisory Committee Report was thus formed and comprised of 4 individuals from UCD that each had exceptional credentials in their field. The Committee was provided with the NRC-Recommended Wood Smoke Ordinance and asked to consider these recommendations when providing their analyses and opinions. The full report is fairly short and easily read by clicking on the following link – Davis Wood Smoke Scientific Advisory Report.
The four members of the Davis Wood Smoke Scientific Advisory Committee included two atmospheric scientists and two respiratory toxicologists. All are world-renowned and represent the highest levels of technical expertise in their fields.
1. Dr. Tony Wexler
- Director of Crocker Nuclear Laboratory, University of California, Davis
- Director, Air Quality Research Center, University of California, Davis
- Director, San Joaquin Valley Aerosol Health Effects Task Force, University of California, Davis
- Professor – Department of Mechanical and Aerospace Engineering, University of California, Davis
- Professor – Department of Civil and Environmental Engineering, University of California, Davis
- Professor – Department of Land, Air and Water Resources University of California, Davis
2. Dr. Lowell Ashbaugh
- Associate Research Ecologist – Crocker Nuclear Laboratory, University of California, Davis
- PM Review Panel, Clean Air Scientific Advisory Committee, U.S. Environmental Protection Agency, 2008 – present.
3. Dr. Kent Pinkerton
- Professor – Department of Pediatrics, School of Medicine, University of California, Davis
- Professor (In-Residence) – Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis
- Director – Center for Health & the Environment, John Muir Institute of the Environment, University of California, Davis
- PM Review Panel, Clean Air Scientific Advisory Committee, U.S. Environmental Protection Agency, 2008 – present.
4. Dr. Laura Van Winkle
- Associate Adjunct Professor – School of Veterinary Medicine Department of Anatomy, Physiology and Cell Biology, University of California, Davis
- Associate Research Cell Biologist – Center for Health and the Environment, John Muir Institute of the Environment
Following are some excerpts from the report issued by these esteemed scientists along with the specific respondents to the noted subject matter:
Toxicity of Wood Smoke (Respondents: Drs. Laura Van Winkle and Kent Pinkerton)
- “Wood smoke contains low levels of compounds that are either carcinogenic and/or possibly carcinogenic. The dose dictates the level of concern and this is the product of both the duration of exposure and the length of time of exposure.
- “Exposure to high levels of wood smoke in healthy adults results in increased oxidative stress in the lung and airway mucosal symptoms. Wood smoke has been shown to aggravate asthma and is associated with increased risk of coronary events. At a minimum, wood smoke can trigger an abrupt change in breathing pattern, especially in susceptible individuals.”
- “A likely significant adverse effect from wood smoke exposure in Davis is exacerbation of pre-existing respiratory and/or cardiovascular conditions in susceptible populations. Asthma exacerbations have been linked to exposure to PM2.5 from combustion of wood. The level of smoke the person is exposed to, the local concentration, is a determinant of severity of effect.”
- …”reduced wood smoke concentrations would improve respiratory and cardiovascular health in susceptible populations”
Re: Sources of Local Wood Smoke in Neighborhoods (Respondent: Dr. Anthony Wexler)
- “Local wood burning, such as in fireplaces and wood stoves, when the air is stagnant or moving very slowly can produce very high concentrations near the source since minimal air movement does little to dilute the emissions. Also, regional wood burning will affect a larger portion of Davis, while local wood burning under stagnant air conditions will most affect those close to the source.”
Usefulness of Modeling Dispersion of Wood Smoke Emissions from Chimneys and Estimating Ground-Level Concentrations of Wood Smoke (Respondent: Dr. Anthony Wexler)
- “Plume dispersion modeling is a standard technique that has been used and perfected over many decades to predict the concentrations of pollutants downwind from stacks. These methods are state-of-the-art and usually produce quite accurate predictions.”
- “Screen3 is a plume dispersion model used exactly for the purpose of predicting where plumes go when emitted from stacks and chimneys. It is a standard tool used by government, industry and environmental groups.”
Re: Estimating Wood Smoke Exposures (Respondent: Anthony Wexler)
- “…the federal standards do not address exposures that may be very high compared to the standard but for a shorter period of time than the standard addresses. The EPA sets air quality standards that protect human health but they have to have evidence to establish standards. It is very difficult to obtain human health data for such high, short term exposures, so standards for these have not yet been set. In the absence of more data, the calculation that you have done is reasonable for protecting the health of Davis residents.”
Re: Effectiveness of Different Control Strategies (Respondent: Dr. Lowell Ashbaugh)
- “Air quality regulations are set to provide protection from the adverse effects of air pollutants “with a sufficient margin of safety” to protect the general population. Wood burning restrictions based on not exceeding the regional air quality standards would probably not protect people living close to the burning. Regional air quality monitors are sited to obtain data that is regionally representative, while wood burning impacts are more likely to be close to the wood burning source. This is especially true for sensitive populations, who could experience smoke concentrations far in excess of the health-related standard simply due to their proximity to the source. Such “hot spots” of smoke pollution could exist with no appreciable impact on the measured regional air quality. The approach you have devised to define a meteorological matrix is well thought out and constructed. It acknowledges that the atmosphere has a capacity to dilute wood smoke that varies with regional air pollution and ventilation (wind speed). When air quality and dilution conditions allow it, more polluting activities (open fireplaces) can be used. As conditions become more restrictive, the allowable wood burning devices shift to those that are more efficient. Under extreme conditions, wood burning is not allowed. This approach is certainly reasonable and protects both those sensitive to the pollution and those who have invested in cleaner burning technology.”
