Changes to the chemical state of the Northern Hemisphere atmosphere during the second half of the twentieth century

Abstract

Abstract. The NO x (NO and NO 2 ) and HO x (OH and HO 2 ) budgets of the atmosphere exert a major influence on atmospheric composition, controlling removal of primary pollutants and formation of a wide range of secondary products, including ozone, that can influence human health and climate. However, there remain large uncertainties in the changes to these budgets over recent decades. Due to their short atmospheric lifetimes, NO x and HO x are highly variable in space and time, and so the measurements of these species are of limited value for examining long-term, largescale changes to their budgets. Here, we take an alternative approach by examining long-term atmospheric trends of alkyl nitrates, the production efficiency of which is dependent on the atmospheric [NO] / [HO 2 ] ratio. We derive long-term trends in the alkyl nitrates from measurements in firn air from the NEEM site, Greenland. Their mixing ratios increased by a factor of 3-5 between the 1970s and 1990s. This was followed by a steep decline to the sampling date of 2008. Moreover, we examine how the trends in the alkyl nitrates compare to similarly derived trends in their parent alkanes (i.e. the alkanes which, when oxidised in the presence of NO x , lead to the formation of the alkyl nitrates). The ratios of the alkyl nitrates to their parent alkanes increased from around 1970 to the late 1990s. This is consistent with large changes to the [NO] / [HO 2 ] ratio in the Northern Hemisphere atmosphere during this period. Alternatively, they could represent changes to concentrations of the hydroxyl radical, OH, or to the transport time of the air masses from source regions to the Arctic.

Occurrence of Volatile and Semi-Volatile Organic Pollutants in the Russian Arctic Atmosphere: The International Siberian Shelf Study Expedition (ISSS-2020)

“…Nevertheless, the currently available literature data on the chemical composition and levels of atmospheric pollutants at high latitudes are notably incomplete. Most of the earlier studies were focused mainly on the determination of the major gaseous pollutants (nitrogen and sulfur oxides, carbon monoxide and dioxide, ozone, methane), particulate matter, and black carbon, present in relatively high levels and being of paramount importance from the climatology point of view [13,14]. Within the framework of the international project "Arctic Monitoring and Assessment Program (AMAP)" [15] persistent organic pollutants (POP) and chemicals of emerging Arctic concern (CEAC) [16] as the most dangerous micropollutants have been monitored in the Arctic environment for many years.…”