The effects of ozonation on particulate matter were studied on a commercial broiler farm. The farm consisted of 4 identical tunnel-ventilated houses (12.8 × 152.4 m): 2 houses were treated with O3 (maximum concentration 0.1 ppm) and the other 2 served as control units. The particle size distributions of total suspended particulate (TSP) samples from both control and treated houses were found to have very similar profiles with no statistical difference. The TSP concentrations were significantly higher in treated houses as compared with those in control houses, and the mean of the differences was 5.50 mg/m3. In both treated and control houses, there were substantial vertical TSP concentration gradients and the concentrations decreased with height. At broiler chicken height (0.28 m), TSP concentrations were 13 ± 3 mg/m3 in control houses and 17 ± 2 mg/m3 in treated houses. At human breathing height (1.55 m), TSP concentrations were 8 ± 4 mg/m3 in control houses and 7 ± 2 mg/m3 in treated houses. Particle phase NH4+ concentrations were higher in treated houses (ranging from 0.59 to 42.01 mg/m3 with mean = 17.49 mg/m3) than in control houses (ranging from 0.34 to 13.55 mg/m3 with mean = 4.42 mg/m3). The TSP samples from locations in the vicinity of the farm showed higher concentrations downwind than that upwind, but there were no significant differences observed among different ambient locations for TSP NH4+ concentrations. The results from this study did not show that direct application of ozonation technique has beneficial effects for particulate matter control in broiler houses.
Particulate matter (PM) and gaseous emissions from animal feeding operations (AFO) are of increasing concern. Due to adverse health effects and the magnitude of emissions, NH3 and PM are considered major pollutants emitted from poultry houses (Ad Hoc Committee on Air Emissions from Animal Feeding Operations, 2003; Heederik et al., 2007; Mitloehner and Schenker, 2007; Centner and Patel, 2010). To comply with increasingly stringent state and federal air pollution regulatory requirements for air emissions, the mitigation of NH3 and PM has become an urgent need for the poultry industry.
In the past 2 decades, a significant amount of work has been done on developing strategies for controlling and mitigating air emissions from AFO. Generally speaking, these mitigating strategies can be classified into 3 basic categories. The first category is feed management, or dietary manipulation (e.g., feed composition, feed, and water additives). Feed management aims to reduce the nitrogen excretion in feces and urine by matching the amount and composition of feed more closely to animal requirements (Panetta et al., 2006; Powers et al., 2007). Also, dietary manipulation may induce a change of urine and slurry pH and moisture contents (Canh et al., 1998). The second category is waste management-treatments. The design of manure collection, removal, and storage system has been developed to reduce emissions (Lim et al., 2004; Melse et al., 2009). Changing the chemical-physical properties of the manure has also proved to be able to reduce emissions (Hartung and Phillips, 1994; McCrory and Hobbs, 2001). The third category is internal air cleaner-exhaust air treatment. Internal filtration, electric precipitation, and wet and centrifugal collections are commonly used internal air cleaners and has proved to reduce emissions (Tan and Zhang, 2004). Treatments of the ventilation air from AFO have been extensively studied. Methods of these exhaust air treatments include vegetative buffers, windbreak walls, biomass walls and biocurtains, biofilters, single pollutant-stage scrubbers, and multistage-multipollutant scrubbers (Ad Hoc Committee on Air Emissions from Animal Feeding Operations, 2003; Tan and Zhang, 2004; Melse et al., 2009).
Among various mitigation technologies for animal house air pollution control, room ozonation is a controversial technique that attempts to remove emissions from internal air. Reported results for NH3 mitigation by ozonation are somewhat contradictory (Keener et al., 1999; Yoloyama and Masten, 2000; Elenbaas-Thomas et al., 2005; Li et al., 2009; Wang et al., 2010;). Keener et al. (1999) reported that O3 treatment at a concentration level of 0.15 ppm removed 58% of NH3 and 60% of the dust mass in a swine building, whereas Elenbaas-Thomas et al. (2005) indicated that room ozonation in a swine building at a maximum O3 concentration of 0.1 ppm did not result in any statistically significant reduction in dust mass concentrations, odor concentrations, sulfur compound concentrations, or bacteria counts. Moreover, the study found that significantly higher NH3 concentrations were observed in the O3-treated room as compared with the room without O3 treatment. Li et al. (2009) recently conducted a series of laboratory experiments and discovered that O3 had no significant effect on NH3 emissions. Moreover, it was reported by Li et al. (2009) that with O3 treatment, a high concentration of particles in the high-risk respiratory fraction were generated.
