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Atmospheric day and night concentrations of particulate organic nitrates (PON) and several other air pollutants were measured in the summer 1995 over an open-land area in Denmark. The sampling of PON was evaluated comparing 24 h samples with two sets of 12 h samples. These results indicate that the observed low contribution of PON to NOy is real and not the result of an extensive loss during the sampling. Empirical relationships between the vapour pressure and chemical formula of organic compounds were established in order to evaluate the gas/particle distribution of organic nitrates. A positive correlation between the PON to NOz ratio and the inverse temperature may indicate that the organic nitrates associated with particles also may be present in the gas phase. The observed day and nighttime levels of PON were of the same magnitude, although the day to night ratio varied from 0.4 to 4.4.

Formic and acetic acid measured as daily averages in 1993–1994show equal and highly correlated concentrations up to 3 ppb in the summer(May–August). In the winter (October–March) the formicacid/acetic acid ratio was 0.6 and the formic acid concentrations wereusually below 1 ppb. In winter the carboxylic acids correlate withOx, NOy, SO2 and particulatesulphur. The main sources are suggested to be ozonolysis of anthropogenicalkenes and reactions between peroxyacetyl radicals and RO2radicals. In spring–summer the carboxylic acids correlate withO3, Ox, HNO3, PAN,NOy, SO2, particulate sulphur and temperature.In addition to the sources of the winter a contribution from ozonolysis ofbiogenic alkenes is likely. Quite similar formic acid/acetic acid ratios forall wind directions suggest that the source(s) are atmospheric oxidationprocesses distributed over large areas. The highest concentrations occurringfor winds from east to south and the correlation with e.g., particulatesulphur indicate chemical production in polluted air masses during longrange transport.

Traffic in cities and on highways is an important contributor to NO y atmospheric pollution in open areas. In this situation both the concentration and composition of NO y compounds show a wide variation and are dependent on meteorological and atmospheric chemical conditions. The proportion of NO z compounds (HNO 3 + nitrate + PAN + PPN + N 2 O 5 + organic nitrates) increases while that of NO x decreases with increasing ozone concentrations. The dry deposition velocity of NO 2 was determined to be 0.2 cm s −1 above vegetation. The dry deposition contribution of the different NO y compounds was evaluated. The possiblity that a significant contribution is caused by a group of unidentified NO y compounds cannot be excluded. Therefore, future investigations of atmospheric pollution of sensitive ecosystems, at conditions with a relatively high atmospheric content of NO y compared to that of NH 3 , ought to take into consideration the possible contribution from unidentified NO y compounds. This also implies that atmospheric research into the identity, occurrence, sources and sinks of these compounds—as well as further developments of sampling and analytical methods—should be given a high priority.

Atmospheric concentrations of organochlorine pesticides (OCs), polybrominated diphenyl ethers (PBDEs) and polychloronaphthalenes (PCNs) were measured for the first time in Nuuk, Greenland in 2004 and 2005. The annual mean concentrations af the measured OCs were: α-HCH 20.2 pg m-3, Υ-HCH (lindane) 5.1 pg m-3, endosulfan 4.8 pg m-3 and dieldrin 1.9 pg m-3. Concentrations of ∑-chlordanes, DDEs and heptachlor epoxide were generally similar and lower than those of α-HCH and Υ-HCH. The concentrations of most chlorinated pesticides did not show any clear seasonal variation, with the exception of Υ-HCH, which had maximum concentration in August in both years. The average annual mean for ΣPBDEs was 1.14 ± 0.81 pg m-3. The predominant congeners measured in Nuuk were BDE-47 and BDE-99 followed by BDE-100, -153 and -28, indicating the use of penta-BDE technical products as the main source. A clear seasonal variation of PBDE concentrations was observed with maximum concentrations occurring in the summer months.The ∑PCNs concentrations ranged between 0.062 and 0.258 pg m-3 with an annual mean concentration of 0.161 ± 0.0004 pg m-3. The PCNs profile was dominated by the tetra-PCNs(74% of the annual mean) and the penta-PCNs (18% of the annual mean). A seasonal trend for ∑PCNs was not observed.Atmospheric concentrations of the investigated compounds were correlated with temperature and anthropogenic CO in order to obtain information about their transport pattern. Positive correlations were found between CO and chlordanes, p, p' DDE and trifluralin, while a negative correlation was found for Υ-HCH. A significant correlation with temperature variations was found for dieldrin, heptachlor epoxide, α-HCH, Υ-HCH, BDE-47, BDE-99 and tetra-PCNs, which indicates that re-emission of these compounds from previously contaminated surfaces as an important factor for the observed variations in concentrations.