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Anthropogenic emissions of carbon dioxide (CO2) and methane (CH4) in the atmosphere constitute an important component of the related carbon budget. The main source of anthropogenic CO2 is burning of fossil fuels, especially in densely populated areas. Similar emissions of CH4 are associated with the agricultural sector, coal mining, and other human activities, such as waste management and storage and natural gas networks supplying methane to large urban, industrial centers. We discuss several methods aimed at characterizing and quantifying atmospheric loads and fluxes of CO2 and CH4 in Krakow, the second largest city in Poland. The methods are based on atmospheric observations of mixing ratios as well as isotopic composition of the investigated gases. Atmospheric mixing ratios of CO2 and CH4 were measured using gas chromatography (GC) and cavity ring-down spectroscopy (CRDS). The isotopic composition of CO2 and CH4 was analyzed using isotope ratio mass spectrometry (IRMS), accelerator mass spectrometry (AMS), and CRDS techniques. These data, combined with auxiliary information characterizing the intensity of vertical mixing in the lower atmosphere (height of the nocturnal boundary layer [NBL] and atmospheric 222Rn concentration), were further used to quantify emission rates of CO2 and CH4 in the urban atmosphere of Krakow. These methods provide an efficient way of quantifying surface emissions of major greenhouse gases originating from distributed sources, thus complementing the widely used bottom-up methodology based on emission statistics.

THE various reservoirs of the global carbon cycle, with their very different residence times, are linked by a complex and evolving system of exchanges for which natural radiocarbon is the most robust tracer1. Any change in the sizes of these reservoirs, or the exchange rates between them, could perturb the 14C/12C ratio of each other reservoir, and the smallest of them—the atmosphere— would be the most sensitive. In particular, high-resolution reconstructions of past atmospheric 14C/12C ratios may provide important clues to the mechanisms of abrupt climate change. Annually laminated lake sediments potentially provide an optimal record in this respect, as they preserve information about both past atmospheric 14C levels and climate changes, providing absolutely dated material beyond the range of tree-ring chronologies and, unlike corals, directly monitor 14C concentrations in atmospheric CO2. Here we report the relationship between atmospheric 14C concentration and climate changes during the Younger Dryas and early Holocene periods, derived from analyses of the annually laminated sediments of Lake Gśoscia¸azz, in central Poland. We find that atmospheric 14C concentrations during the Younger Dryas were abnormally high, which we interpret as a reduced ventilation rate of the deep ocean, most probably as a result of a decrease in intensity of the North Atlantic Deep Water formation.