Total OH Reactivity Changes Over the Amazon Rainforest During an El Niño Event

Pfannerstill, Eva Y.; Nölscher, A. C.; Yáñez‐Serrano, Ana María; Bourtsoukidis, Efstratios; Keßel, Stephan; Janssen, Ruud H. H.; Tsokankunku, Anywhere; Wolff, Stefan; Sörgel, Matthias; Sá, Marta; Araújo, Alessandro; Walter, David; Lavrič, Jošt V.; Dias-Júnior, Cléo Q.; Kesselmeier, J.; Williams, Jonathan

doi:10.3389/ffgc.2018.00012

Cited by 21 publications

(35 citation statements)

References 116 publications

(169 reference statements)

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“…Data availability. The data used in this study will be available from August 2019 to all scientists agreeing to the AQABA protocol at https://doi.org/10.5281/zenodo.3354117 (Pfannerstill et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

Shipborne measurements of total OH reactivity around the Arabian Peninsula and its role in ozone chemistry

et al. 2019

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Abstract. The Arabian Peninsula is characterized by high and increasing levels of photochemical air pollution. Strong solar irradiation, high temperatures and large anthropogenic emissions of reactive trace gases result in intense photochemical activity, especially during the summer months. However, air chemistry measurements in the region are scarce. In order to assess regional pollution sources and oxidation rates, the first ship-based direct measurements of total OH reactivity were performed in summer 2017 from a vessel traveling around the peninsula during the AQABA (Air Quality and Climate Change in the Arabian Basin) campaign. Total OH reactivity is the total loss frequency of OH radicals due to all reactive compounds present in air and defines the local lifetime of OH, the most important oxidant in the troposphere. During the AQABA campaign, the total OH reactivity ranged from below the detection limit (5.4 s−1) over the northwestern Indian Ocean (Arabian Sea) to a maximum of 32.8±9.6 s−1 over the Arabian Gulf (also known as Persian Gulf) when air originated from large petroleum extraction/processing facilities in Iraq and Kuwait. In the polluted marine regions, OH reactivity was broadly comparable to highly populated urban centers in intensity and composition. The permanent influence of heavy maritime traffic over the seaways of the Red Sea, Gulf of Aden and Gulf of Oman resulted in median OH sinks of 7.9–8.5 s−1. Due to the rapid oxidation of direct volatile organic compound (VOC) emissions, oxygenated volatile organic compounds (OVOCs) were observed to be the main contributor to OH reactivity around the Arabian Peninsula (9 %–35 % by region). Over the Arabian Gulf, alkanes and alkenes from the petroleum extraction and processing industry were an important OH sink with ∼9 % of total OH reactivity each, whereas NOx and aromatic hydrocarbons (∼10 % each) played a larger role in the Suez Canal, which is influenced more by ship traffic and urban emissions. We investigated the number and identity of chemical species necessary to explain the total OH sink. Taking into account ∼100 individually measured chemical species, the observed total OH reactivity can typically be accounted for within the measurement uncertainty (50 %), with 10 dominant trace gases accounting for 20 %–39 % of regional total OH reactivity. The chemical regimes causing the intense ozone pollution around the Arabian Peninsula were investigated using total OH reactivity measurements. Ozone vs. OH reactivity relationships were found to be a useful tool for differentiating between ozone titration in fresh emissions and photochemically aged air masses. Our results show that the ratio of NOx- and VOC-attributed OH reactivity was favorable for ozone formation almost all around the Arabian Peninsula, which is due to NOx and VOCs from ship exhausts and, often, oil/gas production. Therewith, total OH reactivity measurements help to elucidate the chemical processes underlying the extreme tropospheric ozone concentrations observed in summer over the Arabian Basin.

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Section: Discussionmentioning

confidence: 99%

Shipborne measurements of total OH reactivity around the Arabian Peninsula and its role in ozone chemistry

et al. 2019

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“…The regional atmospheric circulation has a seasonal pattern driven by the annual north-south shift of the Intertropical Convergence Zone (ITCZ) over the Atlantic Ocean (Andreae et al, 2012(Andreae et al, , 2015Pöhlker et al, 2019). During the dry season, which we define here from July to October, ATTO is located south of the ITCZ.…”

Section: Site Descriptionmentioning

confidence: 99%

“…Most of the data points in the ESE wind direction match the reference slope for biofuel and tropical forest burning. Both of these are linked to human activity, and according to the comprehensive study by Pöhlker et al (2019) in the ESE direction there is substantial fire activity, the rainforest has suffered more fragmentation and degradation, and there are more settlements. It is worth recalling that here we are focusing on nighttime data when stable atmospheric conditions prevail; therefore, the BC associated with biofuel burning might come from nearby settlements.…”

