An early version of a grating spectrometer was developed at Cambridge University, UK and used by David Wardle in the winter of 1963 -1964 to make measurements of total column ozone during the polar night at Resolute, Canada using stellar radiation as a light source (Wardle, 1965). The instrument was later brought to the University of Toronto where subsequent versions of grating spectrometers were developed with Alan Brewer, Jim Kerr, and Tom McElroy. These instruments were used for short-term research projects that demonstrated the capability of grating spectrophotometers for measuring atmospheric ozone (Brewer and Kerr, 1973; Kerr, 1973) and nitrogen dioxide (Brewer et al., 1973). Brewer (1973) proposed that a grating spectrophotometer could be developed with the goal of supplementing the Dobson ozone spectrophotometer (Dobson, 1957) and the M-83 filter ozonometer (Gustin et al., 1985), which were the only ground-based operational instruments in use at the time. Kerr, McElroy, and Wardle moved to the Atmospheric Environment Service (AES) of Environment Canada in Downsview, Ontario in the early 1970s where the goal of developing an operational grating instrument to measure surface UV irradiance and atmospheric ozone was kept alive.
One major consideration regarding the development of a viable instrument with potential for widespread use as an operational network instrument was commercialization. It was realized that it would be necessary for the instrument to be manufactured commercially by a company capable of making specialized scientific equipment and supporting it over a long period of time. During the later part of the 1970s, the first pre-production prototype instruments (Mark I) were developed and manufactured by SED Systems of Saskatoon, Canada.
The Mark I prototype instruments were tested in operational use over a period of several months, and in field intercomparison experiments (Kerr et al., 1981; Parsons et al., 1981). Significant information regarding the calibration, stability, and reliability of the instruments was acquired during this period of operation. Much of what was learned regarding the possible improvements that were needed to address shortcomings was noted and included in the development of the production version (Mark II), which has the same optical layout and configuration as the earlier version.
The design and development of the Mark II version was carried out jointly by AES and SED Systems and focused mainly on providing fully automatic operation. Full automation of the instrument was considered to be important because the general trend for monitoring geophysical variables was evolving toward automatic measurement in order to reduce manpower and increase data volume. The Dobson spectrophotometer is not automated, and the introduction of a fully automated instrument would offer a distinct advantage.
There were several aspects that needed to be considered to enable unattended operation over different time periods over several days. The first consideration was that of data recording. The first commercial prototype provided a serial port that could output data to a printer. However, manual operations were required to align the instrument, set it up, and then initiate an observation. The requirement for manual operation was addressed by installing several stepping motors to make mechanical adjustments, which would otherwise require manual setup. About this time, personal computers were becoming available, offering a means to fulfill data recording and mechanical positioning requirements at a relatively low cost. The first "control computer" for the automated Brewer instrument was the Commodore PET, which was programmed to schedule and carry out sequences of measurements and tests. The advent of modern day personal computer technology and communication technology has significantly improved and simplified the reliability of data management tasks such as data storage, reporting, and analysis.
In the early 1980s, Brewer instruments were manufactured (by a new company called Sci-Tec Instruments Inc.) and commenced operation at Canadian sites as well as several sites operated by foreign institutes. Three Brewer instruments were established as the calibration "triad" in Downsview (Kerr et al., 1985), and the same three instruments comprise the triad today (Fioletov et al., 2005). Brewer instruments replaced the existing five Dobson instruments in the Canadian ozone-monitoring network after an overlap period of at least three years (Kerr et al., 1988). In addition, the Canadian network expanded to 12 sites beginning in the late 1980s (Kerr, 1994). Around the same time, Brewer instruments were upgraded to measure spectral UV irradiance and appropriate calibration facilities and standards were developed to allow this measurement on an absolute scale.
The Brewer instrument proved to be stable on an absolute scale over long periods of time (Kerr and McElroy, 1993). UV spectral measurement records using Brewer instruments commenced at several sites around the world in the early 1990s (Bais et al., 1994; Ito et al., 1994; Vandersee and Köhler, 1994).
During this time, two new versions of the Brewer instrument were developed: the Mark EI and the Mark IV. The Mark EI is a double monochromator, which was developed to reduce stray light that can be a problem in single monochromators. The Mark IV has a modified grating, which allows the option to measure radiation at visible wavelengths to determine atmospheric NO2, as well as the standard UV wavelengths used to determine ozone, SO2, and spectral UV irradiance. In the late 1990s, a Mark V version of the instrument was developed to measure radiation at wavelengths in visible red light (600 nm - 650 nm) where ozone is measured using the Chappuis absorption bands. This instrument can measure ozone at low sun angles (< 10° solar elevation) and is particularly suitable at high latitude locations (WMO, 2006; Tanskanen et al., 2007).
Since 1990, workshops for users of Brewer instruments have been held about every two years. These meetings have been hosted by agencies in Europe, North America, and Asia. In addition, the developers from AES (now the Meteorological Service of Canada, MSC) and manufacturers of the instrument, and the commercial companies that service and calibrate field instruments, also attend these workshops. The purpose of the workshops is to offer interested users a platform to present results and experiences from using Brewer instruments. The meetings also allow users and supporting groups the opportunity to interact with each other. The workshops are organized as a series of seminars under various topics, such as measurement type (e.g., UV, total ozone, etc.), calibration procedures, data analysis, and data archiving. Results presented at the workshops are formally published as WMO reports (e.g., WMO, 1994; WMO, 2006).
In 1996, Sci-Tec Instruments Inc. merged with Kipp and Zonen Inc. and production of the instruments was later transferred to Delft, Holland. Today only the Mark EI version of the instrument is manufactured, and the Mark II and Mark IV instruments are no longer produced. However, technical service and support is still provided for these existing instruments.
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