AQ ereporting. Clarification on technical issues

Transcription

1 AQ ereporting Clarification on technical issues V4.1 24/04/2016 Based on EEA and ETC/ACM experiences to date, several technical questions have been identified during the compilation and handling AQ data reported under the IPR. The present document briefly summarises six of the issues which were discussed at the EIONET Air Quality meeting (Ljubljana - October 2015) and at the 14 th IPR Meeting (Copenhagen November 2015) and the interpretation followed by the EEA in implementing the AQ ereporting system. 1 Rounding The IPR Guidance Document (part 1 p.10) indicates that assessment data have to be compared to the environmental objectives (i.e. limit value, target value, etc.) in the same numeric accuracy as is used for the specification of the environmental objective in the Directive. This rule is strictly followed for compliance checking. However some data presentation such as graphs and maps might require to use higher accuracy and therefore rounding rules. This is particularly the case for mapping the data coloured according to their values. For compliance checking, the IPR Guidance Document rounding rules are strictly applied. In case of data presentation which might require to use different classes of values, the classes, accuracy and rounding adopted for the different EEA outputs (such as AQ reports, maps and viewers) are listed in Annex the present document. 2 Data capture, time coverage and data coverage The data capture, as defined in the IPR Guidance Document (part 1 pp.44-46) is the proportion (%) of valid measurements obtained within the measurement period defined by time coverage. For ozone measurements, the measurement period must be divided into summer and winter seasons. The data capture DC in a given averaging period (e.g. a year) is calculated as follows DC = N valid / N total * 100 % Where N valid N total number of valid hourly/daily measurements in the measurement period (defined by the time coverage) total number of hours/days in that measurement period. The time coverage (TC) is the proportion (%) of a calendar year (or summer season (April - September) in the case of indicative ozone measurements), for which measurements were originally planned. The time coverage for a given averaging period (year / season ) is calculated as follows: TC = N planned / N averaging period * 100 % 1

2 Where N planned N averaging_period number of hours/days on which measurements were planned to take place total number of hours/days in the given averaging period (e.g. year/season) Issue The ereporting system as described in the IPR Guidance Document and implemented by the EEA system does not allow to make the difference between planned missing (or invalid or not reported at all) data and unplanned missing (or invalid or not reported at all) data. If data is not provided the system can only assume that the data is missing. The rules on time coverage and data capture requirements may therefore lead to ambiguous cases. This is illustrated below using the example given in the IPR Guidance Document (part 1 p.48 4): BaP daily Situation a Minimum time coverage 33% Planned measurement time 156 days Planned measurement time > time coverage 100 * 156 / 365 = 42.74% > 33% N valid 132 days Data capture 100 * 132 / % rounded to 85% Valid Situation b If we modify the planned measurement time from 156 to, say, 200 days, but have at the end of the monitoring period the same number of valid measurement (132) this becomes Minimum time coverage 33% over the year Planned measurement time 200 days Planned measurement time > time coverage 100 * 200 / 365 = 54.79% > 33% N valid 132 days Data capture 100 * 132 / % < 85% Not valid although same number of valid measurements and time coverage criteria fulfilled In practice, the system calculates DC and TC as follows: Data Capture DC = count count count count :;< Time Coverage TC = count count count :;< [Interval] In order to avoid ambiguities, the system also calculate the data coverage (DCov) Data Coverage DCov = count [Interval] = TC DC 2

3 In case of continuous measurement (TC = 100%), DC = DCov. 3 Maintenance and calibration 1. Should the 5% for maintenance and calibration (and therefore the 85% data capture criteria IPR Guidance Document part 1 p.47) still apply when raw data are aggregated to another averaging time? For example hourly data aggregated into daily data used to check compliance like for PM10. Applying the 75% rule for calculating the daily values and the 85 % of daily values for the number of exceedance means that 64 % of hourly values are sufficient to calculate valid statistics. The 5% for maintenance and calibration (and therefore the 85% data capture criteria) is still applied when raw data are aggregated to another averaging time. 2. Should the 5% for maintenance and calibration also be considered when time coverage are <100% (discontinuous measurement e.g. BaP)? Or should it be proportional to the time coverage? For compliance checking the 5% for maintenance and calibration is applied. In case of assessment (outside compliance), the user may set his own criteria for accepting or rejecting a statistical value based on data capture, time coverage and/or data coverage. The present practice at the EEA is to apply a 75% data coverage for all measurements unless otherwise stated. 4 Validity flag and verification status Validity flags associated to the data are (IPR Guidance Document part 1 p.41) 1 valid 2 valid, but below detection limit measurement value given 3 valid, but below detection limit and number replaced by 0.5*detection limit -99 not valid due to station maintenance or calibration -1 not valid due to other circumstances or data is simply missing. Verification flags associated to the data are: 1 verified 2 preliminary verified 3 not verified The Directive foresees minimum percentages of valid values for calculating statistics relevant for compliance checking. For the E1a submission (annual submission of data related to the reporting year Y-1 to be done by end September of the following year) all data are supposed to be fully verified. This is not the case for the data transferred under E2a (UTD) which can be associated to different verification levels (usually they are not or partly verified). In the implemented ereporting system, both E1a data and E2a data are merged into a single database. Verification flags and the origin of the data remain associated to the values. Because only the last transmitted version of the data sets is kept within the database, this mixed origin should not 3

