noun
feeling of loneliness; feeling of desolation
A somewhat literary or introspective term for a deep sense of loneliness or desolation, often associated with quiet, empty, or melancholic atmospheres.
夕暮れの公園に一人でいると、寂寥感に襲われる。
When I am alone in the park at dusk, a feeling of desolation washes over me.
彼の絵には、都会の寂寥感がよく表れている。
His paintings often capture the loneliness of the city.
寂しさ is the general, neutral noun for 'loneliness' or 'sadness', whereas 寂寥感 is a heavier, more poetic term for a profound sense of desolation.
Compound of 寂寥 (せきりょう, 'loneliness, desolation') and 感 (かん, 'feeling, sense'). 寂寥 is a Sino-Japanese word (kango) using kanji that convey stillness and emptiness.