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The environment of S187, a nearby H II region (1.4$\pm$0.3 kpc), is analyzed.A surrounding shell has been studied in the H I line, molecular lines, and alsoin infrared and radio continua. We report the first evidence of a clumpy HIenvironment in its photodissociation region. A background radio galaxy enablesthe estimation of the properties of cold atomic gas. The estimated atomic massfraction of the shell is $\sim$260~M$_{\odot}$, the median spin temperature is$\sim$50~K, the shell size is $\sim$4 pc with typical wall width around 0.2 pc.The atomic shell consists of $\sim$100 fragments. The fragment sizes correlatewith mass with a power-law index of 2.39-2.50. The S187 shell has a complexkinematical structure, including the expanding quasi spherical layer, molecularenvelope, an atomic sub-bubble inside the shell and two dense cores (S187~SEand S187~NE) at different stages of evolution. The atomic sub-bubble inside theshell is young, contains a Class II young stellar object and OH maser in thecentre and the associated YSOs in the walls of the bubble. S187~SE and S187~NEhave similar masses ($\sim$1200~M$_\odot$ and $\sim$900~M$_\odot$,respectively). S187~SE is embedded into the atomic shell and has a number ofassociated objects including high mass protostars, outflows, maser sources andother indicators of ongoing star formation. No YSOs inside S187~NE weredetected, but indications of compression and heating by the H II region exist.

Fragmented atomic shell around S187 HII region and its interaction with molecular and ionized gas