As for PM mitigation, the EPA (2008) reported that O3 could not remove particles (e.g., dust and pollen) from the air. Moreover, O3 could react with preexisting particles. These interactions can affect the growth of these preexisting particles (Lee et al., 2004), change particle surface chemical characteristics and composition, and alter their toxicity (Pitts et al., 1985; Enya et al., 1997; Ishii et al., 2000). In AFO environments, tremendous amounts of NH3 and a variety of volatile organic and inorganic compounds are released from animal waste (O’Neill and Phillips, 1992; Schiffman et al., 2001). Some of these compounds are very reactive and can undergo chemical reactions with O3, leading to low-vapor-pressure products. These low-vapor-pressure products can form particles through homogeneous nucleation-nucleated condensation. Also, they can condense onto preexisting particles, and the preexisting particles can grow up to larger sizes (Grosjean, 1992; Lee and Kamens, 2005; Li et al., 2007).
Although study of the ozonation technique has been a topic for decades, there are still gaps in the knowledge concerning the application of this technique for mitigating air pollution in AFO. This research aims to examine the effect of ozonation on PM in a poultry housing environment to allow us to make inferences about causation between ozonation and PM.
MATERIALS AND METHODS
Broiler Houses and Room Ozonation Settings
This study was conducted on a commercial broiler farm in North Carolina. The layout of this farm, as shown in Figure 1, consisted of 4 identical tunnel-ventilated houses (12.8 × 152.4 m) with 21,500 broilers per house. Two identical O3 generators (AgriO3, Dahlonega, GA) were installed outside of houses 2 and 3. Ozone was generated continuously and introduced to these 2 houses through polyvinyl chloride pipes on the ceilings. Ozone concentrations in these 2 houses were controlled below 0.1 ppm and were monitored with GasAlert Extreme (BW Technologies, Arlington, TX) and spot-checked with colorimetric sampling tubes and O3 Hunter Plus (AET-030P, New Cosmos Electric Co. Ltd., Osaka, Japan); 0.1 ppm is the limit of any exposure time from the National Institute for Occupational Safety and Health (NIOSH, 2008). The other 2 houses (1 and 4) were designed to serve as control units. Except for the ozonation, all other operational parameters were managed in the same manner through the 4 houses (e.g., feed, number of chickens, and ventilation system settings).
PM Sampler Placements
Particulate matter sample collections were accomplished by conducting 3 sets of PM sampling events over 8 consecutive days when the chickens were 6 to 7 wk old in January 2008. The ventilation system in each house was set to winter mode. In this mode, only 2 minimum ventilation fans were operating for 2 min on and 5 min off alternately. The ambient temperature was in the range of −0.5 to 10°C during the sampling period.
For the first set of PM sample collections, one set of low-volume samplers was placed in houses 1 and 2 (control vs. treated) to take total suspended particulate (TSP) and particulate matter ≤10 μm in aerodynamic equivalent diameter (PM10). Also, 2 TSP samplers were placed in houses 3 and 4 at 2 different heights (0.28 and 0.71 m). These PM samplers were placed near a minimum ventilation fan (shown in Figures 2 and 3) 1.30 m (51 in.) away from the side wall. The collocated TSP-PM10 samplers placed inside houses 1 and 2 were 0.43 m (17 in.) apart at the sampling height of 0.71 m (28 in.). This set of sample collections was conducted for 9 sampling events (replicates). The PM samples were taken for a 3-h duration per sampling event.
For the second set of PM sample collections, a group of TSP samplers was placed in houses 1 and 2 (control vs. treated) to investigate PM vertical concentration variations. The heights of the sampler inlet heads (0.28, 0.71, 1.19, and 1.55 m) are labeled in Figure 3. This set of sample collections was conducted for 3 sampling events (replicates) and PM samples were taken for a 3-h duration per sampling event.
