Are Adaptation Measures Used to Alleviate Heat Stress Appropriate to Reduce Ammonia Emissions?

Abstract

The emission of ammonia (NH₃) is predominantly caused by agriculture, especially by livestock keeping. The health effects of NH₃ and the related formation of particulate matter are the reasons for solid efforts to reduce their ambient concentrations. In addition, the impact of global warming on livestock is increasing due to heat stress, likely also increasing NH₃ emissions. Therefore, adaptation measures are under discussion to reduce the heat stress of animals inside livestock units. Because of the relationship between temperature increase and NH₃ release, the impact of the adaptation measures to cool the indoor air of livestock units (three different energy-saving air preparation systems, an inversion of the feeding and resting times by half a day, a reduction of the stocking density and doubling the maximum volume flow rate) was investigated. The NH₃ release was calculated by the following predictors: indoor air temperature; ventilation rate describing the turbulence inside the livestock building; and the diurnal variation caused by the animal activity. These parameters were calculated by a simulation model for the indoor climate of livestock buildings. The monthly mean of the NH₃ emission for several adaptation measures, which were applied to reduce heat stress, were compared with the emission of a reference building for 1800 fattening pigs, divided into nine sections with 200 animals each for an all-in-all-out production cycle to calculate the mitigation potential. The higher the cooling power of such adaptation measures, the higher the mitigation potential for NH₃. In particular, those adaptation measures which cool the inlet air (e.g., cooling pads reduce the emission by −2%, earth-air heat exchangers by −3.1%) show the best performance to mitigate the NH₃ emission of livestock buildings.

1. Introduction

Ammonia (NH₃) and particulate matter ((PM) fine solid particles, and liquid droplets) are pollutants with implications on the environment, which range from the acidification of terrestrial and the eutrophication of aquatic environments, to impacts on biodiversity in general [1]. Further aspects are the direct implications on animals [2] and human health [3]. The most-reported acute implications of NH₃ exposure for both are nasal lavage (liquid acquired from the nose), lung function and bronchial responsiveness, eye, nose, and throat irritation, headache, nausea, diarrhoea, hoarseness, sore throat, cough, chest tightness, nasal congestion, palpitations, shortness of breath, stress, drowsiness, and alterations in mood [4,5]. NH₃ is an important precursor of fine particulate matter formation in the atmosphere [6,7,8,9,10]. It is important to highlight the link between PM_2.5 and NH₃ emissions. Between 30% and 50% of all PM_2.5 is a direct result of NH₃ emissions [11,12,13]. In 1990, nitrogen accounted for 30% of global PM_2.5 formation, increasing to 39% in 2013 [14]. It was found that a reduction of NH₃ emissions by 50% leads to a 24% reduction of total PM_2.5 concentrations during winter, mainly driven by the reduced formation of ammonium nitrate [15]. NH₃ is one of the airborne pollutants, which cannot be reduced in a comparable amount to many other European pollutants, such as SO₂ in the 1980s. Thus, for Europe, it has been shown that NH₃ emissions have dropped by 23% between 1990 and 2015, although between 2014 and 2015, emissions increased by 1.8% [16]. Between 2000 and 2015, the emissions decreased by 8%. In Austria, however, a positive trend (an increase of NH₃ emissions from 1990 to 2016 by +3%) was observed [17].

In Austria, most NH₃ emissions are caused by agricultural activities (95%), with 47% for livestock and manure storage, 43% for manure spreading, 8% for fertiliser, and 2% for pasture and other activities. Overall, about 62 kt NH₃ were emitted in 2011 [18]. The Austrian emission was 57.2 kt in 2005, with a continuous increase to 64.6 kt in 2017. According to the National Emissions Reduction Commitments (NEC guideline) [19], a reduction of 12.3% should be achieved in 2020 (in relation to 2017) to reach the goal of 50.3 kt. For 2020 the emission was determined with 65.42 kt in reality. For all years from 2020 to 2029, the EU will have to reduce its total NH₃ emissions by 6% compared with 2005, and by 19% for all years from 2030 onwards [17].

