Long-term measurements of aerosol and carbon monoxide at the ZOTTO tall tower to characterize polluted and pristine air in the Siberian taiga

Abstract

Abstract. Siberia is one of few continental regions in the Northern Hemisphere where the atmosphere may sometimes approach pristine background conditions. We present the time series of aerosol and carbon monoxide (CO) measurements between September 2006 and December 2011 at the Zotino Tall Tower Observatory (ZOTTO) in Central Siberia (61 • N; 89 • E). We investigate the seasonal, weekly and diurnal variations of aerosol properties (including absorption and scattering coefficients and derived parameters, such as equivalent black carbon (BC e ), Ångström exponent, single scattering albedo, and backscattering ratio) and the CO mixing ratios. Criteria were established to distinguish polluted from near-pristine air masses, providing quantitative characteristics for each type. Depending on the season, 23-36 % of the sampling time at ZOTTO was found to be representative of a clean atmosphere. The summer pristine data indicate that primary biogenic and secondary organic aerosol formation are quite strong particle sources in the Siberian taiga. The summer seasons 2007-2008 were dominated by an Aitken mode around 80 nm size, whereas the summer 2009 with prevailing easterly winds produced particles in the accumulation mode around 200 nm size. We found these differences to be mainly related to air temperature, through its effect on the production rates of biogenic volatile organic compounds (VOC) precursor gases. In winter, the particle size distribution peaked at 160 nm, and the footprint of clean background air was characteristic for aged particles from anthropogenic sources at great distances from ZOTTO and diluted biofuel burning emissions from domestic heating. The wintertime polluted air originates mainly from large cities south and southwest of the site; these particles have a dominant mode around 100 nm, and the BC e / CO ratio of 7-11 ng m −3 ppb −1 suggests dominant contributions from coal and biofuel burning for heating. During summer, anthropogenic emissions are the dominant contributor to the pollution particles at ZOTTO, while only 12 % of the polluted events are classified as biomass-burning-dominated, but then often associated with extremely high CO concentrations and aerosol absorption coefficients. Two biomass-burning case studies revealed different BC e / CO ratios from different fire types, with the agricultural fires in April 2008 yielding a very high ratio of 21 ng m −3 ppb −1 . Overall, we find that anthropogenic sources dominate the aerosol population at ZOTTO most of the time, even during nominally clean episodes in winter, and that near-pristine conditions are encountered only in the growing season and then only episodically.

Occurrence of pristine aerosol environments on a polluted planet

“…In the NH, prolonged pristine periods generally occur only over continental regions above 60°N, such as in boreal Canada (32) and Russia (33), where aerosol is affected strongly by natural forest fire emissions. Here, CCN concentrations are highly variable, but generally range from 100 to 1,000 cm −3 .…”

Black and brown carbon over central Amazonia: Long-term aerosol measurements at the ATTO site

“…Other remote site observations have found no significant diel variation of the absorption coefficient, due to efficient mixing of the planetary boundary layer (PBL) and low anthropogenic emissions (Chi et al, 2013). However, the high convectivity at tropical latitudes makes possible the entrainment of high altitude air masses that bring regional and/or LRT emissions, as observed before at an Amazonian site during the dry season (Brito et al, 2014).…”

Long-term measurements (2010–2014) of carbonaceous aerosol and carbon monoxide at the Zotino Tall Tower Observatory (ZOTTO) in central Siberia

“…Details about this method and the methodology used for data analysis and interpretation correction can be found in Chi et al (2013). In this study, PSAP and TOT measurements cover the date range from 19 April 2010 to 15 May 2012; therefore, the PSAP data will be mainly used to quantify the correction factor (BC e / EC ratio) between the two methods used.…”

“…With regard to aerosol, a study of the representativeness of the ZOTTO facility and first analyses of the particle size distribution data can be found in Heintzenberg et al (2008) and Heintzenberg and Birmili (2010); a statistical analysis of particle size distribution, particle absorption, and carbon monoxide (CO) data taken from the first 4 years of operation of the ZOTTO facility (September 2006 to January 2010) is given in Heintzenberg et al (2011), together with seasonally dependent major air mass pathways and the related particle size distributions. An extended statistical analysis of aerosol properties including scattering coefficients, Ångström exponents, single scattering albedo, and backscattering ratios, as well as a CO data set with seasonal, weekly, and diurnal variations between September 2006 and December 2011 can be found in Chi et al (2013).…”