## 1 Introduction  
Air pollution has far-reaching environmental consequences, including the acidification of rivers, soils, and the atmosphere, the eutrophication of lakes and rivers, ozone layer depletion, and intensified greenhouse effects [1, 2, 3, 4]. Various VOCs are responsible for these nuisances, such as chlorobenzene (CB) and chloronaphthalene (CN), which are chemicals from the cement industry [5, 6, 7]. The impact of CB and CN extends beyond environmental concerns, as these chemicals pose toxicity risks to human health [6]. Notably, due to their volatility, cement workers face potential exposure to these VOCs, presenting a significant public health challenge [8; 9; 10; 11].  
In response to these challenges, since the 1980s regulations have been established to limit the emissions of these compounds into the air, safeguarding worker health. For the good application of these rules, it is, thus, necessary to continue to propose to industrialists innovative treatment solutions adapted to these gas emissions. Consequently, research advancements in photocatalysis have revealed the efficacy of this chemical process for purifying air contaminated by VOCs through continuous reactors.  
Heterogeneous photocatalysis involves the absorption of photons by a semiconductor with an energy equal to or greater than that of the band gap (\(\mathrm{E_{c}-E_{v}}\)), facilitating the flow of electrons from the valence band (\(\mathrm{E_{v}}\)) to the conduction band (\(\mathrm{E_{c}}\)) [12; 13]. This process generates a positive hole (h+) at the valence band and releases an electron (e\(-\)) into the conduction band [14; 15]. This chemical process consists of oxidizing the pollutant on a catalyst (TiO\({}_{2}\) usually) under UV radiation [16; 17; 18]. In the presence of oxygen and/or water vapor, the UV radiation that activates the semiconductor (catalyst) allows for the VOCs in contact with the reactive surface to convert into CO\({}_{2}\) and H\({}_{2}\)O [19; 20; 21].  
Photocatalysis generally proceeds in three steps: the mass transfer of the pollutant to the catalyst, the adsorption on the catalyst, and the chemical reaction. Among continuous photocatalytic reactors, tangential flow configurations, which consider the VOC concentration, UV intensity, and water vapor composition, offer adaptability to an industrial scale [22]. The desorption and diffusion processes of VOCs and their by-products are typically negligible, and steady-state kinetic models often overlook the mass transfer effects. Thus, the adsorption of the pollutant and the oxidation reaction are usually described by the Langmuir-Hinshelwood (L-H) theory [23; 24; 25; 26]. In this study, a continuous-tangential-flow bioreactor is employed to assess the impact of the mass transfer on the degradation of CB and CN at industrial concentrations. The investigation includes an analysis of the influence of the flow rate, concentration, and relative humidity (RH) of the air stream on the degradation rate. Additionally, a Langmuir-Hinshelwood (L-H) modeling of the experimental results is conducted.  
The scientific challenge addressed in this work is to highlight the effect of chlorinated radicals on the performance of photocatalytic reactors. In fact, the novelty is based on the treatment of simulated gas air from a cement factory. The experiments were carried out on a pilot scale under conditions similar to those on site. This was done in favor of emphasizing the true photocatalytic performances. A modeling component was established to underscore the effect of the mass transfer on the removal kinetics. To the best of our knowledge, there is no existing work on these pollutants at a pilot scale.