Remote Environmental Monitoring of Major Industrial Centres

Today, perhaps the most popular term in specialist and popular-science environmental literature is “monitoring.” It generally means observation, assessment, and prediction of environmental conditions in relation to human economic activity. The term often denotes various systematic survey activities directed at environmental investigation targets: major industrial centres, mining enterprises, product pipelines, forests, fields, and rivers…

Monitoring takes different forms…

The concept of environmental monitoring emerged in the mid-1970s and became widespread both in our country and abroad. At present, three main types of environmental monitoring system are being developed worldwide:

• systems based on permanent integrated monitoring stations, currently adopted in the West and, in our view, extremely costly, particularly when funding is allocated on a residual basis, because they require a dense network of expensive sensors, a data-transmission system and a single powerful processing centre;
• a network of integrated mobile ground laboratories, used in Russia and the CIS countries, which essentially permits only selective monitoring, both in the range of pollutants and in the area covered;
• remote monitoring based on integrated aerial surveys (enabling information to be obtained rapidly over large areas, but not permitting detection of emergency situations);

Thus, given the specific economic conditions, the most effective approach appears to be a combination of the first and third forms of environmental monitoring, in which continuous observations by a relatively sparse network of fixed stations are accompanied by regular, preferably seasonal, integrated remote-sensing surveys. Aerial surveys have no alternative in productivity and minimizing cost per unit area while recording a broad range of parameters. In this case, monitoring generally involves regular seasonal area-wide aerial surveys of industrial centres and urban agglomerations at scales of 1:10000–1:25000.

Components of the remote environmental monitoring system.

GNPP Aerogeofizika’s development of a remote environmental monitoring system is primarily associated with the large volume of airborne gamma-ray spectrometric surveys we conducted over territories contaminated by radiation after the Chernobyl nuclear power plant accident. It was then that the McPhar II system, previously used to map undeveloped territories for geological exploration, was deployed in densely populated areas, including cities. This prompted the idea of supplementing the airborne system with instrumentation for recording a broader range of parameters characterizing the condition of the area under investigation.

Analysis of the range of instruments then available in the country and suitable for this purpose, together with methodological studies of their potential use alongside the existing system, led us to conclude that it was possible in principle to assess the state of the air environment, specifically the gaseous components and atmospheric aerosols primarily responsible for its pollution.

Among the various gas analysers, most of which determine gas concentrations at the location of the instrument or its air intake, we selected open-path instruments as being more consistent with the concept of remote sensing. N. S. Pugachev of the Institute of Atmospheric Physics, Russian Academy of Sciences, made a major contribution to developing methods for airborne use of such systems, followed by A. A. Liberman and M. L. Gurari (VNIIOFI), who undertook a series of developments to create a family of correlation spectrophotometers—open-path NO₂ and SO₂ analysers. We selected these instruments for their reliability, high sensitivity, immunity to interference and correct operation. The jointly developed airborne gas survey method using scattered solar radiation determines the concentrations of the gases being measured within the instruments’ optical field-of-view cone (3 ) below flight altitude, thus specifically recording pollution in the near-surface atmosphere.

At the same time, in collaboration with specialists from IKI and the Karpov NIVKhI, we developed a system for collecting atmospheric aerosol samples on ultrapure Petryanov filters (the USA-1 sampler), developed a sampling procedure for areal airborne surveys, and established requirements for sample preparation and subsequent laboratory chemical analysis.

The first experimental and methodological airborne gas and aerosol surveys were carried out in Moscow in autumn 1991. An airborne gamma-ray spectrometric survey of the city was conducted at the same time. These were followed by surveys in summer 1992 and winter 1993, making it possible to speak of seasonal monitoring of the capital. In 1993, integrated surveys covered the Norilsk industrial zone, including the city itself, the industrial complex and nearby deposits under development. In 1995, integrated surveys of Tula in two seasons (January and August), including airborne thermal infrared imaging, were commissioned by the city administration. In March 1996, Moskompriroda commissioned a survey of Moscow using the full suite of methods, including airborne infrared imaging. A complete cycle of seasonal monitoring surveys and subsequent integrated processing is planned.