In addition to measurements of PM concentrations inside the houses, PM concentrations around the farm were also examined to estimate the contributions of PM from the farm to the surrounding ambient PM concentrations. For this set of PM sample collections, PM samples were taken outside of the minimum ventilation fan in house 1 as well as at 6 locations surrounding the farm (shown in Figure 4). Surrounding sampling locations were 30.5 to 61.0 m away from the houses. Due to space limitations, no samples were taken in either the north or south directions. All of the sampler inlet heads were at a height of 1.55 m (61 in.). Each sampling event lasted for 4 h with 4 sampling events (replicates) in total.
TSP and PM10 Concentration Determination—Direct Measurements
As indicated above, collocated TSP and PM10 samplers were used in this research for PM measurements. The low-volume TSP sampler was originally designed at Texas A&M University (Wang et al., 2005; Wanjura et al., 2005). The TSP or PM10 concentrations measured by low-volume TSP or PM10 samplers were determined by dividing the mass captured on the filter of the sampler by the total volume of air pulled through the sampler during the sampling period. The following equation was used for the concentration calculations:
Particle Size Distribution and Particle Size Distribution-Based PM10 Concentration Calculation
It has been reported (Buser et al., 2007a,b) that using the federal reference method (FRM) PM10 sampler to measure concentration of PM with a particle size distribution (PSD) characterized by a mass median diameter (MMD) larger than 10 μm will result in significant oversampling errors. The PM10 measurement may be up to 300% higher than true PM10 concentrations if the PM10 sampling head is operated within the designed FRM performance standards while sampling PM with a MMD of 20 μm and geometric SD (GSD) of 2.0. The PM10 oversampling errors are caused by the interactions between the samplers’ performance characteristics and the PSD of the sampled PM.
An alternative method to determine PM10 concentrations is to combine TSP concentrations and PSD analyses. Using this method, the PM10 concentration equals the TSP concentration times the mass fraction of PM10 obtained from the PSD (shown in equation ):
Particle size distributions of TSP samples were analyzed by the Center for Agricultural Air Quality Engineering and Science at Texas A&M University using a Coulter Counter Multisizer (Beckman Coulter Inc., Miami, FL). These size analyses gave a PSD in the form of particle volume (or mass) versus equivalent spherical diameter. The equivalent spherical diameter was converted to the aerodynamic equivalent diameter (AED) using the following equation:
Determination of NH4+ in PM
Particle NH4+ was analyzed using ion chromatographs (861 Advanced Compact IC, Metrohm Ltd., Basel, Switzerland). Filters were extracted by 3 portions of 5.0 mL of HPLC H2O (18 Ω) by sonication for 15 min each. Then, the extracted solutions (15 mL) were cleaned by passing through a syringe filter (0.2 um polytetrafluoroethylene membrane, Fisher Scientific, Pittsburgh, PA). The final volume of the combined extracts was made to be 15.0 mL. A Metrosep C2 100/4.0 analytical column (4 × 100 mm, Metrohm Ltd.) and an electrochemical detector were used in the cation analysis with isocratic elution at a flow rate of 1 mL/min. The eluent was 20 mM HNO3.
RESULTS AND DISCUSSION
PSD and PM10 Measurement Comparison
Figure 5 illustrates 2 sample PSD of PM from control and treated houses. As shown in this figure, both TSP samples from control and treated houses have very similar distribution profiles in the size range 3.0 to 60 µm. The average MMD and GSD of PSD in the control houses were 14.29 μm in AED and 1.91, respectively. The average MMD and GSD of PSD in the treated houses were 13.88 μm in AED and 1.93, respectively. These PSD gave 30.64% average PM10 mass fraction in the control houses and 32.72% average PM10 mass fraction in the treated houses, but t-test showed no significant difference between treated and control (P = 0.304).
The PM10 mass concentrations were calculated (equation ) based on PM10 mass fraction and TSP mass concentration. These calculated PM10 were compared with direct measurements of low-volume PM10 samplers and the results are shown in Figure 6. As shown in this figure, when PM10 concentrations are less than 10 mg/m3, calculated and measured values agree with each other very well. However, for high PM10 concentration samples, the PSD-based calculation results are much smaller than directed measurements in both treated and control houses.
For treated houses, the linear fits are:
There are both advantages and disadvantages for these 2 methods. For the PSD-based calculation method, TSP mass concentration and PSD information are required; PM mass fractions in any size ranges (e.g., PM10, particles with diameters ≤2.5 μm, and particles with diameters ≤2.5 to 10 μm) could be calculated based upon TSP concentration and PSD information. In this method, TSP sampler could provide more robust and accurate TSP measurements, as compared with FRM PM10 samplers for PM10 measurement. However, in the process of collecting TSP samples onto a filter for laboratory PSD analysis, PM is compacted onto a filter from a dispersed state in air. This collection process may change PSD. In addition, for filter-based PSD analysis, PM samples need to be extracted from a filter and dispersed in a liquid medium by mechanical stirring. In the sample extraction and dispersion process, some particles may dissolve or may be broken down in the medium, which might lead to changes in PSD (Tinke et al., 2009). On the other hand, for direct measurements of PM10 using the FRM PM10 sampler head, the interactions between the samplers’ performance characteristics and the PSD of PM will cause some degrees of the sampling errors (Buser et al., 2007a,b).
Further investigation is needed to better understand the differences in PM concentrations determined by these 2 methods (direct measurement vs. PSD-based method)
PM Concentration Inside Houses: Control Versus Treated
Comparisons of TSP and PM10 concentrations between treated and control houses are illustrated in Figure 7. The control TSP concentrations were the average of houses 1 and 4, and the treated TSP concentrations were the average of houses 2 and 3. As shown in Figure 7a, the treated house had higher TSP concentrations than the control houses. Paired t-test showed a significant difference between treated and control (P = 0.0012). The mean of the differences was 5.50 mg/m3. The PM10 concentrations were also compared (Figure 7b), and it was found that only 1 measurement showed higher PM10 concentration in treated houses than in control houses. This data point was identified as an influential observation (influential observations are the ones that affect the model statistics). The RSTUDENT residual (which measures the change in the residuals when an observation is deleted from the model) was greater than 3, but there was no identifiable reason to correct or omit the point. Tests both with and without this data point were conducted to examine how sensitive the results are to this point. Paired t-test did not show any difference between control and treated houses (P = 0.4915) with the influential observation. Without this point, the mean of the difference of PM10 concentrations in treated and control houses was −1.89 mg/m3 (P = 0.0006, indicating significant differences in the means between treatment and control). The test showed that PM10 concentrations in the control houses were significantly higher than those in the treated houses. This was inconsistent with TSP results. Based on the heterogeneous reactions theory, O3 can react with preexisting particles, and these reactions can affect the growth of these preexisting particles (Lee et al., 2004). In AFO environments where large amounts of NH3 and varieties of volatile organic compounds exist, it is well known that some of these compounds are very reactive with O3 and can form low-vapor-pressure products, which can either create new fine PM or condense onto preexisting PM (Went, 1960; Grosjean, 1992). In broiler houses, there are high levels of preexisting PM. One possible explanation for this observation is that the majority of the newly formed O3-oxidized low-vapor-pressure products condense onto preexisting PM instead of forming new fine particles, which could result in higher TSP concentrations observed in treated houses.
Particle NH4+ Concentration Comparison
The PM10 NH4+ concentrations from treated and control are shown in Figure 8. It was observed that the treated houses had much higher particle phase NH4+ concentrations than the control houses. The PM10 NH4+ concentrations in the treated houses ranged from 0.59 to 42.01 mg/m3 with mean = 17.49 mg/m3, and the PM10 NH4+ concentrations in the control houses ranged from 0.34 to 13.55 mg/m3 with mean = 4.42 mg/m3. At the time of this study, a field evaluation of ozonation for mitigating NH3 was simultaneously conducted on this broiler farm, and it was found that O3 has no effect on NH3 concentration (Wang et al., 2010). As stated above, through heterogeneous reactions, O3 can react with preexisting particles, and these reactions can alter preexisting particles’ chemical characteristics and surface properties. Preexisting particle surfaces become more hydrophilic and have polar side groups to their structure (Lee and Chan, 2007). These hydrophilic and polar particle surfaces promote NH3, water moisture, SO2, NOx, and organic compounds partitioning into particle phase by absorption or condensation. The dissolved or absorbed NH3 can be neutralized to ammonium salts [e.g., (NH4)2SO4, NH4NO3, NH4Cl, and NH4COOR; Renard et al., 2004] and these processes will result in high particle phase NH4+.
