Indoor Concentration Distributions of Ammonia and Sulfur-Based Odorous Substances According to Types of Laying Hen Houses in South Korea

Abstract

In South Korea, environmental complaints related to livestock odors continue to increase, and various efforts are underway to overcome them. An objective of this study is to monitor indoor concentrations of ammonia and sulfur-based odorous substances emitted from laying hen houses in South Korea through on-site visits for one year to understand their temporal emission patterns. The highest concentration was found in ammonia (NH₃), at 6.92 ppmv, followed by hydrogen sulfide (H₂S), at 8.98 ppbv. The concentrations of methyl mercaptan (CH₃SH), dimethyl sulfide (DMS), and dimethyldisulfide (DMDS) ranged from sub ppbv to 10 ppbv. In general, there was no consistent concentration distribution of ammonia and sulfur-based odorous substances in laying hen houses between those with forced ventilation and natural ventilation. Regarding the seasonal distribution of odorous compounds, their concentrations in winter season (December to February) when the ventilation rate in laying hen houses decreased were generally higher than those in the summer season (June to August) when the ventilation rate in poultry buildings was relatively high, which is applied to properly maintain the thermal environment in laying hen houses. The limitation of this study is that unexpected conditions such as clearance of laying hen houses, chicken shipments, and disorders of exhaust fans were not controlled for intentionally due to on-site investigations.

1. Introduction

As livestock farming has become more intensive and corporatized in a relatively limited area, proper treatment of large amounts of livestock manure and the prevention of odor problems have become essential prerequisites for sustainable livestock farming. Odor complaints are constantly increasing due to residents’ desire to improve their quality of life and the gradual decrease in the spatial distance between urban and rural areas, and in this regard, the government has been implementing a strengthened Korean Odor Prevention Act [1] since February 2005 by separating the odor-related part from the existing Air Environment Protection Act.

The domestic livestock industry is transitioning from a small-scale industrial form to a large-scale corporatized form in order to increase livestock productivity, and the number of livestock has not decreased significantly compared to the past [2]. It is true that the environmental conditions for livestock have improved considerably due to these changes, and the productivity indicators of livestock have tended to increase year by year. However, if air pollutants such as odors, dust, and suspended microorganisms are emitted from the indoor environment of livestock farms to the outside under conditions that are not adequately controlled, they can cause environmental health problems such as odor generation [3] at the micro level and climate change due to ozone depletion [4] and the airborne transmission of foot-and-mouth disease and avian influenza viruses [5] at the macro level. In South Korea, in particular, complaints about livestock odors are one of the biggest social threats to the livestock industry.

Among livestock facilities, laying hen houses are known to produce odors that are higher in concentration, intensity, and offensiveness compared to odors emitted from typical industrial and residential facilities [6,7]. However, in the case of domestic poultry facilities operating under poor economic conditions, low-cost, low-efficiency odor control technologies, such as injecting microbial additives and chemical solutions to remove odorous substances into the feed or spraying them indoors, are applied in a very simple way, so that the odorous substances generated inside the poultry house are discharged to the outside under almost uncontrolled conditions.

In developed countries such as the U.S. and Europe, odor-causing substances emitted from chicken houses have been evaluated for their health hazards through occupational health monitoring for workers in chicken houses [8,9,10], and in terms of air quality, emission coefficient calculation studies [11,12,13,14,15] have been conducted since the early 1990s to establish appropriate separation distances through the application of odor diffusion models to resolve odor complaints from residents living near rice mills. However, in Korea, even basic research, such as obtaining field measurements of indoor concentration levels of odor-causing substances generated in poultry houses, has rarely been conducted.

Therefore, the purpose of this study is to estimate the indoor concentration distribution characteristics of ammonia and sulfur-based odorous substances, which are considered to be the main factors in the formation of livestock odor, reflecting the type of laying hen house and climatic conditions, via field survey, and to provide basic data for reflecting environmental and occupational health policies related to laying hen house odor.

