Quality control of atmospheric air is a priority topic for monitoring the environment. There is a great need for rapid and cost-effective control of atmospheric pollution. The protected and park zones play a recreational role, therefore the assessment of air quality in this area is especially important. For the first time active biomonitoring (moss bags technique) was applied in Moscow, at the state museum-reserve Tsaritsyno. As a bioindicator the moss Sphagnum girgensohnii was chosen. This species was collected in a pristine wetland area Domkino Bay, near Dubna, Russia. S. girgensohnii was bagged and exhibited at three locations of Tsaritsyno from June to September of 2017. The goal of this pilot study was to assess air pollution with trace elements from potential pollution sources in Moscow. A total of 32 chemical elements: Na, Mg, Al, Cl, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Zn, Se, As, Br, Rb, Mo, Sr, Sb, Ba, Cs, La, Sm, Tb, Ce, Hf, Ta, W, Th, and U were determined in the exposed samples by neutron activation analysis at the reactor IBR-2 of FLNP, JINR, and three environmentally meaningful elements: Pb, Cu, and Cd were determined by atomic absorption spectrometry in the same laboratory. Obtained results showed increase of the concentration of elements considered as environmental pollutants, Sb, Cr, V, etc., in moss samples exposed at different sites in Tsaritsyno park, which requires attention from the Moscow authorities. Sphagnum girgensohnii proved to be a cheap and efficient tool to assess heavy metal pollution in urban area.