All negative impacts of the ambient concentrations of NH₃ and the related secondary PM_2.5 formation are human premature deaths and health-related expenses [3,20,21,22,23]. For the EU, about 274,000 premature deaths per year, i.e., 6% of all deaths, are due to exposure to PM_2.5 and ozone [24]. On the basis of the human premature death rate, the threshold for the annual risk exposure level for PM_2.5 was downward adjusted to 2.4–5.9 μg/m³ from a previous level of 5.8 to 8.8 µg/m³ [25].

In the EU, the cost range for damages due to NH₃ emissions lie between EUR 70 and 320 billion, equivalent to EUR 150–750 per capita, of which about 75% are related to health damage and air pollution. Related to NH₃, the mean costs for the EU are estimated at EUR 9.5/kg NH₃ with a high variation in between the countries (countries with the three highest and four lowest costs (EUR/kg NH₃) are: Belgium 36, Luxembourg 30, The Netherlands 27; Lithuania 2, Finland 3, Estonia 3, Ireland 3. For Europe, the health costs from secondary ammonium particles were estimated at EUR 2–20/kg nitrogen [22]. For China, the societal benefits of a 50% reduction of NH₃ emissions with costs of USD 6–11 billion were estimated to amount to USD 18–42 billion [26]. The marginal abatement cost of ammonia emission is only 10% of that of nitrogen oxides emission globally to mitigate PM_2.5 air pollution [14].

Since NH₃ emissions have been shown to be climate sensitive, with NH₃ emissions increasing with increasing ambient temperatures, the global change effect cannot be neglected in the future. An empirical estimate suggests that an assumed warming of 5 K would increase NH₃ emissions by 42% on average (in a range of 28% to 67%, [27]). The impact of climate change (warming of 0.23 K per decade inside livestock buildings) on the NH₃ emissions of livestock buildings was estimated to increase by 1.6% per decade [28]. Using long-term climate simulations, Geels et al. [29] showed that the climate change impact on NH₃ emissions and resulting secondary aerosol formation will increase chronic mortality by up to 4% until 2080. This means that the expected global warming will counteract the efforts to reduce agriculturally emitted NH₃ to improve air quality. For the 2050s, the NH₃ emissions from confined livestock buildings, predominantly used for fattening pigs and poultry, are expected to increase by about 15 to 20% (relative to 2007) due to the increase in temperature [30]. Skjøth and Geels [31] investigated the sensitivity of agricultural NH₃ emission categories due to global warming, showing the highest sensitivity for livestock buildings and manure storage, manure handling, the application of fertiliser, and grazing animals. They expect an emission increase up to 40% due to the global warming signal.

Under the assumption of a constant linear trend of anthropogenic warming until 2050, NH₃ emissions from livestock buildings will increase by about 11% between 1981 and 2050. For the storage of manure, Aarnink and Elzing [32] found a 10% increase of the emission rate of NH₃ for an increase of the storage temperature of 1 K.

The release of NH₃ can be modified by several predictors. The following predictors are closely related to the keeping of animals: physical activity with a distinct diurnal variation; the size of the defecation area, which is the main release surface; the nitrogen content of the feed; the bedding material; and the pH value of manure [26,33,34,35,36,37,38,39]. Some of these predictors can be directly used to mitigate the NH₃ release, e.g., reducing the size of the fouling surface by offering a well-accepted and comfortable solid lying area, or by a restricted dietary crude protein content.

The main microclimatic predictors for the NH₃ release are temperature, the air velocity above the release surface, and the ventilation regime inside the livestock building [40,41,42,43,44,45]. These predictors are closely connected to the indoor microclimate of the livestock building. Measures which alleviate heat stress (HS) can lead to a side-effect by reducing the NH₃ emission. Cooling the inlet air can lead to a reduction of the ventilation rate from the livestock building [46].

