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The COVID-19 lockdown measures gradually implemented in Lombardy (northern Italy) from 23 February 2020 led to a downturn in several economic sectors with possible impacts on air quality. Several communications claimed in the first weeks of March 2020 that the mitigation in air pollution observed at that time was actually related to these lockdown measures without considering that seasonal variations in emissions and meteorology also influence air quality. To determine the specific impact of lockdown measures on air quality in northern Italy, we compared observations from the European Commission Atmospheric Observatory of Ispra (regional background) and from the regional environmental protection agency (ARPA) air monitoring stations in the Milan conurbation (urban background) with expected values for these observations using two different approaches. On the one hand, intensive aerosol variables determined from specific aerosol characterisation observations performed in Ispra were compared to their 3-year averages. On the other hand, ground-level measured concentrations of atmospheric pollutants (NO2, PM10, O3, NO, SO2) were compared to expected concentrations derived from the Copernicus Atmosphere Monitoring Service Regional (CAMS) ensemble model forecasts, which did not account for lockdown measures. From these comparisons, we show that NO2 concentrations decreased as a consequence of the lockdown by −30 % and −40 % on average at the urban and regional background sites, respectively. Unlike NO2, PM10 concentrations were not significantly affected by lockdown measures. This could be due to any decreases in PM10 (and PM10 precursors) emissions from traffic being compensated for by increases in emissions from domestic heating and/or from changes in the secondary aerosol formation regime resulting from the lockdown measures. The implementation of the lockdown measures also led to an increase in the highest O3 concentrations at both the urban and regional background sites resulting from reduced titration of O3 by NO. The relaxation of the lockdown measures beginning in May resulted in close-to-expected NO2 concentrations in the urban background and to significant increases in PM10 in comparison to expected concentrations at both regional and urban background sites.

As part of the ongoing key comparison BIPM.QM-K1, a comparison has been performed between the ozone standard of the European Commission maintained by the Joint Research Centre (JRC) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM). The instruments have been compared over a nominal ozone amount-of-substance fraction range from 0 nmol/mol to 500 nmol/mol. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A growing number of companies have started commercializing low-cost sensors (LCS) that are said to be able to monitor air pollution in outdoor air. The benefit of the use of LCS is the increased spatial coverage when monitoring air quality in cities and remote locations. Today, there are hundreds of LCS commercially available on the market with costs ranging from several hundred to several thousand euro. At the same time, the scientific literature currently reports independent evaluation of the performance of LCS against reference measurements for about 110 LCS. These studies report that LCS are unstable and often affected by atmospheric conditions—cross-sensitivities from interfering compounds that may change LCS performance depending on site location. In this work, quantitative data regarding the performance of LCS against reference measurement are presented. This information was gathered from published reports and relevant testing laboratories. Other information was drawn from peer-reviewed journals that tested different types of LCS in research studies. Relevant metrics about the comparison of LCS systems against reference systems highlighted the most cost-effective LCS that could be used to monitor air quality pollutants with a good level of agreement represented by a coefficient of determination R2 > 0.75 and slope close to 1.0. This review highlights the possibility to have versatile LCS able to operate with multiple pollutants and preferably with transparent LCS data treatment.

A prototype of an automatic static volumetric method based on the injection of a pure compound by means of a loop instead of a manual syringe was constructed, fitting for both laboratory use and field applications. The crucial point, the evaluation of the loop volumes, was solved developing two techniques allowing traceability to SI units. Gas mixtures of nitrogen monoxide (NO) in nitrogen in the 10−9 V/V range and carbon monoxide (CO) in air in the 10−6 V/V range were generated and successfully compared to other primary calibration techniques. Relative expanded uncertainties (k=2) of 1.1% (compared to 0.8% of the manual static volumetric method [1]) for NO gas mixtures and 0.3% CO gas mixtures were estimated.

This paper presents the results of a feasability study for the preparation and certification of reference materials (RMs) for nitrogen dioxide (NO(2)) and sulfur dioxide (SO(2)) in diffusive samplers. RMs for NO(2) were prepared by exposure to gas mixtures in a chamber while the RMs for SO(2) were prepared by liquid spiking. Certification of RMs for NO(2) was found feasible with a certified uncertainty of 5.8% and a proposed shelf life of 5 years. The uncertainty was calculated with contribution from the homogeneity of preparation, stability and transport of the CRMs and from an external verification of the certified value. To reach 5.8% of uncertainty, the contribution of the differences between the results of analysis by ion chromatography and colorimetry must be eliminated. It is proposed to solve this by pre-extracting the samplers with water before analysis. The results of this study indicate that the samplers are stable for at least two years before and after exposure when stored in a refrigerator. By contrast, the certification of RMs for SO(2) was found to not be feasible due to instability problems. This instability was attributed to reaction of sulfate on the walls of the samplers. Alternatively, the preparation of RMs by simultaneous exposure to SO(2) and NO(2) has been tested. Satisfying homogeneities has been reached both for NO(2) and SO(2).

