At the 15 targeted nephelometer locations, plus an additional 14 locations near the burns, trained local personnel placed passive samplers to measure particulate matter and naphthalene for 24 to 120 hours and then sent the samplers to our laboratory for analysis. Due to winds shifting from the predicted direction, our samplers were directly downwind only at the Dunham burn. At that burn, although passive samplers were mounted on several telephone poles immediately adjacent to the burned field, only one PM10 nephelometer was successfully deployed. Highly elevated PM10 values were observed at the Dunham downwind monitor: a maximum hourly concentration of 6,500 µg per cubic meter occurred from 1:00 to 2:00 p.m., then a dramatic decline to 4.3 µg per cubic meter by 4:00 p.m. The average 24-hour PM10 concentration at this Dunham location was 276 µg per cubic meter, well above the federal criteria for unhealthy air, 150 µg per cubic meter . Although we only successfully deployed one monitor, the highly elevated concentrations were consistent with PM10 levels reported in another study of a burned field . Photo evidence was also consistent with visibility of less than 1 mile, which is expected at hazardous air levels . As noted, wind speed at this burn was somewhat higher than at the other burns . At several of the other 12 nephelometer locations, much smaller peaks were apparent in PM2.5 and PM10 after the burns were initiated, up to 57 µg per cubic meter of PM10 within the hour. Similar to the E-BAM findings, evening-to-morning peaks in PM2.5 and PM10 were observed. Although all of these peaks were relatively brief , these measurements were collected at places of public access, and even short-term exposures may have health risks. An increase in PM2.5 concentrations in air samples from city centers as low as 10 µg per cubic meter for as little as 2 hours has been associated with increased daily mortality in the surrounding population .At the laboratory, computer-controlled scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to obtain the individual sizes and chemistry of particles collected on the samplers. Then, PM2.5 and PM10–2.5 concentrations and particle size distributions were calculated using assumed particle density and shape factors and a particle deposition velocity model . In samples from the downwind locations at the Dunham burn,macetas plásticas por mayor concentrations of both PM2.5 and PM10–2.5 were elevated compared to an upwind sample. The fine fraction was primarily carbonaceous with a peak at the sub-micron range , while the coarse fraction had a lower carbonaceous percentage .
These carbonaceous percentages were higher than those measured upwind for fine and coarse fractions, as well as those reported for fine and coarse fractions in San Joaquin Valley ambient air . The coarse fraction in the downwind sample also had higher percentages of potassium, phosphorus and chlorine . Potassium and chlorine are considered potential indicators of biomass smoke , and phosphorus is found in most plant material. We also analyzed samples of unburned and burned bermudagrass and found that among inorganic elements, they contained similar peaks of potassium, phosphorus and chlorine . Their identification here may assist air pollution researchers attempting to identify sources of particulate matter in air samples. Naphthalene. Samples were analyzed for vapor-phase naphthalene by gas chromatography/mass spectroscopy.Naphthalene was occasionally detected at the five targeted burns with levels above the reportable limit at seven of the 23 locations near the burns and at one of the six more-distant locations . The highest level was detected in a sampler placed directly downwind of the Dunham burn. That highest level was lower than a reference level for respiratory effects , but only two samples were collected directly downwind and concentrations elsewhere in the plume could have been higher or lower. To compare, vapor-phase naphthalene measured in a laboratory from directly above the burning of agricultural debris was 60 µg per cubic meter . To assess health educational needs, we interviewed community leaders, community residents, farmers and school representatives from the agricultural area of Imperial County. We used a qualitative method called Key Informant Interviews , which allows for candid and in depth responses and the characterization of how interviewees discover and act on information. Potential participants were informed that the interview would take 30 to 60 minutes and that responses would be anonymous. If a respondent declined an interview, no information was recorded. Community leaders. Ten community leaders were interviewed out of 15 contacted. Those interviewed held management positions within either county environmental health agencies, nonprofit agencies that supported agriculture, or environmental organizations that promoted clean air. More than half of the community leaders ranked burning as a medium or high concern for their organization. Respondents representing the agricultural industry considered outreach important because, as one respondent said, “The public’s view of burning is fairly negative.” Suggestions for educational outreach included training for staff on the health impacts of smoke and “simple recommendations, options of actions to take during a burn.” Residents.