Tremendous efforts will be needed in the upcoming decade to reduce the NH₃ emission from agricultural activities in a proposed range of about 25%. In this respect, we analyse the potential of selected adaptation measures, which alleviate HS inside livestock buildings for fattening pigs (body mass 30 to 120 kg, mechanically ventilated) to also reduce the NH₃ emission. With a simulation driven by meteorological data (1981 to 2017), the indoor climate and the related release of NH₃ are calculated for a reference building on a business-as-usual basis, and compared to that of seven adaptation measures to reduce heat stress.

2. Data and Methods

2.1. Simulation of the Indoor Climate of Confined Livestock Buildings

Meteorological data are needed on an hourly basis (air temperature and relative humidity) for the calculation of the indoor climate and the related emissions of odorous substances and NH₃. The Austrian Meteorological Service ZAMG (Zentralanstalt fürMeteorologie und Geodynamik, Vienna, Austria) provided measurements for the weather station close to the city of Wels (48.16° N, 14.07° E) for the time period 1981 to 2017.

The simulation of the indoor climate was performed by a steady-state model developed by Schauberger et al. [47,48], which calculates the thermal indoor parameters (air temperature, humidity) and the ventilation flow rate. The simulation is driven only by meteorological data. The thermal environment inside the building depends on the livestock (sensible and latent heat release), the thermal properties of the building (sensible heat loss), and the ventilation system and its control unit, which controls the ventilation rate by means of the indoor air temperature as the control parameter. The ventilation system is characterised by the minimum ventilation rate (wintertime, to ensure not only the required air quality but also to avoid cold stress) and the maximum ventilation rate (summertime, to remove the sensible heat of the animals to prevent HS). The core of the model is based on the sensible heat balance of a livestock building [46,47,48,49]. The model calculations were performed for a representative livestock building for fattening pigs (body mass between 30 and 120 kg, mechanically ventilated) in central Europe for 1800 heads, divided into nine sections with 200 animals each for an all-in-all-out production cycle. This conventional livestock building for fattening pigs used as a business-as-usual scenario is called reference building REF. Fattening pigs were selected because they are more sensitive to heat stress than piglets and are a relevant source for NH₃ in the national inventory in the range of 17% [18].

The seven adaptation measures to reduce HS for the animals were applied to the entire livestock building with 1800 pigs. The outcome of the simulation of the seven adaptation measures was compared to that of the reference building REF.

2.2. Ammonia Emission and the Mitigation Potential

In general, the airborne NH₃ emission rate of a livestock building is calculated by a body mass-specific emission factor e_0, which is related to one animal place (AP). The reference NH₃ emission rate is an annual mean value with e_NH3,0 = 3.64 kg a⁻¹ per AP, which is selected from the German VDI standard [50].

The NH₃ release is modified by the indoor climate (temperature, ventilation rate, and time of the day) of the livestock building [42,44]. This modification is considered by the release modification factor R according to e = e₀ R. R is calculated on the basis of the indoor air temperature T_i, the ventilation rate V, and the physical activity of animals as a function of daytime t [28,44,49]. The release modification factor R is thus given by:

$$R=\exp \left(0.0314\left(T_i-T_R\right)\right)V_n^{0.318}\left(1+0.25\sin \left(\frac{2\pi }{24h}\left(t-6h\right)\right)+\frac{0.25}{3}\sin \left(\frac{2\pi }{24h}3\left(t-6h\right)\right)\right)$$

with the indoor temperature T_i (°C), the reference temperature T_R = 20 °C, the normalised ventilation rate V_n = V/V_d, calculated by the ventilation rate per animal place V, normalised to unity by V_d = 200 m³ h⁻¹ per AP, and the time of the day t. The ventilation rate V and the indoor temperature T_i are calculated by the indoor simulation. The factor R is calculated on an hourly basis and aggregated to monthly mean values. The relative modification of the NH₃ emission MOD of a certain adaptation measure (AM) is calculated by the monthly mean of the release modification factor R_i of this AM and the release modification factor R_REF for the reference case REF, with a business-as-usual scenario according to MOD_i = 1 − R_i/R_REF. or as a percentage MOD_i = 100 (1 − R_i/R_REF).