Re: Adequacy of Data and Future Research Needs (Respondent: Dr. Lowell Ashbaugh)
- “While scientists would always like more data, at some point there is enough accumulated evidence that protective actions are justified. In this case the scientific evidence for the existence of health-related impacts of wood smoke is more than adequate to justify an ordinance to protect people living nearby. Federal fine particle standards are periodically reviewed to accommodate more information as it becomes available. The standards are set now to protect the population based on current knowledge of health effects. Susceptible populations living near sources of pollution, whether wood burning or other sources, can be exposed to much higher concentrations than the standards allow”.
- “A useful analogy to consider here is Davis’ smoking ordinance. Smoking is not allowed in public buildings or within 20 feet of their entrances. This form of pollution has no effect on regional air quality but certainly affects people who happen to be nearby. A significant difference between smoking and residential wood burning is that wood burning can affect people in their homes and yards where they cannot escape, while we can usually move away from smokers to protect ourselves.”
The opinions of these scientists overwhelmingly conclude that wood smoke is a serious health hazard (particularly to susceptible groups – children, the elderly, and people with impaired respiratory systems). Indeed, they claim that high localized wood smoke can actually trigger asthma attacks and respiratory distress.
They also conclude that existing standards and wood burning restrictions programs promulgated by various AQMDs do not provide protection against the very high concentrations of wood smoke that can occur immediately downwind from wood burners. They further claim that the methodology used to predict these concentrations in the previous NRC-recommended ordinance is appropriate and probably very accurate. The committee further unequivocally states that the approach taken by the NRC to control these exposures is reasonable and provides protection to sensitive groups while allowing more frequent wood burning from those who have invested in truly cleaner burning technology.
The Committee’s report should conclusively settle the debate about the adequacy of the science behind the NRC’s recommended approach toward regulating wood smoke and about the high toxicity of wood smoke. With this justification, there is really no longer any excuse for the Davis City Council to continue to hide behind the skirts of uncertainty and ambiguity and they should move aggressively toward enacting a truly protective wood smoke ordinance.
At the moment, I am speaking as a member of the medical community, and as such am strongly in favor of limiting wood burning to reduce health risks to susceptible individuals.
I do feel that there is a legitimate opposing concern from those whose sole means of heating their homes is wood burning. I do not know how many Davis homes this might apply to, but I do know that until last year that was the sole source of heat in a Village Homes house owned by a friend and was also the sole source in the old east Davis home that I just bought.
I am unaware if their are allowances or mitigations for these individuals under consideration. Alan or others, do you know ?
To: medwoman re “sole source of heat”
The previous NRC recommendations all included provisions excepting homes if wood was their sole source of heat – either because they had no other heat source, their heating equipment was temporarily broken, or there were power outages.
To alanpryor: From your first article, you seem amenable to putting this “issue” to a public vote. So my next question is twofold:
1) What is your/NRC’s specific proposal (precise language) for a wood-burning ordinance?
2) What enforcement mechanism to you propose be put in place to ensure such an ordinance is enforced?
As to medwoman’s comment, when stating the specific proposal, also include any/all exemptions/exceptions and the like…
So let’s see if I’ve got this right, if fireplace smoke is truly hazardous to others it will be okay to still harm others health if the fireplace is the only source of heat in one’s home?
Here is the recommended ordinance I saved from 2010:
[url]http://davismerchants.org/vanguard/NRCWoodBurningOrdinanceRecommendation.pdf[/url]
@ rusty: Yes.
So Don, doesn’t that kind of defeat the point?
Rusty: in answer to your question, I think there are two central issues one is proximity and the other is quantity. So to answer your question, if you are next to someone using the fireplace, it doesn’t matter. However, if you have a handful of people burning rather than hundreds or thousands, then the cumulative effect is less harm. But personally I think in this case the income issue is a non-issue. If you are low income you probably qualify for a subsidy from PGE and that’s where I think we need to focus any aid, not granting waivers for burning wood.
I think we as a population should stop paying attention and giving any credibility to a minority of people who would ban this or that because they simply don’t like it and want to dictate to everyone else how they have to behave. It’s time to nip this NRC in the bud before they really get out of hand.
Rusty, I think you are going to be disappointed, as time goes on and the impact of global warming gets worse and becomes more apparent, I think you are going to see more and more restrictions. We are not going to be able to burn stuff for fuel in the near future if we want our species to be able to survive.
When I choose to burn wood in my stove over burning natural gas in my furnace (or natural gas at a power plant that feeds my electric heat pump), I’m effectively choosing a lower carbon footprint form of heat. My wood comes from the farmers walnut and almond orchard down the street. Those trees in the past were pulling carbon dioxide from the atmosphere to build the cellulose that I’m burning to heat my house in the present. On top of that, I’m providing my neighbor a secondary line of income. This all makes me feel good. Please don’t make this about global warming.
You are not accounting for economies of scale when you are arguing you are using a lower carbon footprint. But actually I was not suggesting this was a global warming issue specifically, rather I was responding to Rustys ban this argument by suggesting we will see more activities curtailed or banned in the global warming era.
Good grief David, economies of scale?! You do know that the best argument this proposed ordinance has is neighbor to neighbor nuisance. The scale is at the individual level. Don’t make this about global warming.
To Don Shor: Thanks for the link. I wonder if enforcement of such an ordinance is going to run into the same types of problems enforcement of the noise ordinance has run into…