Yu. M. Timofeev

NO2 content variations near St. Petersburg as inferred from ground-based and satellite measurements of scattered solar radiation

An automatic spectral complex developed at the Institute of Physics, St. Petersburg State University, is described. This complex is used for regular ground-based spectroscopic measurements of the total NO2 content in the vertical column of the atmosphere during the twilight and daylight hours of the day near St. Petersburg (Petrodvorets). In 2004–2006, a number of ground-based twilight measurements of the total NO2 content were obtained near St. Petersburg, and variations in the NO2 content in the troposphere were estimated from the results of daytime ground-based measurements. An example of the spatial annual mean distribution of the NO2 content (central and northern Europe, northwestern Russia) based on the data of satellite measurements over the period 2003–2005 is presented. This example demonstrates the main sources of anthropogenic pollution. An increase in the mean annual contents of tropospheric NO2 near Moscow and St. Petersburg is preliminarily estimated for the entire period of satellite observations with the GOME instrument at about 30–40% over ten years.

Ground-based measurements of total ozone content by the infrared method

To interpret the ground-based measurements of the spectra of direct solar infrared radiation with the help of a Brucker Fourier-spectrometer, a technique for determining the total ozone content (TOC) was developed and implemented. The TOC was determined using six spectral intervals of an ozone-absorption band of 9.6 μm and the shortwave panel of a carbon-dioxide-absorption band of 15 μm, where the impact of other atmospheric parameters on the measured solar radiation was reduced to a minimum. The potential errors of the infrared method for determining the TOC for the chosen spectral scheme with the influence of measurement errors and vertical profiles of temperature are less than 1% for different signal-to-noise ratios and zenith angles of the sun. We analyzed 269 high-resolution (0.005–0.008 cm−1) spectra of solar infrared radiation measured in Peterhof over 52 days from March to November, 2009. The resulting values of TOC were compared with the results of independent ground-based TOC measurements in Voeikovo (Main Geophysical Observatory) using a Dobson spectrophotometer and an M-124 ozonometer, as well as with the Ozone Monitoring Instrument (OMI) satellite data. The mean errors between the results of TOC measurements with the help of the three ground-based probes constitute no more than 0.4%. The rms errors between data obtained by the Brucker spectrometer and the given satellite and ground-based probes constitute 3–4%. A comparison between different series of measurements indicated that the upper estimate for the error of TOC measurements by the Brucker spectrometer was 2.5–3% (when the possible spatial and temporal errors in measurements are disregarded). An analysis of the diurnal variations in the TOC measurements for stable atmospheric conditions yields an upper estimate of ∼3 DU (around 1%) for the random component of error in TOC measurements by the Brucker spectrometer.

Seasonal variations in the total content of hydrogen fluoride in the atmosphere

The results of ground-based measurements of the total content (TC) of hydrogen fluoride in the atmosphere in Peterhof near St. Petersburg for one year (from April 2009 through April 2010) using a Bruker IFS125 Fourier spectrometer with a high spectral resolution (0.005 cm−1) are presented. The well-known computer code SFIT2 (Zephyr-2) was used for the radiation data inversion. Random measurement errors were 1–5% and the systematic error was 5–10%. The seasonal trend of the HF TC in Peterhof is characterized by a minimum in summer and a maximum in winter through early spring and is very close to the seasonal HF TC trend obtained at the Harestua Network for the Detection of Atmospheric Composition Change (NDACC) station located at about the same latitude. A comparison of the St. Petersburg State University (SPbSU) ground-based measurements with the data of satellite HF TC measurements (with an ACE-FTS instrument) showed a good quantitative agreement of the results for the entire period of observations. According to our ground-based measurements and the satellite measurements with the ACE-FTS instrument, the mean values of the HF TC and its rms variations during the period under investigation are 1.77 × 1015 and 1.80 × 1015 cm−2 (difference 1.5%) and 21 and 18%, respectively.

Spectroscopic measurements of total CFC-11 freon in the atmosphere near St. Petersburg

On the basis of ground based measurements of the infrared spectra of solar radiation with a high spectral resolution, estimates of total CFC-11 freon content in the atmosphere near St. Petersburg in January and May 2009 have been yielded in Russia for the first time. These data are conformed to various independent measurements within the limits of spectroscopic measurement errors.

Regional space monitoring of nitrogen dioxide in the troposphere

Satellite instruments for the routine global monitoring of NO2 in the atmosphere—the Global Ozone Monitoring Experiment (GOME) on the ERS-2 satellite, the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) on the ENVISAT satellite, the Ozone Monitoring Instrument (OMI) on the AURA satellite, and the GOME-2 on the MetOp satellite—are briefly described. It is shown that the error of measuring the NO2 total column amount (∼10% for the background conditions in the troposphere) substantially increases in regions subject to anthropogenic pollution. Examples of practically using multiyear satellite measurements for the regional monitoring of NO2 in the troposphere are presented, including mapping the tropospheric NO2 in Russia, identifying the weekly and annual cycles in tropospheric NO2 variations for megalopolises (St. Petersburg, Moscow, Paris), and estimating the long-term linear trend in 1995–2007.

