F. Slemr

Near- and mid-infrared laser-optical sensors for gas analysis

Semiconductor diode lasers were first developed in the mid-1960s and found immediate application as much needed tunable sources for high-resolution laser spectroscopy commonly referred to as tunable diode laser absorption spectroscopy (TDLAS). In this paper, currently available semiconductor lasers for spectroscopy in the near- and mid-infrared spectral region based upon gallium arsenide, indium phosphite, antimonides and lead-salt containing compounds will be reviewed together with the main features of TDLAS. Room-temperature measurements of atmospheric carbon dioxide near 2 μm will be discussed and recent results obtained with a fast chemical sensor for methane flux measurements based on lead-salt diode lasers operating near 7.8 μm will be presented.

Distribution, speciation, and budget of atmospheric mercury

Total gaseous mercury (TGM) concentrations over the Atlantic Ocean and over Central Europe were measured repeatedly in the years 1978–1981. The latitudinal TGM distribution showed a pronounced and reproducible interhemispherical difference with higher TGM concentrations in the Northern Hemisphere. TGM was found to be vertically well mixed within the troposphere. The TGM concentration seems to increase with time at a rate of 10±8%/yr in the Northern and 8±3%/yr in the Southern Hemisphere. Measurements of mercury speciation showed that elemental mercury is the main TGM component contributing more than 92% and 83% of TGM in marine and continental air, respectively. The tropospheric mercury burden was calculated to be 6×109g. The interhemispheric distribution and temporal and spatial variability of TGM imply a tropospheric residence time of TGM of about 1 yr. Sink strengths calculated independently from the measured mercury concentration on particles and in rainwater are consistent with the above figures.

International field intercomparison measurements of atmospheric mercury species at Mace Head, Ireland

Eleven laboratories from North America and Europe met at Mace Head, Ireland for the period 11–15 September 1995 for the first international field intercomparison of measurement techniques for atmospheric mercury species in ambient air and precipitation at a marine background location. Different manual methods for the sampling and analysis of total gaseous mercury (TGM) on gold and silver traps were compared with each other and with new automated analyzers. Additionally, particulate-phase mercury (Hgpart) in ambient air, total mercury, reactive mercury and methylmercury in precipitation were analyzed by some of the participating laboratories. Whereas measured concentrations of TGM and of total mercury in precipitation show good agreement between the participating laboratories, results for airborne particulate-phase mercury show much higher differences. Two laboratories measured inorganic oxidized gaseous mercury species (IOGM), and obtained levels in the low picogram m-3 range.

Distribution of mercury over the Atlantic Ocean in 1996 and 1999–2001

Abstract A series of measurements of total gaseous mercury (TGM) made over the Atlantic Ocean in 1977–1980, 1990, and 1994 has been continued by measurements made on board the research vessel (RV) Polarstern during three cruises: from Bremerhaven to Punta Quilla (October–November 1996), Bremerhaven–Cape Town–Antarctica–Cape Town (December 1999–March 2000), and Antarctica–Punta Arenas (February 2001). The data from these cruises are presented and compared with the data from previous cruises. In both hemispheres the average and median TGM concentrations in 1996 and 2000 were comparable to those measured in 1977–1980 but substantially lower than those observed in 1990. TGM measurements on board ships proved to provide a valuable complementary information to measurements by a ground based monitoring network since they show a large-scale distribution and can provide information about sources of mercury and its long-range transport in areas not covered by the present monitoring network.

Observed decrease in atmospheric mercury explained by global decline in anthropogenic emissions

Significance Anthropogenic mercury poses risks to humans and ecosystems when converted to methylmercury. A longstanding conundrum has been the apparent disconnect between increasing global emissions trends and measured declines in atmospheric mercury in North America and Europe. This work shows that locally deposited mercury close to coal-fired utilities has declined more rapidly than previously anticipated because of shifts in speciation from air pollution control technology targeted at SO2 and NOx. Reduced emissions from utilities over the past two decades and the phase-out of mercury in many commercial products has led to lower global anthropogenic emissions and associated deposition to ecosystems. This implies that prior policy assessments underestimated the regional benefits of declines in mercury emissions from coal-fired utilities. Observations of elemental mercury (Hg0) at sites in North America and Europe show large decreases (∼1–2% y−1) from 1990 to present. Observations in background northern hemisphere air, including Mauna Loa Observatory (Hawaii) and CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) aircraft flights, show weaker decreases (<1% y−1). These decreases are inconsistent with current global emission inventories indicating flat or increasing emissions over that period. However, the inventories have three major flaws: (i) they do not account for the decline in atmospheric release of Hg from commercial products; (ii) they are biased in their estimate of artisanal and small-scale gold mining emissions; and (iii) they do not properly account for the change in Hg0/HgII speciation of emissions from coal-fired utilities after implementation of emission controls targeted at SO2 and NOx. We construct an improved global emission inventory for the period 1990 to 2010 accounting for the above factors and find a 20% decrease in total Hg emissions and a 30% decrease in anthropogenic Hg0 emissions, with much larger decreases in North America and Europe offsetting the effect of increasing emissions in Asia. Implementation of our inventory in a global 3D atmospheric Hg simulation [GEOS-Chem (Goddard Earth Observing System-Chemistry)] coupled to land and ocean reservoirs reproduces the observed large-scale trends in atmospheric Hg0 concentrations and in HgII wet deposition. The large trends observed in North America and Europe reflect the phase-out of Hg from commercial products as well as the cobenefit from SO2 and NOx emission controls on coal-fired utilities.