4 raise any issue: the UTD data (E2a with verification flag set to not or partly verified) should normally be overwritten by the official delivery submitted later (E1a with verification flag set to fully verified). Some special cases may however happen: - the country does not submit officially through E1a data which were previously transmitted as UTD (E2a). - the country, for whatever reason, has not proceeded to the verification of all data submitted in E1a. As statistics are calculated from all data, it might happen in these cases than unverified or partly verified data are used for calculating compliance statistics. In case they are calculated with data other than fully verified the statistics are flagged as unverified value even for one single unverified data and are not used, neither for compliance checking nor for producing EEA outputs (unless otherwise stated e.g. in some data and statistics viewers). 5 AEI calculation method The table below presents the official method to calculate the AEI. Official method (AQ Directive) Select PM2.5 SamplingPoints set up for AEI Calculate the annual mean for each SamplingPoint and corresponding data capture for year X, X-1, X-2 Reject those SamplingPoints with data capture <85 % Repeat for each selected PM2.5 SamplingPoint Calculate the annual average AEI contribution for the years X, X-1 and X-2. The average concentration for each year is calculated as the simple arithmetic average of the values for retained locations. Calculate the AEI as the simple arithmetic average of the values for the three years involved. Rounding to integer if above 10µg/m3, to 1 decimal if below 10 µg/m3 to done at this level Issue The official methodology leaves room for technical interpretation (different set of time series over the 3 year period, time series rejected ). From the experience in the past, it appears that (from ETC/ACM): - not all MS have delivered an "official" AEI-value; - when AEI has been reported MS may not report over the same 3-year period; - a list of "official" AEI-monitoring stations as selected by the MS is not available for all countries The methodology used by ETC/ACM until now for assessment, not compliance checking, is as follows: - select for a three-year period all operational (sub)urban background stations (operational is defined as having a data coverage of 75% or more) - calculate for each year a national average from the station annual means - next average this for the three years - in none of these step numbers have been rounded. Only when presenting the AEI-values, numbers should be rounded to one decimal. 4

5 This calculation procedure is similar as the one described in the AQD, only the selection of stations differs but also the percentage of valid data which is the one used by the EEA for assessment purposes. For compliance evaluation, the threshold of 85% would be applied. For compliance checking, the AEI shall be calculated on the official AEI sampling points declared by the countries and fully apply the methodology as defined in the AQ Directive and in the IPR Guidance Document (Part 1 p.13). For assessment purposes (outside compliance checking), the EEA might follow the methodology followed over the past years by the ETC/ACM. 6 CSI4 Exceedance of air quality limit values in urban areas The methodology used at present to calculate the EEA core set indicator on exceedance of air quality limit values in urban areas is as follows: For PM10, PM2.5, O 3, NO 2 and SO 2 only stations with data time coverage of at least 75 % per calendar year are used. That is, in the case of daily values, having more than 274 valid daily values per calendar year (or 275 days if leap year). And in the case of hourly values, having more than 6570 valid hourly values per calendar year (or 6588 hours if leap year). For B(a)P the minimum data time coverage accepted is 14 % (51 days), according to the data quality objectives related to indicative measurements in the Directive 2004/107/EU (EU, 2004). For every year, each city i in country j, and every pollutant, the total number of urban or suburban traffic stations (nit) and the total number of urban or suburban background stations (nib) are obtained. P tj % of the total population of the city (Pop i ) is proportionally assigned to each of the traffic stations and P bj % of Pop i is proportionally assigned to each of the background stations. So, every traffic station has an allocated population equal to ((P tj / 100) * Pop i / n it ) and every background station has an allocated population equal to ((P bj /100) *Pop i / n ib ). Issue It happens mostly for PM that two or more methods can be used at the same station. At the moment, the values associated to both of them are taken into account in the calculation of the index, provided they both fulfil the data coverage criteria. This introduces a bias into the results. This issue does not only apply to CSI4 but might also be relevant for other products. Priority will be given to the sampling point used for compliance checking provided its data coverage meets the criteria of 75%. Otherwise the other sampling point will be used. 5

6 Annex: classes and rounding used for the different pollutants and metrics NO2 annual mean - <=20 20< - <=30 30< - <=40 40< - <=50 50< - SO2 annual mean - <=5 5< - <=10 10< - <=20 20< - <=25 25< - PM10 annual mean - <=20 20< - <=31 31< - <=40 40< - <=50 50< - PM10 P <=20 20< - <=40 40< - <=50 50< - <=75 75< - PM2.5 annual mean - <=10 10< - <=20 20< - <=25 25< - <=30 30< - CO maximum daily eight hour mean - <= < - <= < - <= < - <= < - (Rounding to one decimal for all classes) C6H6 annual mean <= < - <= < - <= < - <= < - (Rounding to one decimal for all classes) O3 maximum daily eight hour mean - <=60 60< - <=80 80< - <= < - O3 P <=80 80< - <= < - <= < - <= < - BaP annual mean - <= < - <= < - <= < - <= < - (Rounding to two decimals for all classes) 6

7 Pb annual mean <= < - <= < - <= < - <= < - (Rounding to two decimals for all classes) Cd annual mean <=1.0 1< - <=2 2< - <=5 5< - <=8 8< - As annual mean <=1 1< - <=3 3< - <=6 6< - <=9 9< - Ni annual mean <=5 5< - <=10 10< - <=20 20< - <=30 30< - 7