2.3. Adaptation Measures to Reduce Heat Stress

In total, seven AMs are investigated. First, three different energy-saving air preparation systems [51] comprising: (1) direct evaporative cooling by cooling pads (CP); (2) an indirect evaporative cooling by the combination of cooling pads with a regenerative heat exchanger (CPHE) to reduce the humidity load caused by the evaporative cooling; and (3) an earth-air heat exchanger (EAHE), using the ground as heat storage. The fourth AM assumes an inversion of the feeding and resting times by half a day to move the maximum heat release of the animals to night-time with a lower inlet air temperature INV. Two further AMs modify the internal heat load of the livestock building by a reduction of the stocking density (SD) to (5) 80% of the design value (SD80%) and (6) to 60% (SD60%). The last AM (7) affects the design value of the ventilation system by doubling the maximum volume flow rate (VENT) to increase the removal of the sensible heat released by the animals. Technical details on all seven AMs are discussed in Schauberger et al. [52].

3. Results

The primary goal of the seven AMs is the reduction of HS. The efficacy of HS reduction as a ratio of the heat stress of a certain AM, and the reference scenario REF, is shown in Figure 1, displaying the annual sums of the HS parameter P_T25 for the reference scenario REF and all seven AMs. The HS parameter P_T25 gives the portion of time (h/a) above the threshold value of T = 25 °C. The slope of a specific AM goes proportional to the reduction factor. The flatter the regression, the higher the efficacy. For the line of identity, the indoor situation is identical to the HS inside the reference building without an AM, which means that no reduction of HS can be expected. The best performance is shown for the energy-saving air preparation AMs for cooling the inlet air (EAHE, CP, and CPHE) followed by doubling the ventilation rate VENT, the inversion of the resting and activity periods INV and the reduction of the stocking density SD60% and SD80%.

Even if the HS index P_T25 quantifies the performance of the AMs with respect to HS, the modification of the indoor climate for the entire year is not represented by this value. Therefore, the two parameters, indoor air temperature and volume flow rate of the ventilation system, were selected to describe the indoor climate for all months. These two parameters are also predictors for the NH₃ release. The volume flow rate is used as a proxy for the air velocity close to the release surface for NH₃. The third predictor is animal activity, which does not show any dependence from the indoor climate.

The difference of the monthly mean indoor temperature over a year between the reference building REF and the seven AMs is shown in Figure 2. Due to the fact that the temperature difference is analysed, the trend over the 37 years of simulation is widely eliminated. SD80% and INV show almost no reduction of indoor temperature during summer, followed by a slight decrease by SD60%. The temperature reduction for the energy-saving air preparation measures (CP, CPHE, and EAHE) is distinctly higher for the summer months compared to the other AMs except for VENT. VENT shows a similar summertime temperature reduction to CP and CPHE but less variation. EAHE indicates not only a reduction of the indoor air temperature in summer but also an increase during wintertime, caused by the use of the soil as a heat source. The annual mean value of the temperature difference is shown in the lowest right graph. This demonstrates the considerable variation of temperature differences for the EAHE scenario again.

In Figure 3, the difference of the ventilation rate per animal place between the reference building REF and the application of the AMs is shown. During summertime, the slight reduction of the heat release of the animals by SD80% and SD60% also causes a slight decrease of the ventilation rate. If INV and especially VENT are used to reduce HS, the ventilation rate per animal place is increased during the summer months. CP and CPHE show only an increase in the summertime ventilation rate variability compared to the winter months without a specific trend. Using EAHE, the warming of the inlet air during wintertime causes an increase of the ventilation rate. This side effect causes an amelioration of the air quality. The reduction of the ventilation rate difference to the REF scenario during the summer months is caused by the fact that the sensible heat release of the animals is reduced, which causes an abatement of the ventilation rate as well.

The relative modification of the NH₃ emission MOD (monthly mean values for the period 1981–2017) caused by the two predictors indoor air temperature and volume flow rate, is depicted in Figure 4. MOD is shown by colour-coded data points with red for a relative increase of ammonia emission and blue for a reduction. For all AMs, both an increase and a decrease in NH₃ emissions can occur. For SD80%, SD60%, INV, and VENT, the difference in the ventilation rate has a more significant impact on the NH₃ emission than the indoor air temperature difference. Therefore, the highest variation of NH₃ emissions is found for VENT. For CP and CPHE, the variation in NH₃ emissions is dominated by the indoor air temperature differences. The widest spread of NH₃ emissions is found for the EAHE, equally caused by both predictors: A temperature increase of up to 3 K for wintertime and a decrease of about −4 K for summertime (Figure 2), an increase of the ventilation rate of about 8 m³ h⁻¹ for wintertime (due to higher inlet air temperature) and a decrease of –22 m³ h⁻¹ for summertime due to lower inlet air temperature (Figure 3). These characteristics of the EAHE result in a decrease of the NH₃ emission of 19% for the summer months due to a lower indoor temperature (Figure 2) and a lower ventilation flow rate (Figure 3), and an increase of up to 14% for the winter months caused by a higher indoor temperature and a corresponding higher ventilation flow rate (Figure 5).

In Figure 5, the relative difference in the ammonia emission between the REF scenario and a specific AM is shown in the form of violin plots as a time course over the months. Most of the AMs show a reduction of the NH₃ emission, especially for the spring and summer months. VENT and EAHE show a distinct increase for some of the months. The growth of the NH₃ emission by VENT is caused by the rise of the air velocity close to the release surface of NH₃ (e.g., slatted floor, slurry surface) during the summer months. During the cold period, the ventilation rate stays unchanged (see Figure 3, VENT), which means that the mean of the NH₃ emission shows no change as well. The increase of the ventilation rate during the warm season results in a growth of the yearly mean of the NH₃ emission of 4.3% (

Table 1. Descriptive statistics (maximum, 3rd quartile, median, mean, 1st quartile and minimum) of the relative modification of the NH₃ emission MOD (%) between the reference building REF and the application of the seven AMs (stocking density SD80%, stocking density SD60%, inversion of the resting and activity periods INV, doubling the ventilation rate VENT, cooling pads CP, cooling pads and heat exchanger CPHE, and earth-air heat exchanger EAHE). A reduction of the ammonia release is highlighted in bold.

	Relative Ammonia Difference (%)
	SD80%	SD60%	INV	VENT	CP	CPHE	EAHE
Maximum	5.0	6.9	4.3	17.6	6.0	5.8	13.0
3rd Quartile	0.6	0.4	−1.1	8.1	0.4	0.2	5.1
Median	−0.7	−0.9	−2.7	3.1	−1.4	−1.3	−3.2
Mean	−0.7	−1.7	−2.6	4.3	−2.0	−1.7	−3.1
1st Quartile	−2.1	−3.9	−4.2	0.1	−4.0	−3.4	−11.4
Minimum	−7.1	−9.9	−7.7	−4.9	−11.1	−10.0	−19.0

).

The EAHE causes a higher indoor air temperature (Figure 2, EAHE) and a higher ventilation rate during the cold season (Figure 3, EAHE). This results in a higher NH₃ emission during the cold season as well. This increase is compensated by the efficacy of the cooling during summertime. The EAHE shows the highest NH₃ reduction of all AMs by a mean value over the year of −3.1% (Table 1).