Ground-based measurements of total column of hydrogen chloride in the atmosphere near St. Petersburg

We present ground-based spectroscopic measurements of the total hydrogen chloride in the atmosphere of Peterhof near St. Petersburg from April 2009 to March 2012. The well-known computer code SFIT-2 (Zephyr-2) was used to interpret the spectra of the solar IR radiation. The random and systematic errors of total column (TC) HCl measurements did not exceed 3.8 and 4.5%. The seasonal behavior of TC HCl in Peterhof is characterized by the presence of a maximum in March–April and a minimum in October–November. There are also extremely small TC HCl values in January–February. The time behavior obtained for Peterhof agrees well with data from nearest stations in the NDACC international network. The ground-based measurements of the TC HCl were compared with satellite measurements with the help of ACE-FTS and MLS instruments. The direct comparisons of coincident (within a day) and collocated (within 500 km) satellite and ground-based measurements showed a correspondence of results within their total errors.

Comparisons of satellite (GOSAT) and ground-based spectroscopic measurements of CO2 content near St. Petersburg

The column-average mole fractions of atmospheric carbon dioxide measured with ground-based Fourier-transform spectroscopy at the Peterhof station of St. Petersburg State University (59.9° N, 29.8° E) in 2009–2011 are compared with similar data obtained with the Japanese GOSAT satellite. The comparison shows that the average mole fractions of CO2 from satellite data version V01.xx are lower by −9.8 ± 3 ppm than the corresponding values obtained from the ground-based measurements. For the GOSAT data version V02.xx, this difference is −4.7 ± 2.6 ppm on the average. Some overestimation of CO2 values in measurements near St. Petersburg in comparison with the ground-based TCCON network data has been revealed indirectly, the causes of which require further explanation.

Variations in the column-average dry-air mole fractions of CO2 in the vicinity of St. Petersburg

The results obtained from ground-based spectroscopic measurements of column-average dry-air mole fractions of CO2 in the atmosphere over the St. Petersburg region are given for the period April 2009–October 2011 (∼900 measurement runs, 151 measurement days). These results show significant variations in the CO2 mixing ratio in the atmosphere over the St. Petersburg region. The minimum value of this mixing ratio (373.1 ppm) was observed on April 27, 2011, and its maximum value (420.8 ppm) was observed on February 10, 2010. The typical seasonal behavior of the CO2 mixing ratio with its summer minimum was observed in 2009. In July 2010 and 2011, the values of the CO2 mixing ratio increased apparently due to high air temperatures. In 2010 an additional contribution to this increase in the CO2 mixing ratio could have been made by strong natural fires.

Evaluation of ozone content in different atmospheric layers using ground-based Fourier transform spectrometry

For the first time in Russia, using ground-based measurements of direct solar infrared radiation, we derived data on ozone content in different layers of the atmosphere. The measurements were conducted with the help of a Bruker IFS-125HR Fourier spectrometer in 2009–2012 in Petergof, which is 30 km west of the center of St. Petersburg. The errors in determining the ozone content by this method in the troposphere (0–12 km), in the stratosphere (12–50 km), in the layers of 10–20 and 20–50 km, and in the layers of 12–18, 18–25, and 25–50 km were ~4, 3, 3–5, and 4–7% (taking into account the instrumental and methodological errors, as well as the errors in specifying the temperature profile), respectively. The seasonal variation of tropospheric ozone content in the layer of 12–18 km is characterized by a clearly expressed maximum in March and a minimum in November, with amplitudes of 30 and 40%, respectively. For the layer of 18–25 km, the maximum and minimum are reached in the winter-spring period and late summer, respectively; the amplitude of the seasonal variation is ~20%. The amplitude of the annual variation in ozone content in the layer of 25–50 km is around 30%, with a maximum close to the summer solstice and a minimum close to the winter solstice. Over the three years of observations, the growth in the ozone content in this layer was ~10% per year of its value averaged over the time period. Comparisons of ground-based measurements with satellite measurements (by the IASI instrument) of tropospheric ozone revealed a discrepancy of (3.4 ± 17)% for both ensembles. The correlation between the two ensembles is 0.76–0.84 (depending on the season). Comparisons between ground-based and satellite measurements (by the MLS instrument) of stratospheric ozone revealed no systematic discrepancies of the two ensembles. The rms errors were 13, 6, and 5% for the layers of 10–20, 20–50, and 10–50 km, respectively; the coefficients of correlations between the two types of measurements were 0.82–0.94.

Stratospheric NO2 content according to data from ground-based measurements of solar IR radiation

Atmospheric NO2 content data obtained from regular ground-based measurements of solar IR radiation in the St. Petersburg region using a spectrometer with a high spectral resolution are analyzed. The absorption spectra of the NO2 multiplet in the vicinity of ∼2915 cm−1 allow one to obtain data on variations in the stratospheric total content of NO2 in 2009–2011. The accuracy of these data is estimated from their comparison with data obtained from independent ground-based and satellite measurements. The parameters of the seasonal cycle of the stratospheric content of NO2 are estimated. The body of data accumulated during these measurements in the IR region made it possible to isolate the component of a daytime photochemical increase in the stratospheric content of NO2 and estimate its rate.