Studies of the properties of particulate matter in the UK atmosphere

The studies on physical and chemical properties of airborne particulate matter were carried out in the UK atmosphere. Aerosol samples were collected at the Elm Road Observatory Site and Harwell representing urban background and rural area, respectively. The chemical components of both PM$_2$$_.$$_5$ and PM$_2$$_.$$_5$$_-$$_1$$_0$ were mainly analysed for carbonaceous compounds, sulphate, nitrate, chloride and oxalate. Size distributions of aerosol components were investigated in conjunction with the study of ammonia gas to stabilise the semivolatile species in atmospheric particles. Concentration composition of carbonaceous compounds (organic and elemental carbon - OC and EC) in particulate matter clearly observed higher value at urban background than those at rural area. The OC/EC minimum ratio of 0.35 was used to distinguish between primary and secondary OC as EC was a good indicator of primary sources. Sulphate and nitrate showed the good relationship, indicating that two species undergo similar formation and removal processes in atmosphere. Chloride was commonly originated from marine aerosol with the weak correlation observed with other major species. Oxalate is highly focused specie in this study as there is rarely available data in the UK. The good correlation and the similar pattern of size distribution between oxalate and sulphate suggest that their formation pathway formed from the same atmospheric processes. The excess ammonia gas supplied during the air sampling could be stablilsed and yielded the higher concentrations of nitrate and chloride which were expected in the forms of ammonium salts. In contrast, oxalate in ambient air was exhibited the discordant behaviour in this experiment. Our trajectory analysis suggests the important precursor sources of oxalate were from continental area associated with the high atmospheric pollutants

Receptor modelling of secondary and carbonaceous particulate matter at a southern UK site

Complementary approaches have been taken to better understand the sources and their spatial distribution for secondary inorganic (nitrate and sulphate) and secondary organic aerosol sampled at a rural site (Harwell) in the southern United Kingdom. A concentration field map method was applied to 1581 daily samples of chloride, nitrate and sulphate from 2006 to 2010, and 982 samples for organic carbon and elemental carbon from 2007 to 2010. This revealed a rather similar pattern of sources for nitrate, sulphate and secondary organic carbon within western/central Europe, which in the case of nitrate, sulphate, organic carbon and secondary organic carbon, correlated significantly with EMEP emissions maps of NOx, SO2, and VOC respectively. A slightly more southerly source emphasis for secondary organic carbon may reflect the contribution of biogenic sources. Trajectory clusters confirm this pattern of behaviour with a major contribution from mainland European sources. Similar behaviours of, on the one hand, sulphate and organic carbon and, on the other hand, EC and nitrate showed that the former are more subject to regional influence than the latter in agreement with the slower atmospheric formation of sulphate and secondary organic aerosol than for nitrate, and the local/mesoscale influences upon primary EC. However, careful analysis of back trajectories and Concentration Field Maps indicates a strong contribution of mainland European sites to EC concentrations at Harwell. In a separate study, measurements of sulphate, nitrate, elemental and organic carbon were made in 100 simultaneously collected samples at Harwell and at a suburban site in Birmingham (UK). This showed a significant correlation in concentrations between the two sites for all of the secondary constituents, further indicating secondary organic aerosol to be a regional pollutant behaving similarly to sulphate and nitrate

International Comparison CCQM-K51 - Carbon Monoxide (CO) in Nitrogen (5 µmol mol-1)

The first key comparison on carbon monoxide (CO) in nitrogen dates back to 1992 (CCQM-K1a). It was one of the first types of gas mixtures that were used in an international key comparison. Since then, numerous national metrology institutes (NMIs) have been setting up facilities for gas analysis, and have developed claims for their Calibration and Measurement Capabilities (CMCs) for these mixtures. Furthermore, in the April 2005 meeting of the CCQM (Consultative Committee for Amount of Substance) Gas Analysis Working Group, a policy was proposed to repeat key comparisons for stable mixtures every 10 years. This comparison was performed in line with the policy proposal and provided an opportunity for NMIs that could not participate in the previous comparison. NMISA from South Africa acted as the pilot laboratory. Of the 25 participating laboratories, 19 (76%) showed satisfactory degrees of equivalence to the gravimetric reference value. The results show that the CO concentration is not influenced by the measurement method used, and from this it may be concluded that the pure CO, used to prepare the gas mixtures, was not 13C-isotope depleted. This was confirmed by the isotope ratio analysis carried out by KRISS on a 1% mixture of CO in nitrogen, obtained from the NMISA. There is no indication of positive or negative bias in the gravimetric reference value, as the results from the different laboratories are evenly distributed on both sides of the key comparison reference value.JRC.H.2-Air and Climat