Atmospheric new aerosol particle formation observed in remote areas (e.g., in Finland, Portugal and in the U.S.). is generally attributed to low-volatile oxidation products of monoterpenes (C10H16), which are emitted by the vegetation. In this article we show that this atmospheric new particle formation is not caused by monoterpene products, but most likely initiated by very low-volatile substances produced during sesquiterpene (C15H24)-ozone reactions. For this purpose, the nucleation times of the most abundant monoterpene reactions have been calculated and discussed exemplarily for the Finnish site Hyyti¿l¿, at which nucleation events have been observed. In addition, the important negative influence of water vapor on the nucleation threshold of the ¿-caryophyllene-ozone reaction has been studied in detail at different dew points in the laboratory. Therein, the saturation vapor pressure of the nucleating compounds was estimated to be less than 1.2 ¿ 10-10 hPa, which is recommended for atmospheric homogeneous nucleation of non-volatile organics.