notoriously
adv.used to describe something that is famous for being bad or difficult. You use it when everyone knows about a negative quality.
adv.used to emphasise that a quality or fact, typically a negative one, is widely known or famous.
“The weather in this city is notoriously unpredictable.”
“The local government is notoriously slow at processing new building permits, often taking months to respond.”
“While the author's prose is celebrated for its beauty, his personal life was notoriously chaotic, marked by frequent public arguments and financial instability.”
Typically placed before the adjective it modifies to highlight a well-known negative trait.
Usage notoriously difficult
“These sources are called Galactic PeVatrons, and they are notoriously hard to pin down.”
“Researchers have found a clever new way to map a part of Earth’s upper atmosphere that is notoriously difficult to observe.”
Common in science writing
From Middle English notoryously, equivalent to notorious + -ly.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.