2. Materials and Methods

2.1. Subject

Air samples were collected for the analysis of ammonia and sulfur-based odorous substances through monthly on-site visits to two poultry farms located in the Jeju area (Figure 1) for a total of one year from July 2020 to June 2021. The reason why poultry farms located in the Jeju region were selected for investigation is because the incidence of infectious diseases related to chickens, such as avian influenza, was relatively low compared to the mainland, so it was relatively easy for outsiders to enter the farm for field investigations. In addition, in the case of Jeju, a clean area, the concentration of external air pollutants is relatively low, so the level of inflow into the laying hen house is estimated to be quite minimal. The specifications of the laying hen houses surveyed in this study are shown in

Table 1. Profile of the chicken houses investigated in this study.

Laying Hen House	Manure Collection System	Ventilation Mode	Housing Head (N)	Size (m) (W × L × H)	Fan
					N	Location
W farm	Treatment with conveyer belt	* F.V. (enclosed type)	19,000	50.0 × 8.0 × 8.5	2	Side wall
Y farm	Treatment with conveyer belt	† N.V. (winch-curtain)	5700	51.0 × 6.4 × 9.0	-

*: Forced ventilation; †: Natural ventilation.

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2.2. Measurement

Concentrations of ammonia and sulfur-based odorous substances were measured at a central location 1 m above the floor in the middle hallway of the laying hen house under moderate weather conditions, which is in accordance with Odor Prevention Act of South Korea. The air samples were taken once every hour between 9 am and 5 pm to maintain the objectivity of monthly data. Thus, the total number of samples for one laying hen house was 108 (1 central location × 9 times per day × 12 months). If a compound was not detected, the mean values were calculated with half of the value between 0 and the LOQ.

The measurement and analysis of ammonia and sulfur-based odorants were performed according to the Korean Odor Process Test Method [1]. Analyses of ammonia were performed according to the methods recommended by NIOSH (National Institute for Occupational Safety and Health). Using an air sampling pump (Model 71G9, Gilian Instrument Corp., Newark, NJ, USA) adjusted to 2.0 L/min of flow rate, air was collected for 10–20 min into an all-glass impinger 30 (Ace Glass Inc., Vineland, NJ, USA) including the absorption fluid (100.1N-H₂SO₄ solution) (Figure 2). After sampling, the absorption fluid was analyzed by a UV-spectrophotometer (UV-1601, SHIMADZU, Kyoto, Japan) whose operational specifications are shown in

Table 2. Operation condition for analyzing ammonia in laying hen houses.

Analyzer	Variables	Analytical Conditions	LOD	LOQ	Calibration
Uv-vis spetrometer (s-3100, scinco, Seoul, Republic of Korea)	Detector	Uv-vis	0.01 ppmv	0.03 ppmv	Every time in analyzing
	Wavelength	640 nm

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To measure the concentrations of sulfur-based odorous substances (H₂S, CH₃SH, DMS and DMDS), air was sampled for 5 min into a black layered tedlar sample bag (10 ℓ, SKC, Eighty Four, PA, USA), which was connected with a teflon septum fitting to a low-volume air sampler (No. 800519, Gilian, USA) with a flow rate of 1.5~2.0 L min⁻¹ (Figure 2). After air sampling, the tedlar bags were immediately transported to the laboratory and analyzed within 24 h, which refers to the effective time that the air sample in the tedlar bag can be analyzed. For quality assurance/quality control (QA/QC), the limit of detection (LOD) and relative standard deviation (RSD) were calculated and reviewed. In this case, we set the goal of QA/QC related to the degree of precision and calibration curve with R2 > 0.98 and RSD (%) within 10%, respectively. Detailed information of the thermal desorption unity (U-UNITYe, Markes international, Bridgend, UK) and GC/PFPD (CP-3800, Varian, Palo Alto, CA, USA) is described in Table 2 and

Table 3. Operation condition for analyzing sulfur-based odorous substances (H₂S, CH₃SH, DMS, and DMDS) in laying hen houses.

