Decay of the Northern Hemisphere stratospheric polar vortex and the occurrence of cut-off low systems: An exploratory study

Summary The authors perform an exploratory analysis on the effect of the timing of the stratospheric vortex breakup in the occurrence of cut-off low systems (COLs) in the Northern Hemisphere. The first multidecadal Northern Hemisphere COLs database (Nieto et al, 2005) covering a 41 year-long period (1958–1998) was used in the analysis. The dates of stratospheric vortex breakup were obtained using two different approaches recently purposed in literature based in potential vorticity and zonal winds. An analysis of differences of COLs occurrences for the five earlier (later) breakup years showed that, at latitudes lower than 45° N, COLs are more frequent for earlier vortex years during the following spring and summer. The monthly analysis showed that, in general, the significant differences start in May lasting until September, being especially relevant for the European sector, the area with the highest rates of COLs occurrence in the Northern Hemisphere.     

Changes in ice-season characteristics of a European Arctic lake from 1964 to 2008

The long-term ice record (from 1964 to 2008) of an Arctic lake in northern Europe (Lake Kilpisj?rvi) reveals the response of lake ice to climate change at local and regional scales. Average freeze-up and ice breakup occurred on 9 November and 19 June, respectively. The freeze-up has been significantly delayed at a rate of 2.3 d per decade from 1964 onward (P?<?0.05). No significant change has taken place in ice breakup. Annual average ice thickness has become smaller since the mid-1980s (P?<?0.05). Air temperature during the early ice season significantly affected the ice thickness. The freeze-up date exhibits the highest correlation with the 2-month average daily minimum air temperature centered at the end of October, while the ice breakup date exhibits the highest correlation with the 2-month average daily maximal air temperature centered in mid May. A 1°C increase in the surface air temperature corresponds to a freeze-up later by 3.4?days and an ice breakup earlier by 3.6?days. Snow cover is a critical factor in lake-ice climatology. For cumulative November to March precipitation of less than 0.13?m, the insulating effect of the snow dominated, while higher rates of precipitation favored thicker ice due to the formation of snow ice. Variations in ice records of Lake Kilpisj?rvi can serve as an indicator of climate variations across the northern Europe. The North Atlantic Oscillation (NAO) does not significantly affect the ice season there, although both the local air temperatures and winter precipitation contain a strong NAO signal.     

Ice-sheet growth and high-latitudes sea-surface temperature

The response of the LLN 2-D climate model to the insolation and CO₂ forcings during the Eemian interglacial is compared to reconstructions obtained from deep-sea cores drilled in the Norwegian Sea and in the North Atlantic. Both reconstructions and modeling results show a decrease of sea-surface temperature (SST) in the higher latitudes (70–75 °N zonal belt for the model and the Norwegian Sea for the proxy records), associated with a more moderate cooling at lower latitudes (50–55 °N and North Atlantic), at the middle of isotopic substage 5e, several millenia before the beginning of continental ice-sheet growth. Such a comparison between the simulated SST and ice volume of the Northern Hemisphere has been extended to the whole last glacial-interglacial cycle. The influence of the insolation forcing on SST and the shortcomings of the model due to its zonal character are discussed. Received: 6 July 1995/Accepted: 19 December 1995     

An assessment of the potential impact of a downward shift of tropospheric water vapor on climate sensitivity