All AMs except VENT reduce the mean NH₃ emission between −0.7% (SD80%) and −3.1% (EAHE).

4. Discussion

The release of NH₃ by a surface inside livestock buildings can be described by models, which use a gradient between the surface and air concentration and a convective mass transfer coefficient [54]. The parameterisation of this coefficient for livestock buildings is performed for nearly all approaches by air temperature and air velocity (e.g., dairy [40], layers [55], pigs [56], and manure [43,57,58]). For the NH₃ emission due to the storage and spreading of manure, and also the dry matter content, pH, and the proportion of N/NH_4, are relevant predictors [59]. These parameters can only be included in a parameterisation on farm level. The NH₃ release inside the livestock building depends on the air temperature, the air velocity close to the release surface, and the activity of the animals e.g., [40,43,44,60,61,62]. These parameters are related to meteorological parameters, depending on the ventilation system (mechanically or naturally ventilated), the stocking rate, and the thermal properties of the building [47,48,49]. Gyldenkærne et al. [42] calculated the release modification factor for livestock buildings (about 34% of the NH₃ emissions) by a power function, with an exponent b by R~T_iv_i^b with the indoor air temperature T_i and the air velocity v_i close to the surface where NH₃ is released. These two parameters can be calculated by a simple parameterisation [63] or by more sophisticated simulation models [28,46]. Besides the indoor air temperature and air velocity, the animal activity should be considered as a predictor for the diurnal variation of the release modification factor. The temporal trend of the NH₃ emission due to global warming shows a relative increase of 0.16% per year. However, following the clean air endeavour between 1990 and 2015, emissions over that period were reduced by 23% in Europe. The global warming signal is counteracting this reduction in the range of 4% during this period, which means that the overall decrease for ammonia emission was only 19%. For Austria, with a global warming increase of 1% from 1990 to 2015, this gives an increase in emissions of 5% instead [28].

Due to the commitment of the EU regulation to reduce NH₃ emissions until 2030, several abatement techniques are under discussion. Besides the storage of manure and its application on fields, the emission of the livestock building causes about 2/3 of the NH₃ emission of pigs. Many techniques show a wide range of reduction factors and corresponding costs [23,64,65,66,67,68,69,70,71]. Most of these reduction techniques propose a restriction of the size of the NH₃ release surface on animal level (e.g., living zone, dunging area) and for manure storage, permanent cleaning of the animal area, and cooling of the manure. To reduce the emission in the outlet air from mechanically ventilated livestock buildings, end-of-pipe systems are also in use. Acid scrubbers can achieve an emission reduction close to 100% and bio-scrubbers have an average ammonia removal of 70% [72,73,74]. The outlet air purification is limited to mechanically ventilated buildings, with the highest costs compared to other mitigation measures, showing declining costs with growing livestock [23,75].

Due to global warming, AMs are applied to alleviate heat stress inside livestock buildings. These AMs can be grouped into measures including energy-saving air treatment systems, which cool the inlet air (e.g., cooling pads, earth-air heat exchanger), the use of certain building elements (e.g., insulation), optimising building characteristics (e.g., spatial orientation), the modification of the indoor climate at the animal level (e.g., fogging, cooling the drinking water, increasing air velocity), and the adaptation of livestock management (e.g., the reduction of stocking density) [53]. Due to the fact that indoor air temperature is a major predictor for NH₃ emission, some of these AMs can be assumed as feasible to mitigate NH₃ emission. In this study, only those AMs were investigated, which can be handled by a simulation model of the indoor climate of a livestock building [52]. It turned out that those AMs that cool the inlet air (especially CP and CPHE) not only decrease the indoor air temperature best (Figure 2) and do not change the ventilation rate much (Figure 3), but they also reduce the NH₃ emission to quite an extent (Figure 5). The EAHE, in contrast, causes a higher indoor air temperature (Figure 2, EAHE) and a higher ventilation rate during the cold season (Figure 3, EAHE). This results in a higher NH₃ emission during the cold season as well. This increase is, however, compensated by the efficacy of the cooling during summertime. The EAHE shows the highest NH₃ reduction of all AMs by a mean value over the year of −3.1% (Table 1). INV is second in reducing the NH₃ emission (−2.6%, Table 1) but shows a comparatively low reduction of summertime indoor air temperatures (Figure 2) and an increase in summertime ventilation rates (Figure 3). SD60% and SD80% are less effective in reducing the NH₃ emission. VENT is different from all other AMs in that it shows an increase of the air velocity close to the release surface of NH₃ during the summer months, causing a yearly mean increase of the NH₃ emission of 4.3% (Table 1).

