Chemical characterization of diesel and hydrotreated vegetable oil (HVO) soot after reactive gas probing using diffuse reflectance FTIR spectroscopy (DRIFTS).

A chemical characterization of diesel and hydrotreated vegetable oil (HVO) soot has been developed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) before and after the reaction with different probe gases. Samples were generated under combustion conditions corresponding to an urban operation mode of a diesel engine and were reacted with probe gas-phase molecules in a Knudsen flow reactor. Specifically, NH2OH, O3 and NO2 were used as reactants (probes) and selected according to their reactivities towards specific functional groups on the sample surface. Samples of previously ground soot were diluted with KBr and were introduced in a DRIFTS accessory. A comparison between unreacted and reacted soot samples was made in order to establish chemical changes on the soot surface upon reaction. It was concluded that the interface of diesel and HVO soot before reaction mainly consists polycyclic aromatic hydrocarbons, nitro and carbonyl compounds, as well as ether functionalities. The main difference between both soot samples was observed in the band of the C=O groups that in diesel soot was observed at 1719 cm-1 but not in HVO soot. After reaction with probe gases, it was found that nitro compounds remain on the soot surface, that the degree of unsaturation decreases for reacted samples, and that new spectral bands such as hydroxyl groups are observed.

Molecular Characterization of the Gas-Particle Interface of Soot Sampled from a Diesel Engine Using a Titration Method.

Surface functional groups of two different types of combustion aerosols, a conventional diesel (EN 590) and a hydrotreated vegetable oil (HVO) soot, have been investigated using heterogeneous chemistry (i.e., gas-particle surface reactions). A commercial sample of amorphous carbon (Printex XE2-B) was analyzed as a reference substrate. A Knudsen flow reactor was used to carry out the experiments under molecular flow conditions. The selected gases for the titration experiments were: N(CH3)3 for the identification of acidic sites, NH2OH for the presence of carbonyl groups, CF3COOH and HCl for basic sites of different strength, and O3 and NO2 for reducing groups. Reactivity with N(CH3)3 indicates a lower density of acidic functionalities for Printex XE2-B in relation to diesel and HVO soot. Results for NH2OH experiments indicates that commercial amorphous carbon exhibits a lower abundance of available carbonyl groups at the interface compared to the results from diesel and HVO soot, the latter being the one with the largest abundance of carbonyl functions. Reactions with acids indicate the presence of weak basic oxides on the particle surface that preferentially interact with the strong acid CF3COOH. Finally, reactions with O3 and NO2 reveal that diesel and especially HVO have a significantly higher reactivity with both oxidizers compared to that of Printex XE2-B because they have more reducing sites by roughly a factor of 10 and 30, respectively. The kinetics of titration reactions have also been investigated.

The use of heterogeneous chemistry for the characterization of functional groups at the gas/particle interface of soot from a diesel engine at a particular running condition.

Two gases, O3 and NO2, were selected to probe the surface of a diesel fuel combustion aerosol sample, diesel soot, and amorphous carbon nanoparticles (PRINTEX XE2-B) using heterogeneous (i.e., gas-surface reactions). The gas uptake to saturation of the probes was measured under molecular flow conditions using a Knudsen flow reactor in order to quantify and characterize surface functional groups. Specifically, O3 and NO2 are used for the titration of oxidizable groups. Diesel soot samples interacted with the probe gases to various extents which points to the coexistence of different functional groups on the same aerosol surface such as reduced groups. The carbonaceous particles displayed significant differences: PRINTEX XE2-B amorphous carbon had a significantly lower surface functional group density of both total and strongly reducing groups despite its significantly larger internal surface area, compared to diesel soot. The uptake kinetics of the gas-phase probe molecules (uptake probabilities) were also measured in order to obtain further information on the reactivity of emitted soot aerosols in order to enable the potential prediction of health effects.

FTIR gas-phase kinetic study on the reactions of some acrylate esters with OH radicals and Cl atoms.

Acrylate esters are α,ß-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298 ± 2 K) and atmospheric pressure (708 ± 8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm(3) molecule(-1) s(-1)): (3.27 ± 0.33) × 10(-11) and (4.43 ± 0.42) × 10(-11), for CH3CH═CHC(O)OCH3 and (CH3)2CH═CHC(O)OCH3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N2 and air were used as the bath gases. The following rate coefficients were obtained (in cm(3) molecule(-1) s(-1)): k3 (CH2═CHC(O)O(CH2)5CH3 + Cl) = (3.31 ± 0.31) × 10(-10), k4(CH2═CHC(O)OCH2CH(CH2CH3)(CH2)3CH3 + Cl) = (3.46 ± 0.31) × 10(-10), k5(CH2═CHC(O)O(CH2)5CH3 + OH) = (2.28 ± 0.23) × 10(-11), and k6(CH2═CHC(O)OCH2CH(CH2CH3)(CH2)3CH3 + OH) = (2.74 ± 0.26) × 10(-11). The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in -C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do not influence global warming.

