Changed sources identified within Brighton & Hove since 2019
Around Valley Gardens II A23 traffic flow has been altered to include two-way general traffic on the east side and buses on the westside. Additional Georeferenced buses (about one fifth of the bus fleet) will alter what emissions in the ULEZ and other parts of the AQMAs.
These updates can be woven into the emission and dispersion model assessments prior to the AQAP going to committee.
Additional air quality works undertaken by Brighton & Hove during 2020
To determine the 6 AQMAs declared in 2020 a detailed air quality assessment accompanied the report to Environment Transport and Sustainability Committee.
This was in advance of a report outlining intention to expand the cities Ultralow Emission Zone. The report can be updated prior to the AQAP being considered by ETS committee.
QA/QC of diffusion tube monitoring
Gradko International diffusion tubes have been consistently used for many years by Sussex Local Authorities using the 20% TEA in water method.
2020 diffusion tube monitoring covered eleven periods and most of these alternated between four- and five-week exposure periods. The notable exception being one longer period from 8 April 2020 during the COVID travel restrictions, prior to the laboratory shutdown.
Accreditation of the diffusion tube monitoring method like previous years is as follows:
Diffusion tube annualisation
Annualisation is required for any site with data capture less than 75% but greater than 25%. For 2020 5 diffusion tubes sites required annualisation these are detailed in Table C.2.
Diffusion tube bias adjustment factors
The diffusion tube data presented within the 2020 ASR have been corrected for bias using an adjustment factor. Bias represents the overall tendency of the diffusion tubes to under or over-read relative to the reference chemiluminescence analyser or regulatory monitor.
LAQM.TG16 provides guidance regarding the application of a bias adjustment factor to correct diffusion tube monitoring. Triplicate co-location studies can be used to determine a local bias factor based on the comparison of diffusion tube results with data taken from NOx/NO2 continuous analysers. Alternatively, the national database of diffusion tube co-location surveys provides bias factors for the relevant laboratory and preparation method.
Brighton & Hove have applied a local bias adjustment factor of 0.95 to the 2020 monitoring data using triplicate co-location factor derived from automatic analyser BH10 on North Street.
This site in AQMA 1 and the ULEZ is most representative of the local area. The 2020 local bias correction factor is consistent with those used by Brighton & Hove over the past decade. This is important given that trend graphs are presented since 2008 or 2010. A summary of bias adjustment factors used by Brighton & Hove over the past 5 years is presented in Table C.1.
Table C.1 – Bias adjustment factor
View and download Table C.1
NO2 Fall-off with Distance from the Road
Brighton & Hove has ensured that monitoring locations are representative of exposure on a building line façade or equal distance between the traffic sources and receptor.
Kerbside monitors in AQMA1 declared for the hourly mean assess transient exposure to pollutants above busy footways. Some of Brighton & Hove’s monitors are at background locations or are complaint with standards and therefore do not require an NO2 fall-off with distance calculation. No diffusion tube NO2 monitoring locations within Brighton & Hove required distance correction during 2020.
In practice the NO2 fall-off with distance calculator works best for open field settings and is less suited to confined spaces, the lee side of buildings and street canyons, that are the typical scenario for significant portions of Brighton & Hove’s AQMAs declared in 2020.
QA/QC of automatic monitoring
TRL carry out the QA/QC on behalf of Brighton & Hove Council for the monitoring stations BH6 and BH10 on Lewes Road and North Street.
Routine instrument calibrations are conducted approximately once per fortnight, which involve zero and span checks, a written record of the gas analyser diagnostics and a general visual inspection of all equipment is undertaken. There is a written operating procedure and a calibration record sheet is completed at every site visit.
Data retrieval and daily data checking
Data from the monitoring station is retrieved directly via a Siemens TC35i GSM modem at 8-hourly intervals.
The data is then stored on Envista Arm software hosted at TRL. This was used to retrieve, check and archive data. TRL's internal QA/QC procedures require all data to be backed up on a secure server and all documentation associated with each site to be uniquely identified and securely stored to provide an audit trail.
Daily data inspections are undertaken during office hours using the facilities of the Data Management System. Initial observations of the Management System indicate whether the site has been contacted during its nominated ‘poll time’ overnight. If this has not been successful a manual poll of the site may be required. If this is not successful further investigation of the communications integrity will be required to establish contact with the site modem and data logger.
Three day plots of recorded data are viewed for the requested site, and these are inspected and assessed for continuity, validity, minimum and maximum values, date and time, power failures and general integrity.
All anomalies are recorded on the Daily Check log, as required. Any anomalies or queries arising from daily inspection of data, or system operation, are brought to the attention of the Project Manager who will evaluate the situation, and initialise any necessary action.
In the event that the PM is not available, contact will be made with the next available senior person within the monitoring team. Any issues identified with equipment operation will be referred to the client for attention within 24 hours (excluding weekends).
On a weekly basis, data are examined using summary statistics and outlier analysis to establish data validity. If unusual data episodes are recorded, these would be routinely examined over longer data periods to establish their impact on trends but would also be cross referenced with data peaks and troughs recorded at other national monitoring stations.
In addition, integrity and validity of data logger clock times are checked, and any significant errors recorded in the Data Management System logbook. All site data recorded through the Data Management System is archived on TRL’s Network. The data is backed up daily, and the TRL IT Department maintains these data within their long-term and secure archives. This secures all data in the event of any system failure.
Data calibration and ratification
Data is ratified as per Automatic Urban Rural Network (AURN) recommended procedures. The calibration and ratification process for automatic gas analysers corrects the raw dataset for any drift in the zero baseline and the upper range of the instrument. This is done using Evista-based calibration and ratification which incorporates the zero and span check information from the calibration visits.
The zero-reading recorded during the calibration visits is used to adjust any offset of the baseline of the data. The difference between the span value obtained between one calibration visit and the next visit is used to calculate a factor. This change is assumed to occur at the same rate over the period between calibrations and as such the factor is used as a linear data scaler. This effectively results in the start of the period having no factor applied and the end of the period being scaled with the full factor with a sliding scale of the factor in-between.
After applying the calibration factors, it is essential to screen the data, by visual examination, to see if they contain any unusual measurements or outliers. Errors in the data may occur because of equipment failure, human error, power failures, interference, or other disturbances.
Data validation and ratification is an important step in the monitoring process. Ratification involves considerable knowledge of pollutant behaviour and dispersion, instrumentation characteristics, field experience and judgement. On completion of this data correction procedure, the data is converted to hourly means and provided to Brighton & Hove City Council at quarterly intervals and a calendar year annual report is prepared.
Table C.2 – Annualisation summary - concentrations presented in µg/m3
View and download Table C.2
Table C.3 – Local bias adjustment calculation
View and download Table C.3
Overall Diffusion Tube Precision: Good.
Overall Continuous Monitor Data Capture: Good.
A single local bias adjustment factor has been used to bias adjust the 2020 diffusion tube results.