This work uses an energy balance climate model (EBCM) with explicit infrared radiative transfer, parametrized tropospheric temperature and humidity profiles, and separate stratosphere, troposphere, and surface energy balances, to investigate claims that a downward redistribution of tropospheric water vapor in response to surface warming could serve as a strong negative feedback on climatic change. A series of sensitivity tests is carried out using: (1) a variety of relationships between total precipitable water in the troposphere and temperature; (2) feedbacks between surface temperature and the vertical distribution of tropospheric water vapor at low latitudes; and (3) feedback between surface temperature or meridional temperature gradient and lapse rate. Fixed relative humidity (RH) enhances the global mean surface temperature response to a CO₂ doubling by only 50% compared to fixed absolute humidity, giving a response of 1.8 K. When water vapor is assumed to be redistributed downward between 30°S–30°N such that a 1 K surface warming reduces total precipitable water above 600 hPa by 10%, the global mean surface air temperature response is reduced to 1.2 K. Assuming a stronger downward redistribution in relation to surface temperature change has a rapidly diminishing marginal effect on global mean and tropical surface temperature response, while slightly increasing the warming at high latitudes due to the parametrized dependence of middle-to-high latitude lapse rate on the meridional temperature gradient. A modest downward water vapor redistribution, such that absolute humidity in the upper troposphere at subtropical latitudes is constant as total precipitable water increases, can reduce the tropical temperature sensitivity to less than 1 K, while increasing the equator-to-pole amplification of the surface air temperature response from a factor of about three to a factor of four. However, it is concluded that whatever changes in future GCM response might occur as a result of new parametrizations of subgrid-scale processes, they are exceedingly unlikely to produce a climate sensitivity to a CO₂ doubling of less than 1 K even if there is a strong downward shift in the water vapor distribution as climate warms. Received: 23 February 1998 / Accepted: 1 November 1999     

CO2 threshold for millennial-scale oscillations in the climate system: implications for global warming scenarios

We present several equilibrium runs under varying atmospheric CO₂ concentrations using the University of Victoria Earth System Climate Model (UVic ESCM). The model shows two very different responses: for CO₂ concentrations of 400 ppm or lower, the system evolves into an equilibrium state. For CO₂ concentrations of 440 ppm or higher, the system starts oscillating between a state with vigorous deep water formation in the Southern Ocean and a state with no deep water formation in the Southern Ocean. The flushing events result in a rapid increase in atmospheric temperatures, degassing of CO₂ and therefore an increase in atmospheric CO₂ concentrations, and a reduction of sea ice cover in the Southern Ocean. They also cool the deep ocean worldwide. After the flush, the deep ocean warms slowly again and CO₂ is taken up by the ocean until the stratification becomes unstable again at high latitudes thousands of years later. The existence of a threshold in CO₂ concentration which places the UVic ESCM in either an oscillating or non-oscillating state makes our results intriguing. If the UVic ESCM captures a mechanism that is present and important in the real climate system, the consequences would comprise a rapid increase in atmospheric carbon dioxide concentrations of several tens of ppm, an increase in global surface temperature of the order of 1–2°C, local temperature changes of the order of 6°C and a profound change in ocean stratification, deep water temperature and sea ice cover.     

The temporal trend of stratospheric carbonyl sulfide

Using a database of spectra collected with an airborne infrared spectrometer between 1978 and 2005, the longest record of this type, we have searched for a temporal trend in the stratospheric OCS amount. The total column above 200 hPa, in latitudes from 30° to 60°N, shows a change of about 0.77 ± 0.80% per year relative to the 2010 value which is 1.34 × 10¹⁵ molecules cm⁻²; thus not a significant change. Observations are made from the base of the stratosphere and are uniquely suited to determining the stratospheric OCS abundance.     

Atmospheric inorganic nitrogen in marine aerosol and precipitation and its deposition to the North and South Pacific Oceans