	Analytical Conditions
Thermal Desorber (Unity + Airserver: Markes Ltd., Bridgend, UK)	Sampling flow	50 mL/min
	Sampling time	10 min
	Cold trap	Hydrogen sulfide
	Cold trap low temperature	−15 °C
	Cold trap high temperature	250 °C
	Cold trap hold time	5 min
GC/FPD (GC-2010, Simadzu, Kyoto, Japan)	Column info	Varian CP-SIL 5CB (60 m × 0.32 mm × 5 µm)
	Initial temperature	50 °C (7 min)
	Temperature Rate	10 °C/min to 280 °C
	Final temperature	280 °C (5 min)
	Detector temperature	300 °C
	H2 flow	60 mL/min
	Air flow	70 mL/min
	LOD	0.001 ppbv
	LOQ	0.003 ppbv
	Calibration	Every time in analyzing

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3. Results

3.1. Ammonia and Sulfur-Based Odorous Substances: Monthly Concentration Distribution

Figure 3 shows the change trend in monthly indoor concentrations of ammonia and sulfur-based odorous substances by type of laying hen house, measured during monthly field visits for one year from July 2020 to June 2021. The monthly indoor concentration distributions of odorous substances according to the type of laying hen house are as follows.

The mean concentration and range of ammonia in the laying hen house (W farm) operated by forced ventilation system with a conveyor belt for removing manure were analyzed to be 2.87 (0.51~11.48) ppmv. The average concentrations and ranges of sulfur-based odorous substances were 4.57 (1.93~8.68) ppbv for hydrogen sulfide, 1.23 (n.d.~4.19) ppbv for methyl mercaptan, 1.33 (0.09~4.51) ppbv for dimethyl sulfide, and 0.02 (n.d.~0.18) ppbv for dimethyl disulfide, respectively.

On the other hand, in the case of Y farm, which is operated by a natural ventilation system with a conveyor belt for removing manure, the mean concentration and range of ammonia were 1.64 (0.51~3.19) ppmv. The average concentrations and ranges of sulfur-based odorous substances were 6.38 (2.01~18.76) ppbv for hydrogen sulfide, 0.82 (n.d.~4.89) ppbv for methyl mercaptan, 1.12 (n.d.~5.69) ppbv for dimethyl sulfide, and 0.01 (n.d.~0.12) ppbv for dimethyl disulfide, respectively.

As compared to the regulatory standards of the Korean Odor Prevention Act (ammonia, NH₃: 2 ppmv; hydrogen sulfide, H₂S: 60 ppbv; methyl mercaptan, CH₃SH: 4 ppbv; dimethyldisulfide, DMS: 50 ppbv; and dimethyldisulfide, DMDS: 30 ppbv), the results showed that ammonia exceeded the regulatory standards in January, October, November, and December for W farm and in January, May, July, and November for Y farm. However, all four sulfur-based odorants did not exceed the regulatory standards, regardless of the month.

3.2. Ammonia and Sulfur-Based Odorous Substances: Seasonal Concentration Distribution

The change trend in seasonal indoor concentrations of ammonia and sulfur-based odorous substances by type of laying hen house is shown in Figure 4. Here, the seasons are divided into spring (March to May), summer (June to August), fall (September to November), and winter (December to February). Representative values for each season are the average of monthly data measured over the three months corresponding to each season. The results of seasonal indoor concentrations of odorous substances measured in the two surveyed laying hen houses are as follows.

The average and range of the measured data for the two hen houses (W and Y farm) are as follows. The mean concentration and range of ammonia were 1.39 (1.32~1.48) ppmv in spring, 1.36 (0.81~1.88) ppmv in summer, 2.21 (2.14~2.27) ppmv in fall, and 4.52 (2.11~6.92) ppmv in winter, respectively. The mean concentration and range of hydrogen sulfide were 5.51 (5.46~5.51) ppbv in spring, 3.99 (2.44~5.54) ppbv in summer, 3.57 (2.59~4.54) ppbv in fall, and 7.07 (5.14~8.98) ppbv in winter, respectively. The mean concentration and range of methyl mercaptan were 1.66 (1.20~2.12) ppbv in spring, 0.34 (n.d.~0.71) ppbv in summer, 0.27 (n.d.~0.56) ppbv in fall, and 1.39 (0.55~2.24) ppbv in winter, respectively. The mean concentration and range of dimethyl sulfide were 2.16 (0.98~3.34) ppbv in spring, 0.45 (0.13.~0.78) ppbv in summer, 0.73 (0.41~1.05) ppbv in fall, and 1.30 (n.d.~2.63) ppbv in winter, respectively. In the case of dimethyl disulfide, the average concentration and range were 0.09 (0.06~0.11) ppbv only in fall, and it was not detected in spring, summer, and winter.

