Mass balance of the atmospheric aerosol in a South African subtropical savanna (Nylsvley, May 1997)

Abstract

(CI-, NO•-, SO42-, oxalate, NH•-, Na +, K +, Ca 2+, Mg2+), trace metals and crustal elements (Fe, Mn, Ca, Mg, Pb, Cu, Ag, Cd), "black carbon" (BC), total carbon (TC); and in selected samples for aerosol humidity, for mono-and dicarboxylic acids and other polar organic components, and for cellulose as a tracer for plant debris. Aerosol mass balances for the individual samples were constructed from the sum of following groups: Humidity (determined as weight loss at 100øC with a microthermobalance), ammonium sulfate, C1-and NOj, organic material, BC, and soil dust. On the average, the fit between the sum of the determined groups of components and the gravimetrically determined mass was within 6%, whereas deviations ranged for individual samples from -12 to +27% relative to the gravimetrically determined mass. The main component in aerosol was soil dust (36%), followed by organic material (28%), and ammonium sulfate (27%). Humidity was 6%, BC was 2%, and C1-and NOj were i% of aerosol mass. The low BC/TC ratio of 0.09 indicated little influence from combustion sources. The diurnal trend of the BC/TC ratio of 0.06 during day and 0.14 during night indicated a daytime source for organic components with no BC associated. As there were no industrial or other anthropogenic sources evident, the daytime source of organic components is assumed to be gas-particle conversion from biogenic emissions. Plant debris and organic acids were the major analytically accessible groups; however, together they form only 7.2% of the carbonaceous material. With 0.4% other polar organics and 5.7% BC in this group, 86.7% of the carbonaceous material remains unidentified. In this work we present a detailed mass balance of the atmospheric aerosol of a biogenically dominated southern African site for "nonburning" conditions. The balance includes organic and elemental carbon as well as aerosol humidity. In addition to ion and elemental analysis, we apply a combination of thermal methods originally proposed by Puxbaum [1979a, 1979b]

Chemical Compounds in the Atmosphere

“…The major part of the TSP is formed by electrolytes (Na + , K + , NH þ 4 , Cl À , NO À 3 , SO 2À 4 ) (25 -35%), carbonaceous material (8 -11%), and mineralic components (Ca, Mg, Si, Al compounds) (16 -18%). Similar results were found for aerosols collected at a background site in the South African savanna (Puxbaum et al 2000).…”

Gas to particle distribution of low molecular weight dicarboxylic acids at two different sites in central Europe (Austria)

“…The water soluble fraction contributes to cloud condensation nuclei (CCN) concentrations (Novakov & Penner, 1993). An important group of water soluble organic compounds in the atmospheric aerosol are dicarboxylic acids, which on average account for 0.5-3% of the total particulate carbon in urban and rural environment, and close to or above 10% in remote continental or marine areas (Sempere & Kawamura, 1994;Khwaja, 1995;Puxbaum, Rendl, Allbashi, Otter, & Scholes, 2000;Wang & Shooter, 2004). Generally the predominance of oxalic acid, followed by malonic acid and succinic acid was shown for aerosols from distinctly different sites (Kawamura & Ikushima, 1993;Kawamura, Sempere, & Imai, 1996;Limbeck & Puxbaum, 1999a;Wang, Niu, Liu, & Wang, 2002).…”

The SOA/VOC/NO<sub>x</sub> system: an explicit model of secondary organic aerosol formation

“…Their low atmospheric concentrations cause analytical difficulties (e.g., Jacobson et al, 2000;Turpin et al, 2000;Kanakidou et al, 2005). During in situ measurement campaigns, less than 20% of the total particulate organic mass is typically identified (Rogge et al, 1993;Puxbaum et al, 2000). Moreover major difficulties hinder the simulation of SOA formation on the basis of first principles.…”