Besides such simulation models, empirical studies were performed. Pertagnol [76] investigated cooling pads, high-pressure fogging systems, and a modified earth-air heat exchanger, and found a reduction of the NH₃ emission of 29%, 28%, and 20%, respectively. These reductions were calculated only for those days with an outdoor air temperature above 22 °C. For the entire year, the decline of the NH₃ emission is in general lower by 24%, 31%, and 14%. Jeppsson et al. [77] found a NH₃ reduction between 29% and 49% for showers for fattening pigs. The following reasons were discussed for this reduction: (1) reduced indoor air temperature; (2) a scrubber effect by wet surfaces; and (3) reduced pen fouling and partly a dilution of urine on the slatted area and on the surface of the slurry. The last two aspects are not included in the simulation model of this study. The empirical investigations show a higher reduction compared to the simulated values. The AM, which uses a doubling of the ventilation rate, causes an increase of NH₃ emission in the mean. Other AMs which use additional fans to increase the air velocity close to the animals (forced ventilated livestock buildings, e.g., boost, circulation fans, or hybrid ventilation systems) will cause a similar effect.

The detected reduction of NH₃ emissions by cooling systems should be considered in the decision process. In this respect, all systems, which increase the air velocity inside livestock buildings, should be avoided (e.g., additional fans). This study is a valuable example that not only the isolated effect of animal health and animal welfare should be considered, but also aspects of environmental protection and the related human health as part of the “One Health” concept [78,79].

5. Conclusions

Due to global warming, the application of AMs to alleviate HS inside livestock buildings is becoming more and more common. We postulated that the AMs selected for this study will also contribute to a reduction of NH₃ emissions. To determine the NH₃ release, the modification by the indoor climate (temperature, ventilation rate, and the animal activity by the time of the day) was taken into account. Monthly mean values of the NH₃ release for the reference case REF, a representative livestock building for fattening pigs (body mass between 30 and 120 kg, mechanically ventilated) for central Europe for 1800 heads, were calculated and compared to the values obtained by seven selected AMs. The time period spans the years 1981 to 2017. The results reveal quite an ambiguous picture; for all AMs investigated, both an increase and a decrease in NH₃ emissions compared to REF were found, although on average, a decrease between −0.7 and −3.1% was calculated. For those adaptation measures which cool the inlet air, the highest NH₃ reduction was found with −3.1% for EAHE, −1.3% for CPHE, and −1.4% for CP.

The only exception is VENT, which shows an increase of 4.3%. This is caused by the increased air velocity inside livestock buildings, and thus all AMs applying this feature should be avoided.

So, in principle, the postulation is fulfilled, i.e., an alleviation in HS inside livestock buildings is accompanied by a reduction of NH₃. AMs that cool the inside air (CP, CPHE, EAHE) are to be preferred over those reducing the stocking density (SD80%, SD60%) or increasing the ventilation rate (VENT). An inversion of the feeding and resting times by half a day to move the maximum heat release of the animals to night-time (INV) is comparably successful as CP or CPHE. In practice, the costs will also determine which AM is going to be applied to improve the well-being of the animals.