Biomass burning emission disturbances of isoprene oxidation in a tropical forest

Abstract

Abstract. We present a characterization of the chemical composition of the atmosphere of the Brazilian Amazon rainforest based on trace gas measurements carried out during the South AMerican Biomass Burning Analysis (SAMBBA) airborne experiment in September 2012. We analyzed the observations of primary biomass burning emission tracers, i.e., carbon monoxide (CO), nitrogen oxides (NOx), ozone (O3), isoprene, and its main oxidation products, methyl vinyl ketone (MVK), methacrolein (MACR), and isoprene hydroxy hydroperoxide (ISOPOOH). The focus of SAMBBA was primarily on biomass burning emissions, but there were also several flights in areas of the Amazon forest not directly affected by biomass burning, revealing a background with a signature of biomass burning in the chemical composition due to long-range transport of biomass burning tracers from both Africa and the eastern part of Amazonia. We used the [MVK + MACR + ISOPOOH] ∕ [isoprene] ratio and the hydroxyl radical (OH) indirect calculation to assess the oxidative capacity of the Amazon forest atmosphere. We compared the background regions (CO < 150 ppbv), fresh and aged smoke plumes classified according to their photochemical age ([O3] ∕ [CO]), to evaluate the impact of biomass burning emissions on the oxidative capacity of the Amazon forest atmosphere. We observed that biomass burning emissions disturb the isoprene oxidation reactions, especially for fresh plumes ([MVK + MACR + ISOPOOH] ∕ [isoprene] = 7) downwind. The oxidation of isoprene is higher in fresh smoke plumes at lower altitudes (∼ 500 m) than in aged smoke plumes, anticipating near the surface a complex chain of oxidation reactions which may be related to secondary organic aerosol (SOA) formation. We proposed a refinement of the OH calculation based on the sequential reaction model, which considers vertical and horizontal transport for both biomass burning regimes and background environment. Our approach for the [OH] estimation resulted in values on the same order of magnitude of a recent observation in the Amazon rainforest [OH] ≅ 106 (molecules cm−3). During the fresh plume regime, the vertical profile of [OH] and the [MVK + MACR + ISOPOOH] ∕ [isoprene] ratio showed evidence of an increase in the oxidizing power in the transition from planetary boundary layer to cloud layer (1000–1500 m). These high values of [OH] (1.5 × 106 molecules cm−3) and [MVK + MACR + ISOPOOH] ∕ [isoprene] (7.5) indicate a significant change above and inside the cloud decks due to cloud edge effects on photolysis rates, which have a major impact on OH production rates.

Fine particle characterization in a coastal city in China: composition, sources, and impacts of industrial emissions

“…Although the SSP emits much less ammonium sulfate particles, and gaseous CO and NO x , we found that the ratios of NO x /SO 2 and NO x /CO were similar between these two steel plants. The previously reported values of NO x /CO from other emission sources, e.g., biomass burning (0.056-8.33) and on-road motor vehicles (0.04-0.05), were significantly larger than the NO x /CO ratio during steel plant plumes in this study (Schürmann et al, 2007;Fujita et al, 2012;Tiwari et al, 2015;Santos et al, 2018). Moreover, the NO x /CO ratio during plume-excluded period was close to the values from vehicle emissions (0.04 vs. 0.04-0.05) (Fujita et al, 2012).…”

Sources and processes that control the submicron organic aerosol composition in an urban Mediterranean environment (Athens): a high temporal-resolution chemical composition measurement study

“…For the PILS, the detection limit was calculated at 1 ppb for Na + and NH + 4 and 2 ppb for K + . Non-sea-salt K + (nss-K + ) concentrations were calculated using the Na + concentrations and the Na + /K + ratio in seawater as a reference (Sciare et al, 2005). The concentrations reported were blank corrected.…”

Low-level summertime isoprene observed at a forested mountaintop site in southern China: implications for strong regional atmospheric oxidative capacity

“…Since the OH and NO 3 concentrations were not measured in this campaign, they were estimated by using a photochemical box model incorporating the master chemical mechanism (PBM-MCM). MCM (v3.2) has a good performance on calculating free radicals and intermediate products (Jenkin et al, 1997Saunders et al, 2003), as it adopts a nearexplicit mechanism, involving 5900 chemical species and around 16 500 reactions. In this study, the observed hourly data of air pollutants (O 3 , NO, NO 2 , CO, SO 2 and VOCs) and meteorological parameters (temperature and relative humidity) for the sampling period were input into the model for simulations.…”

“…Ambient measurements in pristine Amazon forests demonstrated that high OH concentrations often occur under high-isoprene and low-NO x (< 1 ppbv) conditions where OH regeneration contributes greatly to the oxidative capacity of the atmosphere (Lelieveld et al, 2008;Fuchs et al, 2013;Rohrer et al, 2014). Several recent studies have shown that small increases of NO x concentration above the background level can lead to a large change in the oxidative capacity and chemistry of the forest atmosphere (Liu et al, 2016(Liu et al, , 2018Su et al, 2016;Santos et al, 2018). In addition, the high OH-recycling efficiency is not unique to pristine forests; an important but different OH-recycling mechanism has been discovered in an isoprene-emitting forest suffering from heavy air pollution (Hofzumahaus et al, 2009).…”

“…The sum of MVK and MACR accounts for about 80 % of the carbon in the initial stage of isoprene oxidation in the atmosphere (Jenkin et al, 2015). Field measurements of MVK and MACR have been widely conducted during the past decades to explore the oxidation mechanisms of isoprene in forested environments (Stroud et al, 2001;Apel et al, 2002;Kuhn et al, 2007;Kalogridis et al, 2014;Liu et al, 2016Liu et al, , 2018Santos et al, 2018). Few studies, however, have been performed at high-altitude mountain sites to investigate the influence of anthropogenic emissions to the isoprene oxidation and to evaluate the regional AOC (Reissell and Arey, 2001;Dreyfus et al, 2002;Guo et al, 2012).…”