Vertical Variations in TSP Concentrations Inside the Houses: Control Versus Treated
In-house PM vertical concentration variations were also investigated and the results are shown in Figure 9. Four heights (0.28, 0.71, 1.19, and 1.55 m) were selected for the study: the lowest height (0.28 m) is about the broiler chicken height, and the highest height (1.55 m) is close to human breathing level. At broiler chicken height (0.28 m), TSP concentrations were 13 ± 3 mg/m3 in control houses and 17 ± 2 mg/m3 in treated houses. At human breathing height (1.55 m), TSP concentrations were 8 ± 4 mg/m3 in control houses and 7 ± 2 mg/m3 in treated houses. As shown in Figure 9, TSP concentrations at all heights except the top one were significantly higher in house 2 (treated) than in house 1 (control). In both houses, the results indicated substantial concentration gradients at different heights. The TSP concentration decreased as height increased. This variation in TSP concentration suggests the effect of ventilation fans and chicken activity on the vertical distribution of PM concentration. As shown in Figure 9, chickens and farm workers are exposed to different PM concentrations in the same facility. Knowledge of PM concentration spatial distribution is very important for human exposure and animal welfare studies in the future.
TSP and NH4+ Concentration Variations in the Farm Vicinity
As shown in Figure 4, six vicinity and 1 sampling location were selected to investigate spatial PM concentration variation and fate and transport of the emitted PM in the farm vicinity. The TSP concentrations at these locations are listed in Table 1. In general, the sampling location at the emission source (4.6 m away from a minimum fan) has the highest TSP concentrations (ranging from 0.84 to 5.81 mg/m3). However, there were 3 exceptional observations (Table 1) in which concentrations at surrounding area of the houses were higher than those at the emission source. In test 1, concentration at the northeast location was 6.96 mg/m3, 21.60 mg/m3 at the northwest location, and 5.81 mg/m3 at the source. In test 3, concentration at the east location was 10.97 mg/m3 and was 3.04 mg/m3 at the source. It is suspected that these high ambient concentrations were due to road dust as well as windblown dust from the surrounding peach orchard. No other emission sources were noticed within a 1,600-m radius around this farm.
Total suspended particulate (TSP) concentrations (mg/m3) at 7 sampling locations1 (see Figure 4 for locations)
1NE = northeast; E = east; SE = southeast; SW = southwest; W = west; NW = northwest.
2One TSP sampler was placed 4.6 m (15 ft) away from a minimum fan outside house 1 with sampler head at 1.55-m (61-in.) height (see Figure 4).
3Concentrations at surrounding area of the houses were higher than those at the emission source.
Table 1 and Figure 10 also indicate that downwind concentrations (ranging from 0.21 to 2.26 mg/m3) were higher than upwind concentrations (0 to 1.10 mg/m3), with the highest concentration at the source (5.81 to 5.70 mg/m3). This observation suggests that the TSP concentration faded significantly in a very short distance.
The NH4+ concentrations in ambient TSP samples are shown in Figure 11. Although the location at the source (H1F1, see locations in Figure 4) had the highest gaseous NH3 concentration among all locations, TSP samples at location H1F1 did not show higher levels of particle phase NH4+ concentration than those at the ambient stations. Samples from southeast had the highest median NH4+ concentration (0.38 mg/m3), and samples from northwest had the lowest median NH4+ concentration (0.12 mg/m3).
This study evaluated the effect of ozonation technique on PM concentrations in AFO. It was found that treated houses had higher TSP concentrations than control houses. It was also observed that particle phase NH4+ (PM10 NH4+) concentrations were higher in treated houses than those in control houses. The TSP concentrations varied with height above the floor in both treated and control houses. The concentration decreased as height increased. The TSP samples from the farm vicinity showed higher concentrations downwind than upwind, but for TSP NH4+ concentrations, no significant difference was observed among the different locations. This study discovered that direct application of the ozonation technique in AFO has no beneficial effects for PM control.
This project was sponsored by the Animal and Poultry Waste Management Center at North Carolina State University. We thank John D. Wanjura and Brock Faulkner, members (at the time) of the Center for Agricultural Air Quality Engineering and Science at Texas A&M University for supplying TSP samplers. We also thank Zifei Liu and Zihan Cao in the Department of Biological and Agricultural Engineering at North Carolina State University for their help with ion chromatograph analysis.