Research PaperAssessing particulate matter (PM10) emissions from outdoor runs in laying hen houses by integrating wind tunnel and lab-scale measurements
Introduction
High environmental concentrations of particulate matter (PM) are regarded as a cause of concern for human health (Pope, 2007). Livestock activities are long known to play an important role in PM concentration raises both in indoor and outdoor environments (Cambra-López, Aarnink, Zhao, Calvet, & Torres, 2010; EEA, 2016). In fact, both the coarser (PM10; particles with an aerodynamic diameter <10 μm) and finer (PM2.5; particles with an aerodynamic diameter <2.5 μm) fractions of PM are held responsible for negative health effects in farmers and local residents surrounding livestock houses. Furthermore, high dust concentrations affect indoor air quality and health and welfare of animals (Borlée et al., 2017; Cambra-López et al., 2010). Several studies have addressed the issue of PM emissions from poultry houses, quantifying the emission fluxes (Hayes, Curran, & Dodd, 2006; Roumeliotis & Van Heyst, 2008; Yao et al., 2018) and proposing mitigation measures (Cambra-López, Winkel, Harn, Ogink, & Aarnink, 2009; Melse, Hofschreuder, & Ogink, 2012; Winkel et al., 2016). Most of these studies focused on emissions coming from poultry houses, while very little information is available on the contribution of the outdoor runs on the overall emissions. Nonetheless, in Europe, free range rearing systems, which give poultry access to large outdoor runs, are becoming more common due to their positive effects on poultry and hens welfare and wellbeing (Coton et al., 2019; Moyle et al., 2014). In particular, according to EU regulation requirements (Commission Delegated Regulation (EU) 2017/2168), free range laying hens rearing is characterised by continuous daytime access to outdoor runs, with 4 m2 hen−1 of open space. Due to the increasing development of these production systems, it is necessary to investigate the magnitude of emissions deriving from outdoor areas. Assessing emissions from area sources in open space environments presents some difficulties, especially in case the sources are not homogeneous (Dumortier, Aubinet, Lebeau, Naiken, & Heinesch, 2019). The main methodologies that have been used to address this kind of sources in similar applications, such as cattle feedlots, are micrometeorological techniques and wind tunnel methods (Misselbrook, Nicholson, Chambers, & Johnson, 2005). Micrometeorological techniques such as the integrated flux method (Denmead, 1983) and dispersion models (Bonifacio et al., 2012; Flesch, Wilson, Harper, Crenna, & Sharpe, 2004) have proven to be very effective in back calculating emission fluxes from open field emission sources. These systems, however, despite their large range of application, have the common disadvantage of being unsuited to estimate emissions from sources, such as the outdoor runs, which are in proximity of multiple other sources of the same pollutant (e.g. barn, manure storage facilities etc.), due to cross interference. Wind tunnels are enclosure systems which have been widely used to assess PM and gaseous emissions from soil or other ground level area sources (Dinuccio, Gioelli, Balsari, & Dorno, 2012; Gao et al., 2020; Kabelitz et al., 2020) and allow to monitor the emissions, gathering data under standardised wind speed conditions. Aarnink, Hol, and Beurskens (2006) used a ventilated chamber technique to assess ammonia (NH3) emissions from outdoor runs in laying hen houses, but did not address PM emissions. The main constraint regarding the use of a classical wind tunnel method to assess emissions from outdoor runs is linked with the hens behavior. In fact, hens often engage in dust bathing behavior, which was recognised as a form of personal hygiene and also as a social behavior which has beneficial effects on animal welfare (Abrahamsson, Tauson, & Appleby, 1996; van Liere, Kooijman, & Wiepkema, 1990; Vestergaard, Skadhauge, & Lawson, 1997). When hens dustbathe in outdoor runs soil, they can cause soil (re)suspension in the air leading to PM emissions. Therefore, in order for a wind tunnel to effectively assess outdoor runs PM emissions, it should allow to assess the emission deriving from dustbathing and other hen activities.
The main aim of this work is to develop a multi-step methodology to assess outdoor runs emissions of PM and identify the role of hens behavior and soil moisture as main drivers of the emission. A wind tunnel prototype was designed to allow the hens to enter it willingly and dustbathe inside of it, in order to assess the effect of hen density (HD, hens m−2) on the emissions. Moreover, the emission potential of the outdoor run soil was assessed, using a Soil Resuspension Chamber (SRC) method to assess the effect of soil humidity on PM release. The gathered information, combined with daily meteorological data and evapotranspiration (ET) modelling, was utilised to assess PM emissions over a 1-year period.
The gathered results will allow to acquire a better understanding of poultry generated PM emissions by addressing some of the main factors driving PM formation from free range areas in poultry houses. Moreover, it will provide a new perspective on hens behavior, addressing its influence on PM emissions.
Section snippets
Wind tunnel design
Wind tunnels used for PM and gaseous emission assessments have a wide variety of shapes, but they usually share some common elements. They are built in sturdy material, such as plastic or stainless steel, they have a main chamber, which has the purpose of enclosing the studied area source, and they are provided with input and output pipes. The wind speed inside the tunnel (WStunnel, m s−1) is generated using a ventilator and normally set to a value that matches the average outdoor wind speed (
Wind tunnel flow and wind speed charts
The first flow rate tested was of 0.95 ± 0.01 m−3 s−1, leading to a wind speed of 1.8 ± 0.03 m s−1, which matches the expected wind speed of the area (ExpWS(0.2 m) = 1.8 m s−1). Since the hens were reluctant to enter the tunnel at this high wind speed, a lower flow rate of 0.73 ± 0.01 m−3 s−1 was used, leading to an average wind speed inside the tunnel of 1.5 ± 0.11 m s−1. The average wind speed inside the tunnel was measured at 12 positions, at 0.20 m height, and resulted in higher values in
Wind tunnel validation: internal wind speed and capture efficiency
The results showed a slightly uneven distribution of the wind speed inside the tunnel. This is due to the friction effect of the tunnel walls and to the turbulence created by the funnel structure leading to the outlet pipe. The variations observed are consistent with those observed by Balsari et al. (2006), who adopted a similar wind tunnel design. The average wind speed inside the tunnel, of approx. 1.5 m s−1, is only slightly lower than the expected WS at that height (1.8 m s−1), calculated
Conclusions
A wind tunnel method to assess the effect of hen density on PM emission from outdoor runs in free range laying hens houses was successfully developed. The methodology allowed to measure PM emissions levels from hens activity and to study the influence of hens behavior on the emissions. HD influences PM10 emissions, causing them to increase exponentially when a higher number of animals are present per surface area unit (ER = e (0.94 HD+2.14)). The emission fluxes deriving from the outdoor runs
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Funding: This study has been funded by the Ministry of Infrastructure and Water Management of the Netherlands.
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