Seven interviews were conducted after we contacted 15 residents who lived either in single-family homes or apartments within 2 miles of fields. Most considered burning a high or medium health concern compared to other community health concerns. One person said, “You’re closing doors and windows, just trying to keep the smoke out.” No respondent had ever called or inquired with government agencies. One respondent explained, “We all have to live with our neighbors. . . it would be difficult to file a complaint or inquiry.” None of the respondents were aware of any educational materials. Farmers. Of 30 farmers that we contacted, three agreed to participate. All three burned bermudagrass or wheat fields, thousands of acres in some years. The farmers discussed the benefits: as one explained, “Burned fields are more profitable.” All had considered disking their fields or using minimum tillage as an alternative to burning, which they had learned about by trial and error. All three discussed a certificate program used by the Air Pollution Control District to accredit and stimulate financial rewards for farmers who do not burn . All three also had voluntarily notified their neighbors about planned field burns. .School representatives. Out of 30 contacted, we interviewed five teachers or superintendents who each worked at a separate school or district near historically burned fields. School representatives were concerned about enforcement. Their suggestions included: “Have people call a number if they notice illegal burning or something suspect” and implement “stiff penalties for those who don’t [follow burning rules].” They had ideas about community education, such as public service announcements on television. Two respondents, who were not enthusiastic about doing outreach, said, “There’s so much that we have to do.” This consideration may have also been part of the reason why the participation rate was low for key informants in this group, and possibly the farmer group.Responses from our key informants indicated that educational messages were needed. We developed two-page fact sheets for three Imperial County audiences — the general public, school representatives and farmers. These covered the reasons for burning, burn regulations, potential health impacts and behavioral recommendations to reduce exposures. In our studies,cultivo del arandano azul elevated particulate matter levels and visible drift were observed as far as 500 feet from the edge of burning fields, and wind directions could quickly change. We advised that anyone who could see or smell smoke or was within 300 feet of a burning field should go inside. If people had to be outside near a burning field, we recommended face-piece particulate respirators , which are available at most hardware stores. A worker who must be outdoors and near a burn must be in a respiratory protection program that includes medical evaluations and fit-testing of the respirator’s seal on the worker’s face . A draft of the fact sheet for the general public was tested with community members at a health clinic and shopping center. Although there were complaints about its length, the fact sheet was highly rated for usefulness: all 20 participants gave it either a four or a five on a scale of one to five . The final fact sheets were distributed to local organizations and are available on the Internet .In our studies, agricultural burning created potentially hazardous air levels immediately downwind; during evening-to-morning hours, PM2.5 levels increased 2 to 8 µg per cubic meter.
Many studies have associated total daily human mortality with mean daily particulate matter levels measured in urban centers, and some have observed a relationship at levels as low as 2 µg per cubic meter . In California, increases in children’s total daily hospital admissions for respiratory problems are also associated with increases in daily PM2.5 and potassium air levels, the latter an indicator of biomass smoke . To protect public health and potentially reduce exposures to smoke from agricultural burns, we recommend additional health education, smoke management and air quality research. Health education. Fact sheets are needed for other California counties where agricultural burning takes place, as well as educational materials for outdoor and field workers about respiratory mask protection and smoke visibility guidelines . As interviewees suggested, broader community education could include public service announcements. Smoke management. Currently, CARB declares a permissive-burn day when meteorological conditions ensure the regional dispersion of smoke, for example, a wind speed at 3,000 feet of at least 5 miles per hour . Imperial County’s smoke management plan states that the Air Pollution Control District may put in place additional restrictions based on meteorological and air quality conditions, including strong ground-level or gusty winds . We observed substantial drift at a slightly greater wind speed than that previously suggested for a vertical column of smoke to occur . Local Air Pollution Control Districts could reduce ground level drift by specifying a ground-level wind speed above which burns should not take place. Additionally, evening to-morning levels of particulate matter could be reduced if warranted by other restrictions, such as shortening allowable burn hours. Interviewed residents expressed reluctance to report neighbors who might be out of compliance. Supplemental Imperial County Air Pollution Control District activities could include online instructions about how to make a complaint. In addition, posting visibility guidelines for hazardous drift and a daily listing of the areas in the county where burns were scheduled would improve community notification. Research. Additional air monitoring is needed to further characterize the nature and extent of ground-level plumes and how they are affected by local crop type and conditions. Although crop-specific particulate emission factors from burning bermudagrass stubble have not yet been developed, factors for other grasses, such as Kentucky bluegrass, are about twice those for rice and wheat . The moisture level of burned residue can also significantly affect particulate matter emissions, with a change in moisture from 10% to 25% more than tripling particulate emissions during the burning of rice, wheat and barley straw . Ambient monitoring should also include indoor air, as outdoor PM2.5 may substantially infiltrate buildings , and we observed that outdoor particulate matter increases overnight when people are likely to be inside. Residents may be amenable to researchers installing unobtrusive passive samplers to monitor indoor air. In further studies, methods might be modified to allow the further identification of carbonaceous material, the gaseous component of other PAHs and some of the thousands of other volatile gases found in smoke . Information is also needed on whether residents are following recommendations to reduce their exposure to smoke from agricultural burning. Finally, farmers expressed a willingness to try alternative farming practices, notably tilling. We recommend further study of alternative farming techniques such as conservation tillage, which may reduce the need for burning, conserve water and soil, and reduce air quality impacts . In addition, integrating livestock grazing with grain and hay farming as a substitute for burning or tilling may reduce pests, herbicide use and erosion and provide additional income . Further study is needed on how farmers could viably integrate alternative techniques into current practices, particularly for local crops such as bermudagrass, and the estimated human health impacts of such changes.
