Editing London congestion charge (section)

=== Air quality ===
The pre-commencement report from TfL noted that the scheme was not expected to significantly affect [[air quality]], but that offering a discount to encourage the use of greener fuels would be a positive measure.<ref name="tflprereport" />

TfL reported that levels of [[nitrogen oxides]] (NO<sub>X</sub>), fell by 13.4% between 2002 and 2003, and carbon dioxide, as well as the levels of [[Atmospheric particulate matter|airborne particulates]] (PM10) within and alongside the [[Inner Ring Road, London|Inner Ring Road]] boundary of the zone.<ref name="tfljune2006" />

Since 2002, the [[nitrogen dioxide]] (NO<sub>2</sub>) produced by [[diesel exhaust]] has become a serious problem, with the [[London Air Quality Network]] of [[Imperial College]] reporting that the annual mean NO<sub>2</sub> objective (of 40 μgm-3 or 21 ppb) was exceeded at all kerbside and roadside monitoring sites across central and greater London during 12 months between 2005 and 2006.  Although no areas within the Congestion Charge Zone reported NO<sub>2</sub> levels above an upper limit of 200 μgm-3 (105 ppb), some monitoring areas near the zone boundary experienced very long periods at such levels, notably the [[A23 road|A23]] near Brixton (3741 hours) and the [[Marylebone Road]] (849 hours).<ref name=laqn>{{cite web |url=http://www.londonair.org.uk/london/reports/AirQualityInLondon2005andmid2006.pdf |title=Air Quality in London 2005 and mid 2006 – Briefing |last=Fuller & Green |date=28 July 2006 |publisher=London Air Quality Network |access-date=8 January 2008}}</ref>

In 2007, the ''Fifth Annual Monitoring Report'' by TfL stated that between 2003 and 2006, NO<sub>X</sub> emissions fell by 17%, PM10 by 24% and CO<sub>2</sub> by 3%, with some being attributed to the effects of reduced levels of traffic flowing better, with the majority being as a result of improved vehicle technology.<ref name="tfljune2007" /><ref name="glareport">{{cite web |url=http://www.airquality.co.uk/archive/reports/cat09/0505171128_London_Congestion_Charge_Detailed_Assessment.doc |first=Lucy |last=Sadler |title=Detailed assessment London congestion charging |format=DOC |access-date=20 January 2008 |publisher=UK Air Quality Archive|archive-url = https://web.archive.org/web/20080228180759/http://www.airquality.co.uk/archive/reports/cat09/0505171128_London_Congestion_Charge_Detailed_Assessment.doc |archive-date = 28 February 2008}}</ref> In total, the rate of fall in CO<sub>2</sub> has been almost 20% as of 2007.<ref>{{cite news |title=Milan introduces traffic charge |url=http://news.bbc.co.uk/1/hi/world/europe/7167992.stm |work=BBC News |date=2 January 2008 |access-date=20 January 2008 |archive-url=https://web.archive.org/web/20150429041527/http://news.bbc.co.uk/2/hi/europe/7167992.stm |archive-date=29 April 2015 |url-status=live}}</ref>

The 2007 TfL report makes it clear that only a one-off reduction of emissions could be expected from the introduction of the charge, whilst further reductions are unlikely to be as a result of the charge.  It notes that lower vehicles emissions may not necessarily feed through into improvements in air quality as vehicle emissions are only one contributor to total emissions of a particular pollutant along industrial sources and that weather conditions play a significant role, and that pollutant concentrations were being affected by changes in the make up of the vehicle fleet.  It also suggests that the rate of decline in certain pollutants is decreasing.<ref name="tfljune2007" />

A 2011 independent study published by the [[Health Effects Institute]] (HEI), and led by a researcher from [[King's College London]], found that there is little evidence the congestion charge scheme has improved air quality.  This research used modelling and also compared actual air pollutant measurements within the congestion charge zone with those of control sites located in Outer London.  The investigators concluded that "it is difficult to identify significant air quality improvements from a specific program{{snd}}especially one targeted at a small area within a large city{{snd}}against the backdrop of broader regional pollutant and weather changes."<ref>{{cite web|url=http://www.greencarcongress.com/2011/04/hei-study-finds-london-congestion-charging-scheme-shows-little-evidence-of-improving-air-quality.html#tp |title=HEI study finds London Congestion Charging Scheme shows little evidence of improving air quality|publisher=[[Green Car Congress]]|date=27 April 2011|access-date=22 May 2011}}</ref>  National trends had already shown a rapid decline of some other emissions during the late 1990s, notably [[carbon monoxide]], and levels have been relatively stable since 2002 across London.{{citation needed|date=April 2012}}

A 2020 study of London found that the London congestion charge led to reductions in pollution and reductions in driving, but it increased pollution from diesel taxis and buses (which are exempt from the charge).<ref>{{Cite journal|last1=Green|first1=Colin P.|last2=Heywood|first2=John S.|last3=Navarro Paniagua|first3=Maria|date=2020-09-01|title=Did the London congestion charge reduce pollution?|url=http://www.lancaster.ac.uk/media/lancaster-university/content-assets/documents/lums/economics/working-papers/LancasterWP2018_007.pdf|journal=Regional Science and Urban Economics|language=en|volume=84|pages=103573|doi=10.1016/j.regsciurbeco.2020.103573|bibcode=2020RSUE...84j3573G |s2cid=169274952|issn=0166-0462}}</ref>

{| class="wikitable"
|-
|
| colspan="3" | Charging zone
| colspan="3" | Inner Ring Road
|-
|
| NO<sub>X</sub>
| PM10
| CO<sub>2</sub>
| NO<sub>X</sub>
| PM10
| CO<sub>2</sub>
|-
| Overall traffic emissions change 2003 versus 2002<ref name="tfljune2006" />
| −13.4
| −15.5
| −16.4
| −6.9
| −6.8
| −5.4
|-
| Overall traffic emissions change 2004 versus 2003<ref name="tfljune2006" />
| −5.2
| −6.9
| −0.9
| −5.6
| −6.3
| −0.8
|-
| Changes due to improved vehicle technology 2003-2006<ref name="tfljune2007" />
| −17.3
| −23.8
| −3.4
| −17.5
| −20.9
| −2.4
|-
| colspan="7" style="text-align:center;font-size:90%;"|<small>Source: {{cite web |url=http://www.tfl.gov.uk/cdn/static/cms/documents/FourthAnnualReportFinal.pdf |title=Impacts Monitoring – Fourth Annual Report |publisher= [[Transport for London]] |archive-url=https://web.archive.org/web/20150429042848/http://www.tfl.gov.uk/cdn/static/cms/documents/FourthAnnualReportFinal.pdf |archive-date=29 April 2015 |url-status=live}} and {{cite web |url=http://www.tfl.gov.uk/assets/downloads/fifth-annual-impacts-monitoring-report-2007-07-07.pdf |access-date=23 November 2007 |date=June 2007 |title=Impacts Monitoring – Fifth Annual Report |archive-url=https://web.archive.org/web/20140122090211/http://www.tfl.gov.uk/assets/downloads/fifth-annual-impacts-monitoring-report-2007-07-07.pdf |archive-date=22 January 2014 |publisher=[[Transport for London]] |url-status=live}} 2003–2004 figures are TfL estimates. </small>
|}