Charbel Afif

Detection of Golden apples’ climacteric peak by laser biospeckle measurements

In this paper, we report a study in which a laser biospeckle technique is used to detect the climacteric peak indicating the optimal ripeness of fruits. We monitor two batches of harvested Golden apples going through the ripening phase in low- and room-temperature environments, determine speckle parameters, and measure the emitted ethylene concentration using gas chromatography as reference method. Speckle results are then correlated to the emitted ethylene concentration by a principal component analysis. From a practical point of view, this approach allows us to validate biospeckle as a noninvasive and alternative method to respiration rate and ethylene production for climacteric peak detection as a ripening index.

Speciation of non-methane hydrocarbons (NMHCs) from anthropogenic sources in Beirut, Lebanon

The chemical composition of emissions from the different anthropogenic sources of non-methane hydrocarbons (NMHC) is essential for modeling and source apportionment studies. The speciated profiles of major NMHC sources in Lebanon, including road transport, gasoline vapor, power generation, and solvent use were established. Field sampling have been carried out by canisters in 2012. Around 67 NMHC (C2 to C9) were identified and quantified by using a gas chromatograph equipped with a flame ionization detector. Typical features of the roadway emissions included high percentages of isopentane, butane, toluene, xylenes, ethylene, and ethyne. Gasoline evaporation profiles included high percentage of the C4–C5 saturated hydrocarbons reaching 59xa0%. The main compounds of the power generator emissions are related to combustion. Toluene and C8–C9 aromatics were the most abundant species in emissions from paint applications. Finally, the impact of the use of region-specific source profile is tackled regarding the implication on air quality.

Identification of the major HOx radical pathways in an indoor air environment.

OH and HO2 profiles measured in a real environment have been compared to the results of the INCA-Indoor model to improve our understanding of indoor chemistry. Significant levels of both radicals have been measured and their profiles display similar diurnal behavior, reaching peak concentrations during direct sunlight (up to 1.6×106 and 4.0×107 xa0cm-3 for OH and HO2 , respectively). Concentrations of O3 , NOx , volatile organic compounds (VOCs), HONO, and photolysis frequencies were constrained to the observed values. The HOx profiles are well simulated in terms of variation for both species (Pearsons coefficients: pOH =0.55, pHO2 =0.76) and concentration for OH (mean normalized bias error: MNBEOH =-30%), HO2 concentration being always underestimated (MNBEHO2 =-62%). Production and loss pathways analysis confirmed HONO photolysis role as an OH precursor (here up to 50% of the production rate). HO2 formation is linked to OH-initiated VOC oxidation. A sensitivity analysis was conducted by varying HONO, VOCs, and NO concentrations. OH, HO2 , and formaldehyde concentrations increase with HONO concentrations; OH and formaldehyde concentrations are weakly dependent on NO, whereas HO2 concentrations are strongly reduced with increasing NO. Increasing VOC concentrations decreases OH by consumption and enhances HO2 and formaldehyde.

NitroMAC: An instrument for the measurement of HONO and intercomparison with a long-path absorption photometer

NitroMAC (French acronym for continuous atmospheric measurements of nitrogenous compounds) is an instrument which has been developed for the semi-continuous measurement of atmospheric nitrous acid (HONO). This instrument relies on wet chemical sampling and detection using high performance liquid chromatography (HPLC)-visible absorption at 540 nm. Sampling proceeds by dissolution of gaseous HONO in a phosphate buffer solution followed by derivatization with sulfanilamide/N-(1-naphthyl)-ethylenediamine. The performance of this instrument was found to be as follows: a detection limit of around 3 ppt with measurement uncertainty of 10% over an analysis time of 10 min. Intercomparison was made between the instrument and a long-path absorption photometer (LOPAP) during two experiments in different environments. First, air was sampled in a smog chamber with concentrations up to 18 ppb of nitrous acid. NitroMAC and LOPAP measurements showed very good agreement. Then, in a second experiment, ambient air with HONO concentrations below 250 ppt was sampled. While NitroMAC showed its capability of measuring HONO in moderate and highly polluted environments, the intercomparison results in ambient air highlighted that corrections must be made for minor interferences when low concentrations are measured.

Assessment of indoor HONO formation mechanisms based on in situ measurements and modeling

The photolysis of HONO has been found to be the oxidation driver through OH formation in the indoor air measurement campaign SURFin, an extensive campaign carried out in July 2012 in a classroom in Marseille. In this study, the INCA-Indoor model is used to evaluate different HONO formation mechanisms that have been used previously in indoor air quality models. In order to avoid biases in the results due to the uncertainty in rate constants, those parameters were adjusted to fit one representative day of the SURFin campaign. Then, the mechanisms have been tested with the optimized parameters against other experiments carried out during the SURFin campaign. Based on the observations and these findings, we propose a new mechanism incorporating sorption of NO2 onto surfaces with possible saturation of these surfaces. This mechanism is able to better reproduce the experimental profiles over a large range of conditions.

Assessment of source contributions to air pollution in Beirut, Lebanon: a comparison of source-based and tracer-based modeling approaches

A chemical-transport model (CTM), Polyphemus/Polair3D, is used to investigate the contributions of various anthropogenic and biogenic sources to total organic carbon (OC) in PM2.5 in Beirut, Lebanon, during the summer of 2011. Those results are compared to a tracer-based source apportionment of OC at an ambient site in Beirut where a measurement campaign was conducted in July 2011. The results obtained from the CTM in the base simulation S1 suggest contributions to total simulated OC mass (3.24xa0μg/m3) of 66xa0% (2.14u2009±u20091.07xa0μg/m3) from fossil fuel burning (FFB) and 8xa0% (0.27u2009±u20090.135xa0μg/m3) from biogenic secondary organic carbon (BSOC). The tracer-based approach leads to contribution estimates to total measured OC mass (5.6xa0μg/m3) of 16xa0% (0.9xa0μg/m3u2009±u20090.22) from FFB, 53xa0% (2.9u2009±u20091.7xa0μg/m3) from BSOC, and 32xa0% (1.8u2009±u20090.88xa0μg/m3) from cooking activities. In a second CTM simulation S2, emissions related to cooking activities were added to the emission inventory, monoterpene and sesquiterpene secondary organic aerosol (SOA) surrogate species were added to the boundary conditions, and a lower ratio of semi-volatile organic compounds to primary organic aerosols (SVOC/POA) was used. The S2 results obtained showed contributions to total simulated OC mass (3.01xa0μg/m3) of 33xa0% (0.98u2009±u20090.49xa0μg/m3) from FFB, 18xa0% (0.53u2009±u20090.27xa0μg/m3) from BSOC, and 39xa0% (1.2u2009±u20090.6xa0μg/m3) from cooking activities. The differences between these two methods are discussed in terms of their uncertainties and biases. The comparison of both approaches showed that the model underestimates the secondary fraction of OC, which may be due to underestimations of some biogenic volatile organic compound (VOC) emissions and/or boundary concentrations as well as the use of SOA yields that may not be representative of the eastern Mediterranean region. Concerning the tracer-based approach, the use of tracer/OC ratios that are not specific to Lebanon because of a lack of data could represent a limitation of this methodology. Nevertheless, this comparative analysis suggests that on-road transportation and diesel generators used for electricity production are major sources of atmospheric PM and should be targeted for emission reduction. Finally, cooking activities, which were identified as a significant source of PM with the tracer-based approach, should be studied further.