Formation of cluster mode particles (1-3 nm) in preschools.

This study is the first study that reports the cluster particle (1-3 nm) formation (CPF) in two modern preschools located in Nur-Sultan city of Kazakhstan from October 28 to November 27, 2019. The average particle number concentration and mode diameter values during major CPF events in Preschool I and Preschool II were found to be 1.90 × 10 (SD 6.43 × 10) particles/cm and 1.60 (SD 0.85) nm, and 1.11 × 10 (SD 5.46 × 10) particles/cm and 2.16 (SD 1.47) nm, respectively. The ultraviolet PM concentration reached as high as 7 μg/m in one of the measurement days. The estimated emission rate in Preschool I for CPF events was 9.57 × 10 (SD 1.92 × 10) particles/min. For Preschool II, the emission rate was 7.25 × 10 (SD 12.4 × 10) particles/min. We identified primary cluster particles (CPs) emitted directly from the sources such as candle burning, and secondary CPs formed as a result of the oxidation of indoor VOCs or smoking VOCs. The secondary CPs are likely to be SOA. Indoor VOCs were mainly emitted during cleaning activities as well as during painting and gluing. Indoor VOCs are the controlling factors in the CPF events. Changes in the training and cleaning programs may result in significant reductions in the exposure of the children to CPs.