Haider Khwaja - Academia.edu (original) (raw)

Papers by Haider Khwaja

IBRAS, 2021

Karachi, Pakistan is one of the largest and most polluted metropolitan cities in south Asia. Air ... more Karachi, Pakistan is one of the largest and most polluted metropolitan cities in south Asia. Air quality was assessed using 24-hour fine particulate matter (PM2.5) samples collected from two sites, Korangi and Tibet Center. Daily emergency room (ER) visits and hospital admissions for cardiovascular diseases were obtained at three major tertiary hospitals. Particulate levels were extraordinarily high. Mean PM2.5 levels in Karachi exceeded the WHO's 24 h air quality guidelines by a factor of greater than 5-fold. Results show that the extremely elevated concentrations of PM2.5 are associated with significantly elevated rates of hospital admissions and ER visits for cardiovascular diseases.

Environmental Monitoring and Assessment, Nov 14, 2022

Aerosol and Air Quality Research, 2016

The present study describes the measurement, chemical characterization and delineation of sources... more The present study describes the measurement, chemical characterization and delineation of sources of fine particulate matter (PM 2.5) in Rabigh, Saudi Arabia. The 24-h PM 2.5 was collected from May 6 th-June 17 th , 2013. The sources of various air pollutants and their characterization was carried by computations of Enrichment Factor (EF), Positive Matrix Factorization (PMF) and Backward-in-time Trajectories. The 24-h PM 2.5 showed significant temporal variability with average (37 ± 16.2 µg m-3) exceeding the WHO guideline (20 µg m-3) by 2 fold. SO 4 2-, NO 3-, NH 4 + and Clions dominated the ionic components. Two broad categories of aerosol Trace Elements (TEs) sources were defined as anthropogenic (Ni, V, Zn, Pb, S, Lu and Br) and soil/crustal derived (Si, Rb, Ti, Fe, Mn, Mg, K, Sr, Cr, Ca, Cu, Na and Al) elements from computations of EF. Anthropogenic elements originated primarily from fossil-fuel combustion, automobile and industrial emissions. A factor analysis model (PMF) indicated the major sources of PM 2.5 as Soil (Si, Al, Ti, Fe, Mg, K and Ca); Industrial Dust (Ca, Fe, Al, and Si); Fossil-Fuel combustion (V, Ni, Pb, Lu, Cu, Zn, NH 4 + , SO 4 2and BC); Vehicular Emissions (NO 3-, C 2 O 4 2-, V and BC) and Sea Sprays (Cland Na). Backward-in-time trajectories showed a significant contribution by long distance transport of fine aerosols to the overall daily PM 2.5 levels. Results are consistent with previous studies and highlight the need for more comprehensive research into particulate air pollution in Rabigh and the neighboring areas. This is essential for the formulation of sustainable guidelines on air pollutant emissions in Saudi Arabia and the whole Middle East.

Science of The Total Environment, Apr 1, 2023

Environmental health perspectives, Oct 26, 2020

Chemischer Informationsdienst, Oct 26, 1982

Environmental health perspectives, Sep 24, 2018

Environmental epidemiology, Oct 1, 2019

Atmosphere, Apr 29, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Journal of Water Resource and Protection, 2019

Inserting Groundwater quality variability and sources potentially contributing to aquifer recharg... more Inserting Groundwater quality variability and sources potentially contributing to aquifer recharge was evaluated in metropolitan Karachi. Selected sampling sites were characterized by large waste dumping sites, industrial zones, and the presence of open streams receiving heavy loads of industrial and domestic wastes. Levels of pH, electrical conductivity (EC), fluoride (F −), chloride (Cl −), bromide (Br −), nitrate-N (3 NO-N −), sulfate (2 4 SO −), sodium (Na +), potassium (K +), calcium (Ca 2+), magnesium (Mg 2+), and ammonium (4 NH +) were determined and compared with the WHO permissible limits. Concentrations of the measured ions were in the order of Cl − > Na + > 2 4 SO − > Mg 2+ > Ca 2+ > 3 NO-N − > K + > F − > Br −. EC values were above the WHO guidelines, representing the presence of high ionic concentration in the groundwater. The health risk index (HRI) for 3 NO-N − indicated that inhabitants of Karachi are at risk of high 3 NO-N − exposure. Ingestion of high concentrations of NO 3 −-N in water can cause methemoglobinemia and birth defects. Results of multivariate statistical analysis, principal component analysis (PCA), cluster analysis (CA), and geographic information system (GIS) map analysis revealed that human activities are leading to adverse effects on the existing groundwater quality in Karachi.