Aerosol and rain samples were collected between 48°N and 55°S during the KH-08-2 and MR08-06 cruises conducted over the North and South Pacific Ocean in 2008 and 2009, to estimate dry and wet deposition fluxes of atmospheric inorganic nitrogen (N). Inorganic N in aerosols was composed of ~68% NH₄⁺ and ~32% NO₃^– (median values for all data), with ~81% and ~45% of each species being present on fine mode aerosol, respectively. Concentrations of NH₄⁺ and NO₃⁻ in rainwater ranged from 1.7–55 μmol L⁻¹ and 0.16–18 μmol L⁻¹, respectively, accounting for ~87% by NH₄⁺ and ~13% by NO₃⁻ of total inorganic N (median values for all data). A significant correlation (r = 0.74, p < 0.05, n = 10) between NH₄⁺ and methanesulfonic acid (MSA) was found in rainwater samples collected over the South Pacific, whereas no significant correlations were found between NH₄⁺ and MSA in rainwater collected over the subarctic (r = 0.42, p > 0.1, n = 6) and subtropical (r = 0.33, p > 0.5, n = 6) western North Pacific, suggesting that emissions of ammonia (NH₃) by marine biological activity from the ocean could become a significant source of NH₄⁺ over the South Pacific. While NO₃⁻ was the dominant inorganic N species in dry deposition, inorganic N supplied to surface waters by wet deposition was predominantly by NH₄⁺ (42–99% of the wet deposition fluxes for total inorganic N). We estimated mean total (dry + wet) deposition fluxes of atmospheric total inorganic N in the Pacific Ocean to be 32–64 μmol m⁻² d⁻¹, with 66–99% of this by wet deposition, indicating that wet deposition plays a more important role in the supply of atmospheric inorganic N than dry deposition.     

The relationship between lightning activity and surface wet bulb temperature and its variation with latitude in Australia

Summary Convective Available Potential Energy (CAPE) is the driving force for thunderstorm development. CAPE is closely controlled by wet bulb temperature. The lightning activity measured by a network of ten lightning flash counters widely distributed across continental Australia was studied as a function of wet bulb temperature. At each of the stations, the monthly total of lightning ground flashes, N, increased sharply with the increase of the monthly mean daily maximum wet bulb temperature, T_w, max. The dependence was strongest in the tropics and became less pronounced at temperate latitudes. In Darwin (latitude 12° S), the lightning ground flash activity increased by over three orders of magnitude over a 7 °C range of T_w, max. The corresponding increases for Coffs Harbour (latitude 30° S) and for Melbourne (latitude 38° S) were about one and a half orders of magnitude and about half an order of magnitude, respectively, each over a 10 °C range of T_w, max. Power law approximations were derived for each of the ten stations and showed that the logarithm of N was directly proportional to the power, P, of T_w, max. The value of P showed a sharp exponential decrease with increasing latitude away from the equator.     

Diurnal variation of atmospheric CO<Subscript>2</Subscript> concentration and δ<Superscript>13</Superscript>C in an urban atmosphere during winter—role of the Nocturnal Boundary Layer

The paper presents the importance of the Nocturnal Boundary Layer in driving the diurnal variability of the atmospheric CO₂ mixing ratio and the carbon isotope ratio at ground level from an urban station in India. Our observations are the first of their kind from this region. The atmospheric CO₂ mixing ratio and the carbon isotopic ratio were measured for both the morning (05:30–07:30 IST) and afternoon time (16:00–18:00 IST) air samples at 5 m above ground level in Bangalore city, Karnataka State (12° 58′ N, 77° 38′ E, masl = 920 m) for a 10 day period during the winter of 2008. We observed a change of ~7% the in CO₂ mixing ratio between the morning and afternoon time air samples. A stable isotope analysis of CO₂ from morning samples showed a depletion in the carbon isotope ratio by ~2‰ compared to the afternoon samples. Along with the ground-based measurement of air samples, data of radiosonde measurements were also obtained from the Indian Meteorological Department to identify the vertical atmospheric structure at different time in a day. We proposed the presence or absence of the NBL as a controlling factor for the observed variability in the mixing ratio as well as its isotopic composition. Here we used the Keeling model approach to find out the carbon isotope ratio for the local sources. The local sources have further been characterized as anthropogenic and biological respiration (in %) using a two-component mixing model. We also used a vertical mixing model based on the concept of the mixing of isotopically depleted (carbon isotope) “polluted air” (PA) with isotopically enriched “free atmospheric air” (FA) above. Using this modeling approach, the contribution of FA at ground level is being estimated for both the morning and afternoon time air samples.     

