J. Mellqvist | Chalmers University of Technology (original) (raw)

Papers by J. Mellqvist

Proceedings of the …, 2002

A coordinated action involving eleven stations of the ground-based Network for Detection of Strat... more A coordinated action involving eleven stations of the ground-based Network for Detection of Stratospheric Change (NDSC) equipped with Fourier transform infrared (FTIR) instruments was conducted to contribute to the validation of the three atmospheric ...

Atmospheric Chemistry and Physics, 2011

Satellite and aircraft observations made during the 2006 Texas Air Quality Study (TexAQS) detecte... more Satellite and aircraft observations made during the 2006 Texas Air Quality Study (TexAQS) detected strong urban, industrial and power plant plumes in Texas. We simulated these plumes using the Weather Research and Forecasting-Chemistry (WRF-Chem) model with input from the US EPA's 2005 National Emission Inventory (NEI-2005), in order to evaluate emissions of nitrogen oxides (NO x = NO + NO 2) and volatile organic compounds (VOCs) in the cities of Houston and Dallas-Fort Worth. We compared the model results with satellite retrievals of tropospheric nitrogen dioxide (NO 2) columns and airborne in-situ observations of several trace gases including NO x and a number of VOCs. The model and satellite NO 2 columns agree well for regions with large power plants and for urban areas that are dominated by mobile sources, such as Dallas.

While chemical ozone depletion in the Antarctic spring-time stratosphere is now an annually occur... more While chemical ozone depletion in the Antarctic spring-time stratosphere is now an annually occurring and well-understood phenomenon, dynamical variability in the Arctic stratosphere means ozone depletion in the northern polar vortex is both less predictable and more susceptible to changes resulting from climate change than in the southern vortex. In order to examine ozone-depleting processes and quantify chemical changes occurring

Journal of Geophysical Research, 2002

Journal of Geophysical Research, 1997

Hydrogen fluoride (HF) is often used as a simple reference for other column observations of chemi... more Hydrogen fluoride (HF) is often used as a simple reference for other column observations of chemically active stratospheric species. However, seasonal and shorter timescale variations in column HF make its use as a reference more complicated. In this paper we characterize the expected magnitude of these variations in HF, and variations of ratio quantities involving HF, using a twodimensional (2-D) photochemical model and two versions of a three-dimensional (3-D) transport model. The 2-D model predicts that the column ratios HNO3/HF and HC1/HF increase from midlatitudes to the tropics, although this is very sensitive to HC1 and HNO3 abundances in the tropical upper troposphere. Seasonal variations in vertical motion modifys the predicted ratios; for example, wintertime descent at high latitudes decreases HC1/HF. The ratio HNO3/HF at high latitudes is strongly modified by seasonal variations in the chemical partitioning of the odd nitrogen (NOy) species. We compare these model predictions with ground-based Fourier transform infrared spectroscopy (FTIR) observations of HF along with HC1, C1ONO2 and HNO3 obtained at eight northern hemisphere sites between October 1994 and July 1995. We investigate quantitatively how HF can be used as a tracer to follow the evolution of observations at a single station and to intercompare results from different stations or with photochemical models. The magnitude of the 3-D model HF column agrees well with the observations, except on some occasions at high latitudes, giving indirect support for the important role of COF2 in the stratospheric inorganic fluorine budget. The observed day-today variability in the column ratios HC1/HF and HNO3/HF is much larger at high latitudes. This variability is reproduced in the 3-D models and is due to horizontal motion. Short timescale vertical displacement of the species profiles is estimated to have a small effect on the column ratios. In particular, we analyze the usefulness of the observed column ratio (C1ONO2 + HC1)/HF as an indicator for chlorine activation. Current measurement uncertainties limit the degree of activation which can be unambiguously detected using this observed quantity, but we can determine that chlorine-activated air was observed above Aberdeen (58øN) on 6 days in late

Atmospheric Chemistry and Physics, 2006

Photochemical pollution control strategies require an understanding of photochemical oxidation pr... more Photochemical pollution control strategies require an understanding of photochemical oxidation precursors, making it important to distinguish between primary and secondary sources of HCHO. Estimates for the relative strengths of primary and secondary sources of formaldehyde (HCHO) were obtained using a statistical regression analysis with time series data of carbon monoxide (CO) and glyoxal (CHOCHO) measured in the Mexico City Metropolitan Area (MCMA) during the spring of 2003. Differences between Easter week and more typical weeks are evaluated. The use of CO-CHOCHO as HCHO tracers is more suitable for differentiating primary and secondary sources than COO 3. The application of the COO 3 tracer pair to mobile laboratory data suggests a potential in-city source of background HCHO. A significant amount of HCHO observed in the MCMA is associated with primary emissions.