The airborne geophysical system for remote environmental monitoring developed at GNPP Aerogeofizika and used on an operational scale comprises airborne gas surveys to determine NO_2, SO_2, CH₄ concentrations in the near-surface atmosphere; airborne aerosol surveys to determine concentrations of pollutant elements in atmospheric aerosols; and airborne gamma-ray spectrometry to map the nature and extent of contamination of the surveyed area by natural and artificial radionuclides.

Integrated environmental airborne geophysical surveys are conducted using a Mi-8T helicopter along a network of straight flight lines spaced 100–250 m apart. The survey altitude of 150 m is determined by the range between the minimum permitted altitude and the maximum allowed by the methodology for large-scale aerosol surveys. Surveys are carried out under relatively stable meteorological conditions, i.e. winds not exceeding 5 m/s and humidity up to 90%.

A GPS+GLONASS satellite navigation system (our own development based on the ASHTECH GG-24 receiver) is used for flight-line navigation and horizontal positioning of survey results.

All types of airborne surveys performed are licensed by Roskartografiya and the Ministry of Natural Resources.

Airborne gas surveys use high-sensitivity digital open-path analysers for NO₂, SO₂ and CH₄ (with scope to expand this range). The instruments provide rapid measurement of the integrated gas concentration along a specified path (direction) and determine the mean concentration over its calculated or specified length. The measurement error does not exceed 15%.

The resulting concentration maps of the gaseous components analysed illustrate in detail the integrated levels of air pollution during the airborne survey.

Airborne aerosol surveys. The atmospheric aerosol sampling procedure is designed so that one sample characterizes a survey-area element measuring from 2*2 to 1*1 km. A sample comprises one to four filters, depending on the number of flight lines crossing that area element; a single sample includes filters collected on different days along different flight lines (a sparse flight-line network covers the entire city in one survey day). This procedure has virtually eliminated the possibility of introducing systematic error into the measurements. Each filter is exposed for approximately 60 seconds, which, given the average pollution level of the urban atmosphere, yields a filter loading ranging from hundreds and tens (K, Al, Fe, Pb) to hundredths (Co, Mn, etc.) of µg/sample. Filters are changed automatically during flight.

Aerosols collected on the filters are analysed in the laboratory by atomic absorption and inductively coupled plasma atomic emission methods to determine concentrations of up to 60 chemical elements. Background filters (2–3% of the total) are also analysed in the laboratory for concentrations of pollutant elements.

Clients receive a set of maps showing the distribution of pollutant elements in atmospheric aerosols and the total aerosol component.

Airborne gamma-ray spectrometric surveys follow a standard procedure using a 512-channel digital spectrometer with 48 L EXPLORANIUM Polyscin NaI(Tl) detectors, providing an energy resolution at the 0.662 MeV line (Cs^{137) of 9%.}

The survey results are used to map the distribution of natural (K, U, Th, Rn²²²) and artificial (Cs¹³⁷) radionuclides.

The unique equipment and original data-processing technology developed at Aerogeofizika allow airborne gamma-ray spectrometric data to be used to map the distribution, across the study area, of the local component of free radon that delineates geodynamic zones (zones of present-day faults). Such information is valuable in engineering site investigations and in identifying priority locations for sanitary and epidemiological surveillance of basements in existing buildings.

Although all types of airborne surveys can be conducted separately, their combined, integrated use provides the greatest benefit while minimizing costs (aviation is paid for once). Depending on the specific tasks, the suite may also be supplemented, for example, by airborne thermal infrared imaging and other airborne geophysical methods.

Integrated airborne remote-sensing survey materials are supplied to clients on paper and electronically in any required format, including ready-to-use GIS layers.

What next?