Stabilization of thermohaline circulation by wind-driven and vertical diffusive salt transport

 The stability of the thermohaline circulation is investigated using an ocean general circulation model coupled to a simple atmospheric model. The atmospheric model is so developed that it represents the wind stress and the freshwater flux more realistically than existing energy balance models. The coupled model can reproduce the realistic deep ocean circulation without any flux adjustment. Effects of the wind stress and the vertical diffusion on the thermohaline circulation are studied by conducting various experiments with the coupled model. The Ekman upwelling between 60^∘N and 90^∘N brings up salt to the sea surface, while the compensation flow of the Ekman transport and the wind-driven gyre circulation between 30^∘N and 60^∘N carry salt horizontally to the high latitudes. By carrying out experiments where the wind stress is completely or partly removed, it is demonstrated that either of the vertical or the horizontal salt transport prevents the halocline formation at high latitudes and maintains the thermohaline circulation. For an experiment in which the vertical diffusivity is enhanced at high latitudes, it is shown that the vertical diffusion at high latitudes also prevents the halocline formation and stabilizes the thermohaline circulation. It is also shown that the value of the vertical diffusivity at high latitude affects the existence of the multiple equilibria of the thermohaline circulation. Received: 26 April 2000 / Accepted: 10 January 2001     

Solar Activity and Algal-bloom Occurrences in the Northern Adriatic Sea: Geomagnetic Connection

Summary The high-speed particle flux (solar wind) escaping from the Sun controls the geomagnetic activity at middle latitudes. The latter is found to be negatively correlated to the difference of atmospheric pressure between January and April averaged out in the area of the Northern Adriatic. This difference is again related to the water volume flowing from the South into the Northern Adriatic Sea and is a necessary (though not sufficient) condition for the occurrence of strong algal-blooms in summer. A physical model involving geomagnetic activity, mean atmospheric pressured difference between latitude 35 °N and 55 °N in the European area and atmospheric pressure difference from winter to spring in the Northern Adriatic basin is proposed. The possibility of predicting the long-term variations of geomagnetic activity allows one to obtain long-term predictions of winter minus spring pressure and therefore indications of the risk of strong summer-time algal-bloom episodes. Received March 29, 1996 Revised February 14, 1997     

Measurements of surface ozone at semi-arid site Anantapur (14.62°N, 77.65°E, 331 m asl) in India

In the present study, an attempt has been made to examine the governing photochemical processes of surface ozone (O₃) formation in rural site. For this purpose, measurements of surface ozone and selected meteorological parameters have been made at Anantapur (14.62°N, 77.65°E, 331 m asl), a semi-arid zone in India from January 2002 to December 2003. The annual average diurnal variation of O₃ shows maximum concentration 46 ppbv at noon and minimum 25 ppbv in the morning with 1σ standard deviation. The average seasonal variation of ozone mixing ratios are observed to be maximum (about 60 ppbv) during summer and minimum (about 22 ppbv) in the monsoon period. The monthly daytime and nighttime average surface ozone concentration shows a maximum (55 ± 7 ppbv; 37 ± 7.3 ppbv) in March and minimum (28 ± 3.4 ppbv; 22 ± 2.3 ppbv) in August during the study period. The monthly average high (low) O₃ 48.9 ± 7.7 ppbv (26.2 ± 3.5 ppbv) observed at noon in March (August) is due to the possible increase in precursor gas concentration by anthropogenic activity and the influence of meteorological parameters. The rate of increase of surface ozone is high (1.52 ppbv/h) in March and lower (0.40 ppbv/h) in July. The average rate of increase of O₃ from midnight to midday is 1 ppbv/h. Surface temperature is highest (43–44°C) during March and April months leading to higher photochemical production. On the other hand, relative humidity, which is higher during the rainy season, shows negative correlation with temperature and ozone mixing ratio. It can be seen that among the two parameters are measured, correlation of surface ozone with wind speed is better (R ²=0.84) in compare with relative humidity (R ²=0.66).     