4. Discussion

Regardless of the type of hen house and the time of measurement, the indoor concentration levels of each odorous substance were found to be the highest for ammonia, measured at the ppmv level, followed by hydrogen sulfide among sulfur-based substances, and the remaining substances at low levels of ppbv. In general, the concentration of indoor odorous substances by hen house type according to the difference in ventilation method was analyzed to be not significantly different between laying hens with natural ventilation using winch curtains and laying hens with forced ventilation using side wall exhaust fans.

In terms of monthly and seasonal concentration trends, it was found that the winter season (December–February), during which the ventilation rate decreased, resulted in higher concentrations of odorous substances inside the barn than the summer season (June–August), when the ventilation rate was relatively high, while the spring season (March–May) and fall season (September–November) were similar. Based on the results of this measurement, both ammonia and sulfur-based odorous substances were identified as displaying a significant variation in concentration levels among barn types, months, and seasons, which is presumed to be a result of changes in various environmental factors on the day of measurement due to the nature of the field survey. However, the reason for the relatively high ammonia concentration in January at Farm W in the measured data is that the ventilation fan was temporarily not working at the time of the field measurement, and the air inside the barn could not be discharged smoothly to the outside. Therefore, these data are not typical of the ammonia concentration in the barn.

Based on the results obtained from this study, the concentration of ammonia was the highest, followed by hydrogen sulfide, both of which are at a ppm level. However, the odor threshold of the two substances is quite different. The odor threshold of H₂S is low, and the lower chemical concentration can cause greater odor. Therefore, the simple comparison of the chemical concentration of pollutants is of limited significance for practical guidance.

In other countries, many researchers have already initiated and reported studies on the quantification of toxic gasses such as ammonia and hydrogen sulfide in chicken houses by field measurement [13,14,16]. Based on their findings, the large variation in concentrations of odorous compounds among chicken houses was attributed to the observation that the ambient air temperature and relative humidity was measured differently among chicken houses. They play a role in affecting volatilization degree of odorous compounds emitted from chicken houses [17].

Phenolic substances such as p-cresol, skatole, and indole have also been suggested by some international researchers as major contributors to odor generation in broiler houses [7,18]. In addition, it has been reported that exposure to these substances above the permissible level in the broiler house environment causes decreased productivity in chickens and respiratory system diseases such as asthma, rhinitis, and bronchitis in poultry workers [19], However, since these substances are not regulated in the current domestic odor prevention legislation, a study on the rationalization of indoor environmental standards for broiler house odor management should be considered in the future to objectively reflect the results of qualitative analysis of broiler house odor.

A limitation of this study is that the statistical correlation between the temperature and relative humidity, which are the main factors that determine the intensity of the odor generation, and the concentration of odorous substances in the laying hen houses could not be determined in this study because the temperature and relative humidity were not monitored simultaneously. Therefore, further research is required to identify the correlation between the concentration of odor-causing substances and the temperature and relative humidity in the laying hen house. Furthermore, the real-time monitoring methods applied to air pollutants such as NO, NO₂, SO₂, and PM_2.5 should be utilized to understand the exact pattern of odor occurrence. For sulfur-based odorants such as CH₃SH, DMS, and DMDS [20,21], however, it is currently not possible to detect them through sensing. Therefore, it is necessary to develop high-performance sensors for their real-time monitoring in the future.

Although this study has limitations due to the small sample size of only two henhouses, it is the first study to monitor the indoor concentrations of ammonia and sulfur-based odors over a 12-month period during field visits to representative farms with mechanical and natural ventilation, and the data can be used as a basis for environmental and occupational health policy preparation.

5. Conclusions

Regardless of the type of system and the time of measurement, the indoor concentration levels of each odorous substance in Korea were found to be the highest for ammonia, measured at the ppmv level, followed by hydrogen sulfide among the sulfur-based substances, and the remaining substances were observed at very low levels of ppbv. In terms of the indoor concentration distribution of odorous substances according to the type of ventilation system, it was found that there was no consistent change in the internal odor concentration distribution between the windowless system with forced ventilation and the winch system with natural ventilation, and the concentration difference varied by substance. In terms of monthly and seasonal concentration trends, it was found that the concentration of odorous substances inside the stairwell was higher in winter (December to February), when the stairwell ventilation rate decreased, than in summer (June to August), when it was relatively high, and similar levels were observed in spring (March to May) and fall (September to November).