Zeitschrift für Physikalische Chemie, Feb 1, 1981

Energy barrier / Group relaxation / Dielectric absorption / Heterocyclic aldehydes and ketones / ... more Energy barrier / Group relaxation / Dielectric absorption / Heterocyclic aldehydes and ketones / Polystyrene matrix The dielectric absorption of a number of heterocyclic aldehydes and ketones has been studied in a polystyrene matrix over a wide temperature range. In four cases the group relaxation process has been completely separated from the molecular relaxation one. For these four cases the energy barrier to group rotation has been determined and found to be appreciably higher than those where the aldehyde or keto group is attached to a phenyl, biphenyl, or fluorenyl conjugated system. The increased barrier is attributed to enhanced conjugation between the hetero-atom and the aldehyde or keto group. In addition, the results for five rigid molecules of suitable size and shape are given, as these form the basis for identification of the molecular process in the flexible molecules. Für eine Reihe von heterozyklischen Aldehyden und Ketonen in einer Polystyrolmatrix wurde die dielektrische Absorption über einen weiten Temperaturbereich gemessen. In vier Fällen konnte die (Rotations-)Relaxation der CO-haltigen Gruppen von der des Moleküls als Ganzem vollständig separiert werden. In diesen vier Fällen wurde die Energieschwelle der Gruppenrotation bestimmt und erheblich höher gefunden als bei Bindung der Aldehyd-oder Ketogruppe an ein konjugiertes Phenyl-, Biphenyl-oder Fluorenylsystem. Die höhere Energieschwelle wird der verstärkten Konjugation zwischen dem Heteroatom und der Aldehyd-oder Ketogruppe zugeschrieben. Außerdem werden die Meßergebnisse für fünf starre Moleküle vergleichbarer Größe und Form mitgeteilt, mit deren Hilfe auch bei den flexiblen Molekülen der molekulare Relaxationsprozeß identifiziert werden konnte.

Canadian Journal of Chemistry, Aug 1, 1984

Quenching of the fluorescence of benzene by halocarbons in methanol, ethanol, acetonitrile, and c... more Quenching of the fluorescence of benzene by halocarbons in methanol, ethanol, acetonitrile, and cyclohexane has been investigated. It proceeds via a reversible exciplex intermediate formed between excited singlet benzene and ground state halocarbon. Quenching is controlled by the polarity of the medium. Excited singlet benzene interacts with acetonitrile solvent and a longer wavelength emission due to this complex is observed. The effect of CCI,, CH,CN, CHCI,, and CH,CC13 on the triplet and singlet excited states of benzene in a methylcyclohexane-isopentane mixture at 77 K has been examined. Carbon tetrachloride and acetonitrile are far more effective quenchers than either CHC13 or CH,CCl,. In the case of the latter pair enhanced intersystem crossover competes with complex formation.

Chemosphere, Feb 1, 2022

Per- and polyfluoroalkyl substances (PFAS) have received continuous attention; however, there is ... more Per- and polyfluoroalkyl substances (PFAS) have received continuous attention; however, there is limited understanding of their sources in the atmosphere and related human exposure risks. This study measured PFAS in the atmospheric collected from Karachi, Pakistan, during the winter. Among the quantified PFAS, perfluorobutanoic acid (PFBA) showed the highest average concentration (3.11 ± 2.64 pg/m3), accounting for 32% of the total PFAS. Wind speed was positively correlated with perfluorohexanoic acid (PFHxA) and N-ethyl perfluorooctanesulfonamide (N-EtFOSA), while relative humidity was negatively correlated with perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). Weighted potential source contribution function (WPSCF) and concentration weighted trajectory (WCWT) analyses suggested that northwestern Pakistan and western Afghanistan areas were highly associated with the long-range atmospheric transport of PFAS. We also calculated the estimated daily intake of PFAS, which were in the range of 0.072-3.98 and 0.006-0.325 pg/kg bw/d for children and adults, respectively. The calculated hazard quotient (HQ) of PFOS and PFOA was significantly lower than 1, indicating less or unlikely to cause non-carcinogenic effect via inhalation exposure. Overall, this study contributes to the understanding of geographic origins and human inhalation risks of airborne PFAS on a regional scale.

Atmosphere, Dec 28, 2022

Science of The Total Environment, Apr 1, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Environmental health perspectives, Aug 23, 2021

DOAJ (DOAJ: Directory of Open Access Journals), Dec 1, 2017

This study is illuminating the distinctiveness of Particulate matter having 2.5µm size (PM 2.5) w... more This study is illuminating the distinctiveness of Particulate matter having 2.5µm size (PM 2.5) with water soluble ions like SO 4-2 , NO 3 and Clalong with carbonaceous aerosols (i.e. BC IR and BC UV) as well as elemental profile for the period December 2012 to January 2013 at residential cum industrial site to investigate the quality of air of the mega city Karachi. Twenty-six samples have been collected for 24-hours during the study period on PTFE samples. Mean concentration of PM 2.5 is found to be 112µg/m 3 which is much higher than the WHO guideline (i.e.25 µg/m 3). Both, BC UV and BC IR , have high contents during the study period i.e. 3.85µg/m 3 and 5.09µg/m 3 mean values respectively.

2014 AGU Fall Meeting, Dec 15, 2014

First measurements of NMHCs in Ningbo, an industrialized coastal city in the YRD, China, are repo... more First measurements of NMHCs in Ningbo, an industrialized coastal city in the YRD, China, are reported. • Diagnostic ratios were used to analyze the chemical evolution of NMHCs. • Conditional probability function (CPF) was used to facilitate the determination of PMF-resolved factors. • Seasonal variations of source contributions should be considered when formulating the NMHC abatement strategy.