Sea-level pressure variability around Antarctica since A.D. 1750 inferred from subantarctic tree-ring records

 A tree-ring chronology network recently developed from the subantarctic forests provides an opportunity to study long-term climatic variability at higher latitudes in the Southern Hemisphere. Fifty long (1911–1985), homogeneous records of monthly mean sea-level pressure (MSLP) from the southern latitudes (15–65^°S) were intercorrelated on a seasonal basis to establish the most consistent, long-term Trans-Polar teleconnections during this century. Variations in summer MSLP between the South America-Antarctic Peninsula and the New Zealand sectors of the Southern Ocean are significantly correlated in a negative sense (r=−0.53, P<0.001). Climatically sensitive chronologies from Tierra del Fuego (54–55^°) and New Zealand (39–47^°) were used to develop verifiable reconstructions of summer (November to February) MSLP for both sectors of the Southern Ocean. These reconstructions, which explain between 37 and 43% of the instrumentally recorded pressure variance, indicate that inverse trends in MSLP from diametrically opposite sides of Antarctica have prevailed during the past two centuries. However, the strength of this relationship varies over time. Differences in normalized MSLP between the New Zealand and the South America-Antarctic Peninsula sectors were used to develop a Summer Trans-Polar Index (STPI), which represents an index of sea-level pressure wavenumber one in the Southern Hemisphere higher latitudes. Tree-ring based reconstructions of STPI show significant differences in large-scale atmospheric circulation between the nineteenth and the twentieth centuries. Predominantly-negative STPI values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the New Zealand sector during the 1800s. In contrast, cyclonic activity appears to have been stronger in the mid-twentieth than previously for the South American sector of the Southern Ocean. Recent variations in MSLP in both regions are seen as part of the long-term dynamics of the atmosphere connecting opposite sides of Antarctica. A detailed analysis of the MSLP and STPI reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3.3–3.6 y. Cross spectral analysis between the STPI reconstruction and the Southern Oscillation Index suggests that teleconnections between the tropical ocean and extra-tropical MSLP variations may be influencing climate fluctuations at southern latitudes. Received: 18 December 1996/Accepted: 10 January 1997     

North Sea-Caspian Pattern (NCP) – an upper level atmospheric teleconnection affecting the Eastern Mediterranean: Identification and definition

Summary An upper level atmospheric teleconnection between grid points: 0°, 55° N; 10° E, 55° N (North Sea) and 50° E, 45° N; 60° E, 45° N (northern Caspian) was identified. This teleconnection, referred as the North Sea-Caspian Pattern (NCP) is evident at the 500 hPa level. The NCP is more pronounced during winter and the transitional seasons. An index (NCPI) measures the geopotential heights differences between the two poles of the NCP. Time series of the NCPI are presented and analysed. Except for September, no significant temporal trends were found. Negative and positive phases of the NCP (NCP(−) and NCP(+), respectively) were defined using standardized scores. A classification of all months into NCP(−), NCP(+) or normal conditions during the analysis period (1958–1998) was prepared and analysed. No significant correlation was found between the NCPI and the NAO index. The anomalous circulation during either NCP(−) or NCP(+) conditions is defined and its possible impact on the regional climate is discussed. Preliminary results show below normal temperatures and above normal precipitation in the Balkans and the Middle East during NCP(+), and the opposite for NCP(−). Received March 8, 2001 Revised July 3, 2001     

A probabilistic calibration of climate sensitivity and terrestrial carbon change in GENIE-1

