A 41-year-old actor, Eddie Connor, who has lived in London all his life and who suffers from a severe form of asthma, recognizes the signs all too well.
"I start coughing or I feel my breathing getting shallower. It's like putting a piece of cling-film over my face," said Connor, who blames air pollution and particularly diesel fumes in the British capital for triggering his symptoms.
Pockets of central London rank among the most polluted in Europe and the city's emissions exceed European Union norms, although on average it ranks relatively well compared to other EU capitals such as Amsterdam and Paris.
Up to 9,416 people are estimated to have died in London as a result of long-term exposure to pollution in 2010, according to a study by King's College London (KCL) published in July, a fifth of all deaths that year.
The research showed for the first time the health impacts of two pollutants found in exhaust fumes from diesel vehicles -- nitrogen dioxide (NO2) and fine particulate matter (or PM2.5) -- and showed that the problem was far greater than previously thought.
"You could take very dramatic steps immediately," said, James Thornton, a former environmental lawyer and chief executive of ClientEarth, which brought and won a case against the UK government this year over failure to comply with EU limits.
"This is not rocket science -- you need to have Ultra Low Emission Zones, you need to ban the worst diesels, you need to take steps on traffic management."
Billions in costs
Diesels now account for a majority of UK new car sales, a result of their reputation for being cheaper and more environmentally-friendly than petrol alternatives along with years of favorable government policy aimed at cutting carbon emissions.
But recent evidence shows that the particulates in diesel emissions can cause a variety of health problems due to their ability to penetrate deep into the lungs and cross into the bloodstream.
The cost to London's economy of these health impacts ranges up to Ģ3.7 billion (5.0 billion euros, $5.7 billion) yearly, the KCL study showed.
According to World Bank data, London ranked 2,516th out of 3,226 world cities with a population of more than 100,000 in a ranking that put the most polluted cities at the top.
Amsterdam and Paris scored slightly worse than London, although parts of the city centre such as Oxford Street -- often clogged with buses and taxis -- have recorded alarmingly high spikes in pollutants that are among the highest in Europe.
Gary Fuller, an air pollution scientist at KCL, said the problem of inadequate vehicle emissions testing exposed by the recent Volkswagen cheating scandal may be a factor in the high levels of NO2 in London.
"For a long time now -- we've been pointing this out since 2003 -- air pollution in London hasn't been going down as fast as it should be," said Fuller.
'Jump in awareness'
A draft government air quality plan last month admitted that the combined impact of NO2 and particulates "represents a significant public health challenge" but said EU limits for NO2 in London would not be reached until 2025 at the earliest.
It blamed the "the size and complexity" of the capital's transport networks and suggested the introduction of more electric cars and the use of more low-emission technologies as the way forward.
The proposals follow a ruling by Britain's Supreme Court in April which declared NO2 levels in the UK illegal and ordered the government to act.
London's City Hall says that the mayor's plans to tackle air pollution "will ensure that 80 percent of central London meets EU legal limits for NO2 by 2020".
But some people cannot wait that long.
Former British science minister Paul Drayson, who himself suffers from asthma, last month launched a pollution monitoring app called CleanSpace designed to create a crowd-sourced network which will allow users to plan cleaner routes of travel.
Drayson said he hoped the technology would lead to "a major jump in awareness and action on air quality".
"People lack access to useful, actionable information about the air quality where they are and what they can do to reduce their exposure," he said.