Ultimately, the purpose of remote environmental monitoring is to provide a formal basis for management decisions aimed at managing the population’s quality of life. Decision-makers must have access to a wide variety of data on the state of the environment (land, water, air…), spatially referenced information characterizing the population’s quality of life, and so on. Clearly, management decisions imply establishing a one-to-one relationship between the nature and degree of contamination of an area and the characteristics of the population’s quality of life. For a number of objective reasons, however, this is not straightforward. First, environmental conditions are determined by the presence of a very large number of pollutants; we can currently determine concentrations of up to 60 elements in airborne aerosols alone, as well as a number of gaseous components. Identifying precisely which of these, and in which combinations, have a decisive impact on public health appears extremely difficult. Second, as noted above, the air environment is highly dynamic with respect to the impurities it contains. Pollutants from different sources can be transported by wind, react to form new compounds, become bound, and be removed by water or soil. Third, landscape and geological conditions significantly influence pollutant composition and persistence, promoting the accumulation of some chemical elements and compounds and the removal of others. Fourth, the population’s quality of life is determined not only, and not so much, by the nature and degree of environmental pollution, but to a considerable extent by social factors (even the quality of local vodka is known to affect life expectancy…).

A way out of this difficult situation may be to use specialized mathematical methods and tools for targeted data processing that facilitate the task. The very structure of the problems calls for probabilistic and statistical analysis. We developed a complete workflow for such analysis and partially tested it in targeted processing of the integrated environmental airborne survey data for Tula from the 1995–96 seasons, together with indicators of the city population’s quality of life (three years of civil registry statistics). The main feature of this workflow is a sequence of analytical steps (procedures), each designed to address a specific group of tasks and bring us closer to the ultimate objective.

The first and principal step reduces the dimensionality of the original environmental data, preferably without loss of information. This operation can provide landscape and geological regionalization of the study area and identify the most persistent combinations of major pollutants and their distribution within the city. In our view, principal component analysis is the most convenient tool for this stage.

In some cases, landscape and geological regionalization may benefit from specialized mathematical processing of the distribution data for an individual measured component. For example, analysis of free-radon concentrations appears capable of identifying the crustal faults through which radon enters the atmosphere. Physical-field filtering algorithms are used for this purpose.

The second processing step provides an integrated analysis of quality-of-life indicators to structure them and identify combinations more strongly influenced by environmental conditions. These may include elevated incidence of particular diseases, changes in population age structure, an adverse mortality pattern by age group and cause, and so forth. Clearly, this work requires the involvement of sanitary and epidemiological surveillance services and healthcare authorities. Multivariate statistical methods, including factor analysis, are best suited to these tasks. Analytically, these algorithms are analogous to the principal component method described above.

The third step of integrated processing links the identified areas of elevated background pollution to possible sources, which in principle allows zones of responsibility for air pollution to be assigned to industrial complexes and enterprises, and establishes the nature and strength of the relationship between contamination of the area and quality-of-life indicators. Multiple correlation and regression analysis, as well as discriminant analysis, can be used here.

The work concludes with an analysis of possible alternative ways to resolve the situation. In principle, environmental damage can be assessed in physical and monetary terms through losses in the working-age population caused by elevated morbidity and mortality. Material losses can, and certainly should, be compensated by the enterprises responsible for pollution. Two courses are then possible: programmes giving priority to the installation of treatment facilities, or closure of enterprises. The latter entails an additional set of social problems and costs. Ultimately, the strategy promising the greatest benefit in the short or long term should be selected. In this respect, the problem can be successfully addressed within graph theory. The decision-maker’s task would therefore be limited to analysing possible alternative developments and selecting the most rational course, taking the full range of factors into account.

In our view, the most effective integrated solution to the full range of problems and tasks arising from survey acquisition through analysis would be a dedicated “Environment–Health” geographic information system with built-in multivariate data-processing functions, incorporating ground investigation data and municipal statistical databases. Once placed in such a GIS, remote environmental monitoring data would be used most effectively to fulfil the aspect of “monitoring” that implies forecasting the city’s environmental situation.