In order to investigate Last Glacial Maximum and future climate, we “precalibrate” the intermediate complexity model GENIE-1 by applying a rejection sampling approach to deterministic emulations of the model. We develop ~1,000 parameter sets which reproduce the main features of modern climate, but not precise observations. This allows a wide range of large-scale feedback response strengths which generally encompass the range of GCM behaviour. We build a deterministic emulator of climate sensitivity and quantify the contributions of atmospheric (±0.93°C, 1σ) vegetation (±0.32°C), ocean (±0.24°C) and sea–ice (±0.14°C) parameterisations to the total uncertainty. We then perform an LGM-constrained Bayesian calibration, incorporating data-driven priors and formally accounting for structural error. We estimate climate sensitivity as likely (66% confidence) to lie in the range 2.6–4.4°C, with a peak probability at 3.6°C. We estimate LGM cooling likely to lie in the range 5.3–7.5°C, with a peak probability at 6.2°C. In addition to estimates of global temperature change, we apply our ensembles to derive LGM and 2xCO₂ probability distributions for land carbon storage, Atlantic overturning and sea–ice coverage. Notably, under 2xCO₂ we calculate a probability of 37% that equilibrium terrestrial carbon storage is reduced from modern values, so the land sink has become a net source of atmospheric CO₂.     

Extreme events,trends, and variability in Northern Hemisphere lake-ice phenology (1855–2005)

Often extreme events, more than changes in mean conditions, have the greatest impact on the environment and human well-being. Here we examine changes in the occurrence of extremes in the timing of the annual formation and disappearance of lake ice in the Northern Hemisphere. Both changes in the mean condition and in variability around the mean condition can alter the probability of extreme events. Using long-term ice phenology data covering two periods 1855–6 to 2004–5 and 1905–6 to 2004–5 for a total of 75 lakes, we examined patterns in long-term trends and variability in the context of understanding the occurrence of extreme events. We also examined patterns in trends for a 30-year subset (1975–6 to 2004–5) of the 100-year data set. Trends for ice variables in the recent 30-year period were steeper than those in the 100- and 150-year periods, and trends in the 150-year period were steeper than in the 100-year period. Ranges of rates of change (days per decade) among time periods based on linear regression were 0.3−1.6 later for freeze, 0.5−1.9 earlier for breakup, and 0.7−4.3 shorter for duration. Mostly, standard deviation did not change, or it decreased in the 150-year and 100-year periods. During the recent 50-year period, standard deviation calculated in 10-year windows increased for all ice measures. For the 150-year and 100-year periods changes in the mean ice dates rather than changes in variability most strongly influenced the significant increases in the frequency of extreme lake ice events associated with warmer conditions and decreases in the frequency of extreme events associated with cooler conditions.     

Intraseasonal variability of the Tropical Easterly Jet

Summary By analyzing 12-year (1979–1990) 200 hPa wind data from National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis, we demonstrate that the intraseasonal time scale (30–60 days) variability of the Tropical Easterly Jet (TEJ) reported in individual case studies occurs during most years. In the entrance region (east of ∼70° E), axis of the TEJ at 200 hPa is found along the near equatorial latitudes during monsoon onset/monsoon revivals and propagates northward as the monsoon advances over India. This axis is found along ∼5° N and ∼15° N during active monsoon and break monsoon conditions respectively. Examination of the European Centre for Medium Range Weather Forecasts reanalysis wind data also confirms the northward propagation of the TEJ on intraseasonal time scales. During the intraseasonal northward propagations, axis of the TEJ is found about 10°–15° latitudes south of the well-known intraseasonally northward propagating monsoon convective belts. Because of this 10°–15° displacement, axis of the TEJ arrives over a location about two weeks after the arrival of the monsoon convection. Systematic shifting of the locations by convection, low level monsoon flow and TEJ in a collective way during different phases of the monsoon suggests that they all may be related.     

