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Long-term measurements of atmospheric mass concentrations of black carbon (BC) are needed to investigate changes in its emission, transport, and deposition. However, depending on instrumentation, parameters related to BC such as aerosol absorption coefficient (babs) have been measured instead. Most ground-based measurements of babs in the Arctic have been made by filter-based absorption photometers, including particle soot absorption photometers (PSAP), continuous light absorption photometer (CLAP), Aethalometers, and multi-angle absorption photometers (MAAP). The measured babs can be converted to mass concentrations of BC (MBC) by assuming the value of the mass absorption cross section (MAC; MBC = babs/MAC). However, the accuracy of conversion of babs to MBC has not been adequately assessed. Here, we introduce a systematic method for deriving MAC values from babs measured by these instruments and independently measured MBC. In this method, MBC was measured with a filter-based absorption photometer with a heated inlet (COSMOS). COSMOS-derived MBC (MBC (COSMOS)) is traceable to a rigorously calibrated single particle soot photometer (SP2) and the absolute accuracy of MBC (COSMOS) has been demonstrated previously to be about 15 % in Asia and the Arctic. The necessary conditions for application of this method are a high correlation of the measured babs with independently measured MBC, and long-term stability of the regression slope, which is denoted as MACcor (MAC derived from the correlation). In general, babs–MBC (COSMOS) correlations were high (r2 = 0.76–0.95 for hourly data) at Alert in Canada, Ny-Ålesund in Svalbard, Barrow in Alaska, Pallastunturi in Finland, and Fukue in Japan, and stable for up to 10 years. We successfully estimated MACcor values (10.6–15.2 m2 g−1 at a wavelength of 550 nm) for these instruments and these MACcor values can be used to obtain error-constrained estimates of MBC from babs measured at these sites even in the past, when COSMOS measurements were not made. Because the absolute values of MBC in these Arctic sites estimated by this method are consistent with each other, they are applicable to the study of spatial and temporal variation of MBC in the Arctic and to evaluation of the performance of numerical model calculations.

We investigated atmospheric new particle formation (NPF) in the Amazon rainforest using direct measurement methods. To our knowledge this is the first direct observation of NPF events in the Amazon region. However, previous observations elsewhere in Brazil showed the occurrence of nucleation-mode particles. Our measurements covered two field sites and both the wet and dry season. We measured the variability of air ion concentrations (0.8–12 nm) with an ion spectrometer between September 2011 and January 2014 at a rainforest site (T0t). Between February and October 2014, the same measurements were performed at a grassland pasture site (T3) as part of the GoAmazon 2014/5 experiment, with two intensive operating periods (IOP1 and IOP2 during the wet and the dry season, respectively). The GoAmazon 2014/5 experiment was designed to study the influence of anthropogenic emissions on the changing climate in the Amazon region. The experiment included basic aerosol and trace gas measurements at the ground, remote sensing instrumentation, and two aircraft-based measurements. The results presented in this work are from measurements performed at ground level at both sites. The site inside the rainforest (T0t) is located 60 km NNW of Manaus and influenced by pollution about once per week. The pasture (T3) site is located 70 km downwind from Manaus and influenced by the Manaus pollution plume typically once per day or every second day, especially in the afternoon. No NPF events were observed inside the rainforest (site T0t) at ground level during the measurement period. However, rain-induced ion and particle bursts (hereafter, “rain events”) occurred frequently (643 of 1031 days) at both sites during the wet and dry season, being most frequent during the wet season. During the rain events, the ion concentrations in three size ranges (0.8–2, 2–4, and 4–12 nm) increased up to about 104–105 cm−3. This effect was most pronounced in the intermediate and large size ranges, for which the background ion concentrations were about 10–15 cm−3 compared with 700 cm−3 for the cluster ion background. We observed eight NPF events at the pasture site during the wet season. We calculated the growth rates and formation rates of neutral particles and ions for the size ranges 2–3 and 3–7 nm using the ion spectrometer data. The observed median growth rates were 0.8 and 1.6 nm h−1 for 2–3 nm sized ions and particles, respectively, with larger growth rates (13.3 and 7.9 nm h−1) in the 3–7 nm size range. The measured nucleation rates were of the order of 0.2 cm−3 s−1 for particles and 4–9×10-3 cm−3 s−1 for ions. There was no clear difference in the sulfuric acid concentrations between the NPF event days and nonevent days (∼9×105 cm−3). The two major differences between the NPF days and nonevent days were a factor of 1.8 lower condensation sink on NPF event days (1.8×10-3 s−1) compared to nonevents (3.2×10-3 s−1) and different air mass origins. To our knowledge, this is the first time that results from ground-based sub-3 nm aerosol particle measurements have been obtained from the Amazon rainforest.