###### Abstract  
Adverse health effects caused by exposure to airborne particles have been detected in recent years, however there is little knowledge about exposure to ultrafine particles with a diameter <100 nm. In this study, particle number concentration and size distribution in a range of particle diameters from 10 nm to 10 \(\upmu\)m were determined during oak wood sanding. A hand-held orbit sander in combination with three types of grit size (P60, 120 and 240) of sandpaper were used. Measurements were obtained using a portable particle size distribution analyzer and an optical particle size spectrometer, carried out at 15-min intervals for each treatment by static sampling in the breathing zone. We also compared the optical particle size spectrometer to the aerosol monitor in order to evaluate the mass concentration of airborne particles in the range of 1 to 10 \(\upmu\)m in diameter. Sanding paper with the finest grit, P240, showed a significantly higher number concentration of ultrafine particles, compared with P60 and P120 grits. The differences among particular grit size were statistically significant for microparticles. The size distribution of particles during sanding was not affected by grit size. For each grit size, apparent peak values of ultrafine and microparticle number concentrations were determined at approximately 15 nm, and 0.1 \(\upmu\)m, respectively. Optical particle size spectrometer and aerosol monitor showed comparable results of mass concentration for the respirable fraction. g 2022127644 202212764 202  
the lung deposition of particles and the potential for the surface chemistry is to use a metric called the lung deposited surface area (LDSA) concentration. The LDSA concentration is considered a relevant metric for the negative health effects of aerosol particles, which can be measured by real-time measuring instruments [6]. According to [PERSON] et al. [7], various researchers use different metrics and find them informative, therefore, comparing results across multiple studies is difficult given the lack of consistency in the metrics used. Sanding oak wood with hand-held power tools within woodworking shops has been associated with high inhalable wood dust exposure [8; 9; 10]. Oak wood dust is considered to be carcinogenic to humans, according to the International Agency for Research on Cancer [11]. The size and shape of particles are primordial factors that condition their deposition in the airways. The largest particles (10-20 \(\upmu\)m) are deposited onto the walls of the nose and pharynx, while particles of \(<\)5 \(\upmu\)m size usually impact smaller airways such as bronchial districts and alveoli [12]. For comparison, the range of droplet sizes of an average human when talking and coughing varies between 25 and 50 \(\upmu\)m, and 4 and 7 \(\upmu\)m, respectively [13; 14]. The size of typical aerosols from air conditioners, and technical systems for humidification and spraying, range from 0.3 to 10 \(\upmu\)m [15; 16]. Occupational exposure limits for oak wood dust have been established in many countries. In Europe, a binding 8-hr time weighted average (TWA) limit value of 2 mg/m\({}^{3}\) (3 mg/m\({}^{3}\) until 17 January 2023) was set by European Union Directive 2017/2398 [17]. A number of studies have investigated the effect of various factors on airborne particle size distribution and mass concentration during the sanding of wood. [PERSON] and [PERSON] [18] investigated the effect of wood density, sandpaper grade, and contact pressure, on the production of dust. Results from their study indicated that in the case of hardwoods, there is a tendency for the mean aerodynamic diameter of the wood particles generated to be larger for the coarser grades of sandpaper. In addition, fine and coarse sandpaper produced similar concentrations of airborne dust. [PERSON] et al. [19] reported that the geometric mean particle size of the dust produced during the sanding process was significantly influenced by wood density and hardness.