Effect of tropospheric temperature change on the zonal mean circulation and SH winter extratropical cyclones

This study aims to understand the mechanisms which cause an overall reduction of SH extratropical cyclone activity with a slight increase in the high latitudes in a warmer climate simulated in general circulation models (GCMs) with increasing CO₂. For this purpose, we conducted idealized model experiments by forcing warm temperature anomalies to the areas where climate change models exhibit local maximum warming—the tropics in the upper troposphere and the polar regions in the lower troposphere—simultaneously and separately. The Melbourne University atmospheric GCM (R21) coupled with prescribed SST was utilized for the experiments. Our results demonstrate that the reduction of SH extratropical cyclone frequency and depth in the midlatitudes but the slight increase in the high latitudes suggested in climate change models result essentially from the tropical upper tropospheric warming. With this tropical warming, the enhanced static stability which decreases baroclinicity in the low and midlatitudes turns out to be a major contributor to the decrease of cyclone activity equatorward of 45°S whereas the increased meridional temperature gradient in the high latitudes seems an important mechanism for the increase of cyclone activity over 50°–60°S.     

Numerical study of the oxidation process of dimethylsulfide in the marine atmosphere

A box model, involving simple heterogeneous reaction processes associated with the production of non-sea-salt sulfate (nss-SO ₄ ^2– ) particles, is used to investigate the oxidation processes of dimethylsulfide (DMS or CH₃SCH₃) in the marine atmosphere. The model is applied to chemical reactions in the atmospheric surface mixing layer, at intervals of 15 degrees latitude between 60° N and 60° S. Given that the addition reaction of the hydroxyl radical (OH) to the sulfur atom in the DMS molecule is faster at lower temperature than at higher temperature and that it is the predominant pathway for the production of methanesulfonic acid (MSA or CH₃SO₃H), the results can well explain both the increasing tendency of the molar ratio of MSA to nss-SO ₄ ^2– toward higher latitudes and the uniform distribution with latitude of sulfur dioxide (SO₂). The predicted production rate of MSA increases with increasing latitude due to the elevated rate constant of the addition reaction at lower temperature. Since latitudinal distributions of OH concentration and DMS reaction rate with OH are opposite, a uniform production rate of SO₂ is realized over the globe. The primary sink of DMS in unpolluted air is caused by the reaction with OH. Reaction of DMS with the nitrate radical (NO₃) also reduces DMS concentration but it is less important compared with that of OH. Concentrations of SO₂, MSA, and nss-SO ₄ ^2– are almost independent of NO _x concentration and radiation field. If dimethylsulfoxide (DMSO or CH₃S(O)CH₃) is produced by the addition reaction and further converted to sulfuric acid (H₂SO₄) in an aqueous solution of cloud droplets, the oxidation process of DMSO might be important for the production of aerosol particles containing nss-SO ₄ ^2– at high latitudes.     

The acid catalyzed nitration of methanol: formation of methyl nitrate via aerosol chemistry

The aqueous phase acid-catalyzed reaction of methanol (CH₃OH) with nitric acid (HNO₃) to yield methyl nitrate (CH₃ONO₂) under atmospheric conditions has been investigated using gas-phase infrared spectroscopy. Reactions were conducted in aqueous sulfuric acid solutions (50.5–63.6 wt.%) with [CH₃OH] = 0.00005–0.005 M and [HNO₃] = 0.02–0.21 M, at 278.2–328.6 K. Methyl nitrate production rates increased linearly with CH₃OH and HNO₃ concentrations and exponentially with sulfuric acid weight percent within the regime studied. Rates increased linearly with nitronium ion concentration, indicating that the reaction involves as the nitrating agent under these conditions. At 298 K, the rate of methyl nitrate production can be calculated from k _obs [CH₃OH][HNO₃], where k _obs  = 2.337 × 10⁻¹³(exp(0.3198*wt.% H₂SO₄)) when the solubility of CH₃ONO₂ in acidic solution is approximated by H* for pure water. The temperature dependence of the rate coefficient is related to solution composition, with activation energies of 59 and 49 kJ/mol at 51.1 and 63.6 wt.% H₂SO₄, respectively, when k is calculated from rate. The temperature dependence has also been parameterized for application to the atmosphere, but the small quantities of present in aerosol particles will result in methyl nitrate production rates too small to be of significance under most atmospheric conditions. An erratum to this article can be found at