Martin Ferm

Method for determination of atmospheric ammonia

Abstract Determination of ammonia in air is complicated by interference from particle-borne ammonium ions. This problem can however be solved by utilizing the well-known fact that when ambient air passes through a tube, gas molecules diffuse much more quickly than particles to the tube wall. The method presented here is based on both theoretical considerations and practical tests.

A sodium carbonate coated denuder for determination of nitrous acid in the atmosphere

Abstract A denuder technique for sampling and analysing nitrous acid at sub ppb levels in air is described. After sampling, the sodium carbonate coated denuder is leached in water, and the NO−2 concentration is determined spectrophotometrically. Field tests show that PAN is partly sorbed and hydrolized to nitrite in the sodium carbonate layer. It seems as HNO2 also can be formed by heterogeneous reactions between NO and NO2 at the denuder wall. These sampling artifacts were overcome by sampling with two or three denuders in series. The presence of PAN deteriorates the detection limit, which during optimal conditions is about 0.5 nmole m−3 (0.01 ppb). The method is therefore not recommended for measurements in background air, where HNO2 concentrations normally are low compared to PAN concentrations.

Seasonal variations in aerosol concentrations and compositions in the Nepal Himalaya

This paper summarizes a 15-month long study (September 1996–November 1997) on water soluble components (Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3−, and SO42−) in atmospheric aerosols conducted at a remote Himalayan site and a rural Middle-Mountain site in Nepal. Most of the species sampled behave similarly in terms of seasonal and short-term variations. The aerosol concentrations were low during the second half of the monsoon and post-monsoon seasons and gradually increased during the winter season. Aerosol concentrations in some samples were up to 20 times higher during the pre-monsoon and early-monsoon seasons than they were in post-monsoon. The seasonal variations are clearly related to variations in atmospheric circulation. The high concentrations during the pre-monsoon season are attributed to regional scale valley wind systems and the maximum concentrations at both sites coincide with maxima in the local wind speed record. Occasional shifts in the large-scale circulation resulted in dramatic fluctuations in aerosol concentrations during the pre-monsoon and early monsoon seasons. In the middle of May the large-scale circulation changed from westerly to south-easterly monsoon in the Himalaya. The summer monsoon circulation brought considerable amounts of pollution to the sites from southeast. Precipitation played an important role in short-term (few samples, e.g., during the late winter at the Himalayan site) to longer-term (several samples, e.g., after mid-June at both sites) reduction in the aerosol concentrations, while the lack of precipitation in the pre-monsoon and early monsoon supported a gradual build-up of pollutants in the atmosphere. During the pre-monsoon and early monsoon, when concentrations were elevated at both sites, they were often higher at the remote Himalayan site than at the middle mountain site. A pollution layer in the monsoon circulation due to dry convective rise of pollutants at distant sources and horizontal upper air transport by monsoon flow could have caused these elevated concentrations.

A Na2CO3-coated denuder and filter for determination of gaseous HNO3 and particulate NO−3- in the atmosphere

Abstract HNO3 is present in air in the gas as well as the particle phase. The gas phase is difficult to sample due to its extremely high affinity for most materials. When particulate nitrate is removed by filtration it may release gaseous HNO3. These difficulties can be overcome by first removing the gas phase in a Na2CO3-coated denuder and then by collecting the particle phase on a Na2CO3-impregnated filter. After sampling they are separately leached with water and the nitrate content is determined by ion chromatography. The detection limit for 24-h sampling is about 0.5 nmole m−3 (0.01 ppb) for HNO3 and 3 nmole m−3 for particulate NO−3. The sampling equipment is cheap and a relatively cheap ion chromatograph can be constructed according to the description in this article. When ion chromatography is used the ambient SO2 and particulate SO2−4 concentrations will also be obtained.

Measurements of nitrous acid in an urban area

Atmospheric concentrations of nitrous acid were measured during a 5 month period in the city of Gothenburg in Sweden. Samples of HNO2 were collected in 12-h intervals with the sodium carbonate denuder technique. During the period January to May, values in the range of 1–50 nmole m−3 were observed. Simultaneous measurements of NO, NO2 and H2O show that observed night-time HNO2 concentrations are approximately 10–50 % of roughly calculated equilibrium concentrations, while the corresponding ratios during daytime are lower. This indicates that HNO2 is decomposed during daytime. Correlation coefficient calculations indicate that the reaction NO + NO2 + H2O → 2HNO2 is a major dark source of nitrous acid in urban air.

Effects of air pollution on materials and cultural heritage: ICP materials celebrates 25 years of research

An overview is given of all results from the International Co-operative Programme on Effects on Materials including Historic and Cultural Monuments (ICP Materials), which was launched in 1985. Since then, about twenty different materials have been exposed repeatedly in a network of test sites consisting of more than twenty sites with an extensive environmental characterisation and more than sixty official reports have been issued. Recent results on trends in corrosion, soiling, and pollution show that corrosion of carbon steel, zinc, and limestone is today substantially lower than 25 years ago, but while corrosion of carbon steel has decreased until today, corrosion of zinc and limestone has remained more or less constant since the turn of the century. Unique data are given on measured HNO3 concentrations from 2002-2003, 2005-2006, and 2008-2009, and the relative average decrease was about the same from 2002-2003 to 2005-2006 as it was from 2005-2006 to 2008-2009.

Observed regional distribution of sulfur dioxide in Asia

SO2 concentrations have been measured for one year at forty-five locations throughout Asia using passive samplers. Duplicate samples were exposed at each site for one month intervals. The sites were selected to provide background information on the distribution of SO2 over wide geographical regions, with emphasis on the regional characteristics around areas estimated to be sensitive to sulfur deposition. The annual mean values ranged from less than 0.3 μg/m3 at Tana Rata, located at 1545 m on the Malaysia Peninsula, Lawa Mandau, (Borneo) Malaysia, and Dhankuta, Nepal, to values greater than 20 μg/m3 at Luchongguan (Guiyang) China, Babar Mahal, Nepal, and Hanoi, Vietnam. In general high concentrations were measured throughout China, with the highest concentrations in the heavy industrial areas in Guiyang. The concentrations in east Asia around the Korea peninsula were ∼5 μg/m3. The concentrations in the southeast Asia tropics were low, with no station in Malaysia and Indonesia having average concentrations exceeding 1.7 μg/m3. The observed SO2 concentrations were found to display a distinct seasonal cycle which is strongly influenced by the seasonality of winds and precipitation patterns.

LONG-RANGE TRANSPORT OF GASEOUS AND PARTICULATE OXIDIZED NITROGEN COMPOUNDS

Measurements of NO 2 , PAN, HNO 3 and particulate NO 3 − as 24-h mean concentration values have been carried out at a clean air station. The station is situated on the Swedish west coast 40 km south of Gothenburg. Measurements from November 1981 to October 1982 are presented. NO 2 was measured with the Saltzman method after removal of ozone and PAN with a gas chromatographic method. HNO 3 was sampled in a denuder and particulate NO 3 − was sampled on an impregnated filter behind the denuder. The denuder and filter were then analysed by ion chromatography. Episodes of high concentrations occurred several times during the year. On these occasions the air was transported over a long range from the continent. 72-h back trajectories are available for this station at 6-h intervals during the whole period of measurements. Monthly mean concentrations of these four species, together with data on SO 2 and particulate sulphate are presented. Analysis of the data as a function of the direction of the back trajectory and correlations between nitrogen and sulphate compounds are also given.