Carbon monoxide (CO) is reported to mainly be emitted from industries, transportation, and burnings for various usages. Its atmospheric lifetime varies from weeks to months, depending on the mixing ratio of the highly reactive hydroxyl radical. Even though the ambient level of CO varies as a function of regional sources, the mixing ratio ranges from 30 nmol/mol to 300 nmol/mol at the marine boundary layers and from 100 nmol/mol to more than 500 nmol/mol in urban areas(1). In order to study temporal trends and regional variations of the level of CO, the National Oceanic & Atmospheric Administration/Earth System Research Laboratory-Global Monitoring Division (NOAA/ESRL-GMD(2)) has played a key role as the designated Central Calibration Laboratory (CCL) within the frame of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) program. NOAA/ESRL-GMD provides natural air standards, analyzed for CO, to WMO GAW participants. Since the structure of WMO traceability chain appears hierarchical and explicit all over the world, WMO intends to improve the CO measurement compatibility to up to 2 ppb (in case of extensive compatibility goal: 5 ppb, GAW report No. 213(3)) in order to ensure compatibility through the GAW network. Nevertheless, accurate measurement of CO at an ambient level has proven to be difficult due to the lack of stability in cylinders. For these reasons, it is necessary that measured results are compared among the values assigned by various NMIs. This key comparison was initially proposed to be aimed at a CO/N2 standard in the 2010 CCQM meeting by KRISS. With participation of FMI, NOAA, and Empa, a modified scheme of CO/air standards was developed for the purpose of atmospheric observations and co-operative support to WMO/GAW activities. Therefore, the purpose of the comparison is to support the measurement capability of CO at an ambient level of 350 nmol/mol. Further, this key comparison is expected to contribute to the establishment of traceability to a single scale of CO between NMIs by means of harmonizing the results from different national standards. The Empa result lies in a different report. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Monitoring personal exposure to particle matter (PM2.5) in ambient air requires performing measurements using portable monitors. In this work, the portable nephelometer SidePak AM510 Personal Aerosol Monitor manufactured by TSI Inc. was evaluated against a Tapered Element Oscillating Microbalance (TEOM) equipped with a Filter Dynamics Measurements System (FDMS). Conventionally, the SidePak is calibrated with respect to the Arizona Road Test Dust and then multiplied by an environmental calibration factor to yield mass concentration. To adapt this calibration to specific field conditions, we present an implementation of this calibration by introducing a growing factor correction which takes into account relative humidity and the dry and wet portions of the refractive index estimated from TEOM-FDMS measurements. PM2.5 sampling with several SidePaks AM510 was carried out in background and rural sites in the Po Valley (Italy). Modeled SidePak data were plotted vs. reference TEOM-FDMS data which show a good agreement., JRC.H.2-Air and Climate

This study presents an evaluation of the extent of differences between measurements performed by O(3) and NO(2) diffusive samplers and by the reference methods for diffusive samplers commercially available. The tests were performed in an exposure chamber under extreme conditions of controlling factors and under field conditions. For NO(2), the results of the laboratory experiments showed that most of the diffusive samplers were affected by extreme exposure conditions. The agreement between the samplers and the reference method was better for the field tests than for the laboratory ones. The estimate of the uptake rate for the exposure conditions using a model equation improved the agreement between the diffusive samplers and the reference methods. The agreement between O(3) measured by the diffusive samplers and by the reference method was satisfactory for 1-week exposure. For 8-hour exposures, the diffusive samplers with high uptake rates quantified better the O(3) concentration than the samplers with low uptake rates. As for NO(2), the results of the O(3) field tests were in better agreement with the reference method than the ones of the laboratory tests. The field tests showed that the majority of diffusive samplers fulfils the 25% uncertainty requirement of the NO(2) European Directive and the 30% uncertainty requirement of the O(3) European Directive for 1-week exposure.

Accurate measurements of sulphur dioxide at the concentrations found in ambient air have become essential to support monitoring and legislation concerned with air quality. In general, the primary element of quality assurance for field instruments is regular calibration using certified gas mixtures. The concentration range chosen for this Key Comparison (240 nmol/mol to 320 nmol/mol) is defined by appropriate European standards and is typical of similar levels used around the world. The travelling standards used for the comparison were prepared commercially by a supplier with a proven track record of preparing stable mixtures of the relevant gases. The coordinating laboratory (NPL) carried out stability checks on the mixtures and determined the amount fraction using a primary gravimetric permeation facility. These data were used to determine the drift rate (and uncertainty) of each standard. The results for the 11 participants in CCQM-K26.b and the one participant in CCQM-P50.b are presented in this report. Degrees of equivalence have been calculated based on a reference value (corresponding to the KCRV) derived from the primary gravimetric facility used by the coordinating laboratory. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

We report a pilot study organized within the Consultative Committee for Amount of Substance (CCQM), in which the ozone reference standards of 23 institutes have been compared to one common reference, the BIPM ozone reference standard, in a series of bilateral comparisons carried out between July 2003 and February 2005. The BIPM, which maintains as its reference standard a standard reference photometer (SRP) developed by the National Institute of Standards and Technology (NIST, United States), served as pilot laboratory. A total of 25 instruments were compared to the common reference standard, either directly (16 comparisons) or via a transfer standard (9 comparisons). The comparisons were made over the ozone mole fraction range 0 nmol/mol to 500 nmol/mol. Two reference methods for measuring ozone mole fractions in synthetic air were compared, thanks to the participation of two institutes maintaining a gas-phase titration system with traceability of measurements to primary gas standards of NO and NO2, while the 23 other instruments were based on UV absorption. In the first instance, each comparison was characterized by the two parameters of a linear equation, as well as their related uncertainties, computed with generalized least-squares regression software. Analysis of these results using the Birge ratio indicated an underestimation of the uncertainties associated with the measurement results of some of the ozone standards, particularly the NIST SRPs. As a final result of the pilot study, the difference from the reference value (BIPM-SRP27 measurement result) and its related uncertainty were calculated for each ozone standard at the two nominal ozone mole fractions of 80 nmol/mol and 420 nmol/mol. Main text. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCQM.