Periodic Reporting for period 2 - SAPIENTIAM (Secondary organic Aerosols Production in pre and post-Industrial-like ENvironments : The Impact of biogenic and Anthropogenic emissions on cliMate)
Periodo di rendicontazione: 2021-03-01 al 2022-02-28
The main scope of the SAPIENTIAM (Secondary organic Aerosols Production in pre-and post-Industrial-like ENvironments: The Impact of biogenic and Anthropogenic emissions on climate) project is the identification of innovative mechanisms to describe and investigate the atmospheric composition in pristine environment that are affected by the anthropogenic emissions. The latter, such as nitrogen oxides (NOx, e.g NO and NO2), are related to human activities in post-industrial scenarios. In detail, the project studies the effect of NOx emissions on Secondary Organic Aerosol (SOA) formation and its chemical compositions. Moreover, we investigate the production and the gas to particle partitioning of organonitrates (ONs, e.g. ΣRO2NO2, and ΣRONO2). Despite the SOA yield as a function of different NOx regimes have been investigated in previous studies, further laboratory experiments are necessary, as the dependency is not univocally determined, to explore the chemistry in chamber conditions that represent more realistically atmospheric concentrations. Particulate matters, which can be emitted both by anthropogenic and biogenic activities, play a significant role in the radiative forcing, i.e. on climate change, via direct and indirect effects; they affect also the atmospheric visibility, and their adverse impact on human health has been demonstrated. At the same time, the ONs represent reservoir species for NO2, and the reaction cycle for their reaction strongly affects the tropospheric ozone (O3) production, which is a greenhouse gas with important oxidative capacity. As a consequence, the study of SOA and ONs production in different NOx regimes has important, different effects in terms of both climate change and air quality, with interdisciplinary impact on society in terms of policy and economy.
The SAPIENTIAM project allowed to produce more and innovative knowledge about the role played by the ONs in SOA formation, chemical composition and yield. The gas-to-particle partition of ONs it seems to be really important in new particle formation events and the chamber experiments results have positive feedback in field campaigns data analysis and help to their interpretation.
The SAPIENTIAM project allowed to produce more and innovative knowledge about the role played by the ONs in SOA formation, chemical composition and yield. The gas-to-particle partition of ONs it seems to be really important in new particle formation events and the chamber experiments results have positive feedback in field campaigns data analysis and help to their interpretation.
The preliminary research activities started working on chamber experiment plans and the TD-LIF installation with the Harvard Environmental Chamber (HEC). After the HEC laboratory settings and the preliminary tests were completed, we performed seven experiments varying the NOx concentration in the chamber starting from a background level (<0.3 ppb) up to 24 ppb of initial NOx, descriptive of an urban environment. Analyzing the data collected during the chamber experiments, we have been able to identify a new threshold level between the “clear” and “polluted” regimes of NOx affecting the SOA formation. Moreover, we have been able to measure both the gas and particle phase of the organonitrates (gONs and pONs, respectively) in chamber experiments, producing also the relative speciation (differentiating between alkylnitrates and peroxynitrates). This is a significant improvement in the knowledge about the pONs contribution to the total SOA. We found that, for 1 to 6 ppb NOx, the yield of SOA particle mass concentration increased from 0.02 to 0.044 with NOx concentration. For >6 ppb NOx, the yield steadily dropped, reaching 0.034 at 24 ppb NOx. By comparison, the yield of pONs steadily increased from 0.002 to 0.022 across the range of investigated NOx concentrations. The yield of gONs likewise increased from 0.005 to 0.148. Moreover, we found that the gas-to-particle partitioning ratio (pONs/(pONs+gONs)) depended strongly on the NOx concentration, changing from 0.27 to 0.13 as the NOx increased from <1 to 24 ppb. In the atmosphere, there is typically a crossover point between clean and polluted conditions that strongly affects SOA production, and the results herein quantitatively identify 6 ppb NOx as that point for α-pinene photo-oxidation under this study conditions, including production and partitioning of organonitrates. We suggested that the trends in SOA yield and partitioning ratio as a function of NOx occur because of changes in pONs volatility. More experiments are needed to investigate the role played by the relative humidity and to measure, by using the CIMS technique, the molecular composition of the produced SOA and pONs. The results we found have been published, and the manuscript can be found at the following link: https://pubs.acs.org/doi/10.1021/acs.est.1c08380(si apre in una nuova finestra).
To test the chamber results respect what has been found in real atmosphere, we analyzed the data collected during two field campaigns: the GoAmazon and the APHH-Beijing campaigns. Next to the data analysis, by using custom code based on MatLab, we applied a 0D box model based on the Master Chemical Mechanism (MCM) (F0AM model). Preliminarily, we did several model test to be able to properly reproduce both the O3 and the ONs concentrations with the model. In details, we had to optimize the dilution term introducing and correctly parametrizing also the organonitrates deposition: this requested a deep analysis of the model principle of working and literature studies to introduce these terms in the F0AM model. Studying the Amazon chemistry, we found that high concentrations of NOx (NOx = NO + NO2) have been recorded in the dry season in Amazonas during the GoAmazon2014/15 international experiments. We investigated the ozone (O3) and ONs productions by the Master Chemical Mechanism (MCM). The model allows to reproduce the O3 and the ONs with correlation coefficients of ̴0.88 and ̴0.43 respectively. We identified two different regimes in the ozone production budget and we have been able to model the ONs speciation, recognizing its diurnal pattern. The results have not been published yet, but we are working on the draft of the manuscript.
From the analysis of the Beijing data, we identified three different scenarios, identifiable also looking at the different air masses direction: 1) low NOx regime; 2) high NOx regime, and 3) mixed air masses regime. We focused on the study of the formation pathways of organonitrates (ONs) from NOx and the implications for SOA and O3 production under these three different meteorological scenarios. We identified a really interesting mechanism of ONs gas-to-particle partitioning and new particle formation events in Beijing. The results have not been published yet, further and more detailed findings will be soon available in a manuscript.
To test the chamber results respect what has been found in real atmosphere, we analyzed the data collected during two field campaigns: the GoAmazon and the APHH-Beijing campaigns. Next to the data analysis, by using custom code based on MatLab, we applied a 0D box model based on the Master Chemical Mechanism (MCM) (F0AM model). Preliminarily, we did several model test to be able to properly reproduce both the O3 and the ONs concentrations with the model. In details, we had to optimize the dilution term introducing and correctly parametrizing also the organonitrates deposition: this requested a deep analysis of the model principle of working and literature studies to introduce these terms in the F0AM model. Studying the Amazon chemistry, we found that high concentrations of NOx (NOx = NO + NO2) have been recorded in the dry season in Amazonas during the GoAmazon2014/15 international experiments. We investigated the ozone (O3) and ONs productions by the Master Chemical Mechanism (MCM). The model allows to reproduce the O3 and the ONs with correlation coefficients of ̴0.88 and ̴0.43 respectively. We identified two different regimes in the ozone production budget and we have been able to model the ONs speciation, recognizing its diurnal pattern. The results have not been published yet, but we are working on the draft of the manuscript.
From the analysis of the Beijing data, we identified three different scenarios, identifiable also looking at the different air masses direction: 1) low NOx regime; 2) high NOx regime, and 3) mixed air masses regime. We focused on the study of the formation pathways of organonitrates (ONs) from NOx and the implications for SOA and O3 production under these three different meteorological scenarios. We identified a really interesting mechanism of ONs gas-to-particle partitioning and new particle formation events in Beijing. The results have not been published yet, further and more detailed findings will be soon available in a manuscript.
Compare to previous analogues studies, the new settings chosen for chamber experiments during the SAPIENTIAM project allow to simulate more realistic levels of species in the HEC chamber (in terms of VOC, oxidants, ozone, and NOx) with a successful production of secondary organic matter. Moreover, the use of TD-LIF is quite innovative and was successfully integrated with the HEC setup, allowing to measure the gas-to-particle partitioning and speciation of the organonitrates. The SAPIENTIAM project allowed to identify a new threshold between "clean" and "polluted" condiions for the SOA yield and to study the effect of anthropogenic emissions (NOx) in different environments (Amazon forest and Beijing megacity).