Section: Rejecting Biomass Burning and The Amazon River As Potential mentioning

confidence: 99%

Understanding nighttime methane signals at the Amazon Tall Tower Observatory (ATTO)

et al. 2020

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Abstract. Methane (CH4) atmospheric mixing ratio measurements are analyzed for the period between June 2013 and November 2018 at the Amazon Tall Tower Observatory (ATTO). We describe the seasonal and diurnal patterns of nighttime events in which CH4 mixing ratios at the uppermost (79 m a.g.l.) inlet are significantly higher than the lowermost inlet (4 m a.g.l.) by 8 ppb or more. These nighttime events were found to be associated with a wind direction originating from the southeast and wind speeds between 2 and 5 m s−1. We found that these events happen under specific nighttime atmospheric conditions when compared to other nights, exhibiting less variable sensible heat flux, low net radiation and a strong thermal stratification above the canopy. Our analysis indicates that even at wind speeds of 5.8 m s−1 the turbulence intensity, given by the standard deviation of the vertical velocity, is suppressed to values lower than 0.3 m s−1. Given these findings, we suggest that these nighttime CH4 enhancements are advected from their source location by horizontal nonturbulent motions. The most likely source location is the Uatumã River, possibly influenced by dead stands of flooded forest trees that may be enhancing CH4 emissions from those areas. Finally, biomass burning and the Amazon River were discarded as potential CH4 sources.

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“…An NO/NO2 correction was not performed due to the low NOx levels at the site (Pfannerstill et al, 2018;Wolff, 2015) with maximum NO and NO2 mixing ratios of 0.36 ppb and 0.62 ppb in the dry season (October 2018), respectively. The correction for pseudo-1st-order deviation was derived from tests using propene, isoprene and propane, resulting in a weighted correction factor in dependence of alkene fraction in calculated OH reactivity and pyrrole/OH ratio (Eq.…”

Section: Total Oh Reactivity Data Analysismentioning

confidence: 99%

Total OH reactivity over the Amazon rainforest: variability with temperature, wind, rain, altitude, time of day, season, and an overall budget closure

Pfannerstill¹,

Reijrink²,

Edtbauer³

et al. 2020

Preprint

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Abstract. The tropical forests are Earth’s largest source of biogenic volatile organic compounds (BVOCs) and thus also the largest atmospheric sink region for the hydroxyl radical (OH). However, the OH sink above tropical forests is poorly understood, as past studies revealed large unattributed fractions of total OH reactivity. We present the first total OH reactivity and VOC measurements made at the Amazon Tall Tower Observatory (ATTO) at 80, 150, and 320 m above ground level, covering two dry seasons, one wet and one transition season in 2018–2019. By considering a wide range of previously unaccounted for VOCs, which we identified by PTR-ToF-MS, the unattributed fraction was with an overall average of 19 % within the measurement uncertainty of ~ 35 %. In terms of seasonal average OH reactivity, isoprene accounted for 23–43 % of the total, oxygenated VOCs (OVOCs) for 22–40 %, while monoterpenes, sesquiterpenes, and green leaf volatiles combined were responsible for 9–14 %. These findings show that OVOCs were until now an underestimated contributor to the OH sink above the Amazon forest. By day, total OH reactivity decreased towards higher altitudes with strongest vertical gradients observed around noon during the dry season (−0.026 s−1 m−1), while the gradient was inverted at night. Seasonal differences in total OH reactivity were observed, with the lowest daytime average and standard deviation of 19.9 ± 6.2 s−1 during a wet–dry transition season with frequent precipitation, 23.7 ± 6.5 s−1 during the wet season, and the highest average OH reactivities during two dry season observation periods with 28.1 ± 7.9 s−1 and 29.1 ± 10.8 s−1, respectively. The effects of different environmental parameters on the OH sink were investigated, and quantified, where possible. Precipitation caused short-term spikes in total OH reactivity, which were followed by below-normal OH reactivity for several hours. Biomass burning increased total OH reactivity by 2.7 s−1 to 9.5 s−1. We present a temperature-dependent parameterization of OH reactivity that could be applied in future models of the OH sink to further reduce our knowledge gaps in tropical forest OH chemistry.

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Total OH Reactivity Changes Over the Amazon Rainforest During an El Niño Event

Cited by 21 publications

References 116 publications

Shipborne measurements of total OH reactivity around the Arabian Peninsula and its role in ozone chemistry

Shipborne measurements of total OH reactivity around the Arabian Peninsula and its role in ozone chemistry

Understanding nighttime methane signals at the Amazon Tall Tower Observatory (ATTO)

Total OH reactivity over the Amazon rainforest: variability with temperature, wind, rain, altitude, time of day, season, and an overall budget closure

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