What Is A London Particular?
From Brewer’s Britain and Ireland:
London Particular. A Colloquial term used in the 19th and early 20th centuries for a London fog. The sulphurous coal smoke of the period gave London smogs a yellowish tinge (whence the name pea-souper, after soup made from yellow split peas rather than fresh green peas), and it may be that the term was inherited from a variety of Madeira wine of similar colour, so called because it was imported ‘particularly’ for London merchants.
“This is a London particular.’ I had never heard of such a term. ’A fog, miss’, said the young gentleman.”
Charles Dickens: Bleak House (1852)