Atmospheric Chemistry and Physics, 2008

Atmospheric Chemistry and Physics, 2007

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Atmospheric Chemistry and Physics, 2009

Increased Northern Hemispheric carbon monoxide burden in the troposphere in 2002 and 2003 detecte... more Increased Northern Hemispheric carbon monoxide burden in the troposphere in 2002 and 2003 detected from the ground and from space

Introduction Conclusions References

The Solar Occultation Flux (SOF) method and mobile DOAS technique were used to measure industrial... more The Solar Occultation Flux (SOF) method and mobile DOAS technique were used to measure industrial emissions of volatile organic compounds, formaldehyde, NO2 and SO2 in the Houston area during the time period April 15 to June 11, 2009. The measurements were conducted as part of the campaign FLAIR (Formaldehyde and alkenes from Large Industrial Releases) with the aim to better understand the role of formaldehyde for the photochemical production of ozone. The SOF technique is an optical method utilizing the absorption of direct solar infrared radiation in the 1.8-14 µm range for the retrieval of total columns of various species such as ethylene, propylene, ammonia and alkanes. Mobile DOAS utilizes scattered light in the ultraviolet spectral region for measurements of HCHO, SO2 and NO2. A crude chemical model has been applied to interprete whether the measured formaldehyde in the industrial emission plumes is primary emitted or secondary produced from oxidation of alkenes. The measured emissions of alkenes in the Houston Ship channel area were a factor of 10 higher than reported in the emission inventories and corresponded to about 600 kg/h for both ethene and propene. Several individual industrial sources of formaldehyde were identified in the Houston area. The emissions from these sources were relativaly small and ranged from a few kg/h up to over 40 kg/h. In most cases it was interpreted with the model that these corresponded to primary emissions of formaldehyde. However, a few large scale measurements further downwind the Houston ship channel showed formaldehyde fluxes (over 1000 kg/h) that could not be explained by the sum of the individual sources measured. These numbers are consistent with secondary production of formaldehyde from the alkene sources. Our conclusion is hence that the dominant part of the formaldehyde around the the Houston ship channel is being secondary produced from alkenes rather than coming from direct emissions.

Atmospheric Chemistry and Physics Discussions, 2007

This paper describes the statistical analysis of annual trends in long term datasets of greenhous... more This paper describes the statistical analysis of annual trends in long term datasets of greenhouse gas measurements taken over ten or more years. The analysis technique employs a bootstrap resampling method to determine both the long-term and intra-annual variability of the datasets, together with the uncertainties on the trend values. The method has been applied to data from a European

Instrument Development for Atmospheric Research and Monitoring, 1997

The work accomplished during the period 1990 to 1995 by the three Belgian groups participating in... more The work accomplished during the period 1990 to 1995 by the three Belgian groups participating in the EUROTRAC-TOPAS project is described. It involved the construction and permanent improvement of two DOAS (Differential Optical Absorption Spectroscopy) spectrometers. One of these is a Fourier transform instrument which was applied to atmospheric measurements in the Visible-UV region for the first time. Long path absorption set-ups were constructed. Software was developped to operate and automate the instruments and specific algorithms were written for the retrieval of concentrations from the atmospheric spectra. Both instruments were validated by participating in two EUROTRAC-TOPAS intercomparison campaigns which gathered instruments from six european countries. Finaly, high resolution absorption cross sections of several atmospherically relevant species were measured in the laboratory.

Journal of Geophysical Research: Atmospheres, 2014

A sensitive Mobile differential optical absorption spectroscopy (DOAS) system with real-time eval... more A sensitive Mobile differential optical absorption spectroscopy (DOAS) system with real-time evaluation capability and HCHO detection limit of 3 ppb over 100 m has been developed. The system was operated together with a Solar Occultation Flux system for large-scale vertical flux measurements of HCHO, NO 2 , SO 2 , and VOCs in the Houston-Galveston-Brazoria area during two studies, in 2009 (Study of Houston Atmospheric Radical Precursors campaign) and in 2011 (Air Quality Research Program study). Both in 2009 and 2011, HCHO plumes from five separate local sources in Texas City, Mont Belvieu, and Houston Ship Channel (HSC) were repeatedly detected using Mobile DOAS with emissions varying between 6 and 40 kg/h. In many cases significant alkene emissions were detected simultaneously with the HCHO plumes. Furthermore, in 2011 two additional sources were observed in Texas City and in HSC, with 10 kg/h and 31 kg/h HCHO, respectively. A plume chemistry model was applied to 13 cases to investigate whether the detected HCHO was emitted directly from the industries or was produced by photochemical degradation of VOCs. The model results showed that on average 90% of the detected HCHO was of primary origin and the photochemical production contributed more than 10% in only three cases. Based on the repeatability, it is likely that the most significant HCHO sources in the area are included in this study with an overall emission of 120 kg/h. On a regional scale, this emission is small compared to the secondary HCHO formed from oxidation of reactive VOCs emitted from the same industries, estimated to be an order of magnitude higher. Two large measurement campaigns undertaken in the HGB area, TexAQS (Texas Air Quality Study) in 2000 and TexAQS II in 2006, aimed to quantify emissions and to explain the causes of ozone exceedance events. Several studies based on measurements from these campaigns showed that existing emission inventories severely underestimated VOC emissions in the area, often by up to an order of magnitude [

Semiconductor Science and Technology, 1999

We present absorption spectra as a function of temperature for CdTe quantum dots in doped glasses... more We present absorption spectra as a function of temperature for CdTe quantum dots in doped glasses. We calculate the absorption spectra considering the transition energies from a spherical 0268-1242/14/1/007/img9 model. We consider also the inhomogeneous broadening due to the quantum-dot size distribution and the homogeneous broadening, due mainly to electron-phonon interactions. The samples grown with a two-step heat treatment present very thin size distributions, with a standard deviation of 5.8%, which is comparable to the best CdSe samples in the literature. Also, the results show that the homogeneous width increases as the quantum-dot size decreases, indicating an enhancement of the electron-phonon interaction for small dots.