Night-time atmospheric fate of acrolein and crotonaldehyde.

The absolute rate coefficients for the gas-phase reaction of the NO3 radical with acrolein and crotonaldehyde have been measured overthe temperature range 249-330 K, using a discharge flow system and monitoring the NO3 radical by laser induced fluorescence (LIF). The obtained rate coefficients at 298 K for NO3 reactions with acrolein and crotonaldehyde were (3.30 +/- 0.39) x 10(-15) cm3 molecule(-1) s(-1) for acrolein and (1.35 +/- 0.04) x 10(-14) cm3 molecule(-1) s(-1) for crotonaldehyde, and the proposed Arrhenius expressions are k(T) = (1.72 +/- 0.5) x 10(-13) exp[(-1190 +/- 43)/T] and k(T) = (5.02 +/- 0.7) x 10(-13) exp[(-1076 +/- 47)/T], respectively, in units of cm3 molecule(-1) s(-1). In addition, the products and mechanisms were investigated using an environmental chamber/FTIR absorption system. Formaldehyde, CO, and acryloylperoxy nitrate were identified as the main products for the acrolein reaction with molar yields of 31.6 +/- 2.0, 20.9 +/- 1.9, and 47 +/- 3, respectively. In the crotonaldehyde reaction the main products detected were crotonylperoxy nitrate and CO with yields of 93.6 +/- 4.3 and 8.3 +/- 1.1, respectively. On the basis of the rate constant measured, the activation energy calculated, and the identified products, abstraction of the aldehydic H seems to be the main degradation pathway at room temperature for the reaction of acrolein with NO3. For crotonaldehyde, the mechanism is unclear on the basis of the experimental results. The atmospheric implications of the reactions in question are also discussed.

Forensic medicine in the Indo-Pacific region: history and current practice of forensic medicine.

A brief history of forensic medicine in the Indo-Pacific region followed by the extent of medical education imparted to undergraduates and current practice in various countries of the region are examined.

Identification from skeletal remains.

The remains of a suspected case of homicide, found to be almost totally skeletal on exhumation, was dug out from a pit in a tract of marshy land in the deep south or Sri Lanka. No clothing or other identifying articles were found with the remains. During exhumation a distinct odour of kerosene oil was observed. Examination revealed that the major part of the skeleton was present, including the skull and lower jaw. Examination of these enabled an opinion to be given on the stature, sex and age of the deceased. The head hair found at exhumation showed evidence of burning. Two groups of injuries were found in the bones. One group was consistent with injuries caused during life and showing the characters of healing and moulding. Although medical records were not available, it was possible to obtain a description of the injuries from the court records as a doctor had given evidence on injuries sustained by the deceased years previously. The other group comprised of injuries that would have caused or contributed to death, or were post-mortem injuries inflicted for purposes of disposal. This case illustrates that personal identification may be established from old healed skeletal injuries.

Agrochemical poisoning in Sri Lanka.

Mortality resulting from agrochemicals met within the Office of the Judicial Medical Officer, Colombo, which is the premier Medico-legal Institute in Sri Lanka, are analysed over a 3-year period and the morbidity and mortality rates of the entire country are examined over a 10-year period. The number of patients admitted to hospitals in Sri Lanka during the period 1975-1983, stood at around 11,000-15,000 each year, with the year 1983 recording 16,649 admissions. The number of deaths during the same period varied from 900 to 1500 each year, while the year 1983 recording 1521 deaths. About 75% of such cases of poisoning were due to self ingestion while accidental and occupational poisoning formed the balance. Principal agricultural districts like Kurunegala, Jaffna, Vavuniya, Nuwara-Eliya and Badulla recorded the highest incidence of poisoning. The mortality figures of the Office of the J.M.O., Colombo, indicated that 4% of all bodies subjected to autopsy were those of agrochemical poisoning. The male/female ratio was 2:1. Seventy-five percent of deaths from agrochemical poisoning were recorded in the 15-39 year age group, while 33% of deaths belonged to the 20-24 age group. One third of cases of agrochemical poisoning were dead on being brought to hospital, while 50% were dead within 2 h and 60% dead within 24 h. Organophosphates accounted for 57.6% of all cases of agrochemical poisoning, while paraquat accounted for 21.2% of cases. Deaths were also reported from what are called safe chemicals like Carbamates and Pyrethrums due to their lethal additives.

Analysis of fatalities in road accidents.

This paper is based on the analysis of 524 autopsies carried out on the victims of road accidents at the Office of the Judicial Medical Officer, Colombo for a 2-year period ending December 1985. 51.4% of the fatalities were among pedestrians. The highest number of fatalities were in the age group 20-29 years. Cranio-cerebral injury was the commonest cause of death in all groups of victims.

Forensic medicine and medicolegal investigation in Sri Lanka.

In a small country such as Sri Lanka, very interesting applications of forensic medicine and medicolegal investigation exist. We present information that provides an important addition to the knowledge of medicolegal investigators all over the world.