Distributions of NO, NO x , and NO y in the upper troposphere and lower stratosphere between 28° and 61°N during POLINAT 2

During the Pollution From Aircraft Emissions in the North Atlantic Flight Corridor 2 (POLINAT 2) field campaign the distribution of NO, NOx , and NOy in the upper troposphere and lowermost stratosphere over the eastern North Atlantic was measured using the Deutsches Zentrum fur Luft- und Raumfahrt research aircraft Falcon. Based from Shannon Airport in Ireland, 14 flights were carried out between September 19 and October 25, 1997. The measurements were performed in and out of the North Atlantic flight corridor covering latitudes between 28°N and 61°N. A marked latitudinal gradient in NO, NOx , and NOy , the sum of all reactive nitrogen compounds, was observed. Mean NO volume mixing ratios in the upper troposphere increased from about 50 parts per trillion by volume (pptv) at 28°N to about 180 pptv at 59°N. A similar latitude dependence was also found for NO x and NO y . In the northern part of the POLINAT 2 measuring area, NO and NO x volume mixing ratios increased significantly with increasing altitude withmaximum values around the tropopause, while in the southern part of the measuring area no strong altitude gradient was observed. NO and NOx did not show a substantial gradient across the tropopause. NO/NOy and NOy /O3 ratios showed maximum values of about 0.30 ppbv/ppbv and 0.012 ppbv/ppbv, respectively, around the tropopause. The POLINAT 2 observations suggest that aircraft emissions are an important source of NOx and NOy in the region studied. Also, the present measurements contribute to the data set obtained in the North Atlantic flight corridor during the last few years and help to establish a NOx climatology around the tropopause for this region.

Progress on Understanding Atmospheric Mercury Hampered by Uncertain Measurements

by Uncertain Measurements Daniel A. Jaffe,*,†,‡ Seth Lyman, Helen M. Amos, Mae S. Gustin, Jiaoyan Huang, Noelle E. Selin, Leonard Levin, Arnout ter Schure, Robert P. Mason, Robert Talbot, Andrew Rutter, Brandon Finley,† Lyatt Jaegle,‡ Viral Shah,‡ Crystal McClure,‡ Jesse Ambrose,† Lynne Gratz,† Steven Lindberg, Peter Weiss-Penzias, Guey-Rong Sheu, Dara Feddersen, Milena Horvat, Ashu Dastoor, Anthony J. Hynes, Huiting Mao, Jeroen E. Sonke, Franz Slemr, Jenny A. Fisher, Ralf Ebinghaus, Yanxu Zhang, and Grant Edwards⪫

Hydrogen Peroxide, Organic Peroxides and Higher Carbonyl Compounds Determined during the BERLIOZ Campaign

Gas-phase H2O2, organic peroxides and carbonyl compounds were determined at various sites from Mid-July to early August 1998 during the BERLIOZ campaign in Germany. The sites were located northwest of Berlin and were chosen to determine pollutants downwind of the city emissions during a summer smog episode. Hydrogen peroxide (H2O2), methyl hydroperoxide (MHP, CH3OOH) and occasionally hydroxy methyl hydroperoxide (HMHP, HOCH2OOH) were quantified in air samples by commercial fluorimetric methods and classical HPLC with post-column derivati-sation by horseradish peroxidase/p-hydroxyphenyl acetic acid and fluorimetric detection. Carbonyl compounds were determined in ambient air by a novel method based on O-pentafluorobenzyl hy-droxylamine as derivatisation agent. Mixing ratio profiles of the hydroperoxides and the carbonyl compounds are reported for the intensive phase of the campaign, 20–21 July, 1998. Peroxides showed pronounced diurnal variations with peak mixing ratios in the early afternoon. At times, a second maximum was observed in the late afternoon. The major part of the H2O2 was formed through recombination reactions of HO2 radicals, but there is some evidence that H2O2 is also formed from ozonolysis of anthropogenic and/or biogenic alkenes. Diurnal variations of mixing ratios of various carbonyl compounds are reported: alkanals (C2 to C10, isobutanal), unsaturated carbonyl compounds (methacrolein, methylvinylketone, acrolein), hydroxycarbonyl (glycolaldehyde, hydroxyacetone) and dicarbonyl compounds (glyoxal, methylglyoxal, biacetyl), aromatic compounds (benzaldehyde, o- and m-tolylaldehyde) and pinonaldehyde.

Regional nitric oxide enhancements in the North Atlantic flight corridor observed and modeled during POLINAT 2-A case study

In situ measurements of nitrogen oxides and other trace chemicals were performed aboard the DLR Falcon in September and October 1997 during POLINAT 2 over the eastern North Atlantic in areas with predicted high impact of aircraft emissions to search for flight corridor effects. During survey flights in the upper troposphere from the centre of the flight corridor to regions south of or below the major transatlantic aircraft routes, large-scale enhancements in mixing ratios of NO of about 50 to 150 pptv were observed in corridor areas compared to the NO abundance measured outside the corridor. Using simultaneous tracer measurements, back trajectory analyses for the air masses sampled, the actual distribution of the North Atlantic air traffic, and comparisons of observed and predicted NO distributions from a regional model of simulations including or excluding aircraft emissions, these enhancements were attributed mainly to aircraft NOx.

In-flight measurement of aircraft non-methane hydrocarbon emission indices

Concentrations of non-methane hydrocarbons (NMHC) and CO were measured in exhaust plumes of the DLR experimental aircraft ATTAS equipped with Rolls Royce M 45H Mk501 engines. The emission indices (EI) of individual light NMHC were determined from ratios of NMHC and CO concentration enhancements measured in grab samples and the concurrent in-flight measurements of EI of CO by FTIR emission spectroscopy. Alkenes and alkynes generated by cracking of larger NMHC molecules and aromatic compounds originating from unburnt fuel constituted a larger and a smaller fraction of the NMHC emissions, respectively.