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The Brewer Triad and Calibrations;
the Canadian Brewer
Spectrophotometer Network
Vitali Fioletov and Stoyka Netcheva
Measurements and Analysis Research Section (ARQM)
Air Quality Research Division
Atmospheric Science and Technology Directorate
COST ACTION ES1207 EUBREWNET OPEN CONGRESS /
14th WMO-GAW BREWER USERS GROUP MEETING
State Meteorological Agency of Spain, Tenerife, Spain
24th – 28th March 2014
Network Integration
• Brewer network (7 sites with 2+ instruments and 3 sites with one instrument, 42 instruments including 10 Double Brewers) and 2 sites outside Canada
• AEROCAN sunphotometer network (20 sites)
• Ozonesondes network (8 sites)
• (new) Pandora (2 instruments)
• The Canadian Air and Precipitation Monitoring Network (CAPMoN) – operated by EC
– Particles and Related Trace Gases , 24 hour integrated filter samples. particulate Cl-, NO3-, SO4=, NH4+, Na+, K+, Ca++, Mg++, gaseous HNO3 and SO2
– Ground level Ozone Measurements , hourly averages.
– Nitrogen Measurements , gaseous NO, NO2, and NOy hourly averages.
– Size Selective Particulate Matter ,24 hour integrated samples PM2.5 , PM10 and coarse fraction mass
– Precipitation Chemistry , 24 hour integrated samples. Cl-, NO3-, SO4=, NH4+, Na+, K+, Ca++, Mg++, pH
– …
• National Air Pollution Surveillance (NAPS) – SO2, NO2, O3, PM2.5, PM10 - continuously monitored
AR
QM
Team members & support
• Stoyka Netcheva: network management
• Vitali Fioletov: science, algorithms, data analysis, QA/QC
• Tom Grajnar: network operation, calibrations, instrument maintenance
• Michael Brohart: instrument maintenance, repairs, upgrades and calibrations
• Akira Oguy: computer support, web, BPS, data processing, QA/QC
• Other ARQM staff providing support as needed
• Volodya Savastiouk - regular contracts for calibrations, instrument repairs, upgrade and maintenance of software for Brewer operation, calibrations, and diagnostics …
Support from other branches of EC (infrastructure, instrument operations, basic maintenance, and inspections) at 7 stations CANDAC occasional support at Eureka Pearl Observatory NOAA at Mauna Loa Observatory NOAA at South Pole Observatory
Network
New developments 2012-2014:
•Double Brewers at Churchill,
Goose Bay, and Stony Plain: no
more data gaps in winter
•Calibration of 4+2 Brewers at
Mauna Loa in October 2013
•The new triad of double Brewers
(#145, #187, #191) established in
October 2013
•Two new Brewer instruments
(#223 and #224) purchased in
2014
Brewers applications: Ozone change estimates Ozone changes on global scale from Dobson, Brewers and Filter Ozonometers
Deseasonalized, area-weighted total ozone deviations for 90°S–90°N, adjusted for solar, volcanic, and QBO effects. The yellow line represents the component of ozone variability due to changes in the equivalent effective stratospheric chlorine (EESC) based on a fit to data from 1964–2012 (updated from WMO (2007))
90°S–90°N
0
20
40
60
80
100
1978-1985 1986-1990 1991-1995 1996-2000 2001-2005 2006-2010
Dobson Brewer Filter
Quantity
The total number of sites reported data to the WOUDC. Stations submitted less than 100 DS observations per bin are not included
Quality
Relative number (in % of the total
number) of sites with "no issues" in the
record in 6 bins for Dobson, Brewer,
and filter instrument sites located
between 60ºS and 60ºN
Brewers applications: Brewers and others
Ground-Based total ozone data available from the World Ozone and UV Data Centre (WOUDC). In the most recent 5-year interval, the number of Brewer sites is almost equal to the number of Dobson sites.
Updated in 2013 from Fioletov et al., JGR, 2008
EC Brewer at NOAA at SPO vs. other instruments
WMO Antarctic Ozone Bulletin No 6/2013
Seasonal variation of the noontime UV Index at Eureka. The
top (first) panel compares noontime UVI measurements
performed in 2011 (red dots) with the average noontime UVI
(blue line), the range between the 10th and 90th percentile
(dark shading), and the range of historical minima and maxima
(light shading). The second panel shows the 2011 UVI
anomaly in absolute terms, calculated as the difference
between measurements and the average. The third panel
shows the relative UVI anomaly calculated as the percentage
departure from the climatological mean. The fourth panel
shows a similar anomaly analysis for total ozone derived from
satellite measurements. Vertical broken lines indicate the
times of the vernal equinox, summer solstice, and autumnal
equinox, respectively.
Form Bernhard et al., ACP, 2013
60% above the normal
Brewer applications: UV in the Arctic
Brewer UV from 3 Arctic Brewer sites (Resolute,
Eureka, Alert) are used in NOAA Arctic Report Card,
BAMS State of Climate report, and other publications
In the spring of 2011, they reported UV levels that are
60% higher than normal
Brewers application: UV Index forecast validation
Scatterplots and linear regression fits of EC and NOAA forecast methods (FM) plotted against collocated Brewer measurements. Blue open circles show EC forecasts, and red plus signs show NOAA forecasts. A small amount of random noise is added to the UV index data for better visualization. Four major weather types are represented: cloud-free sky (type 1), light clouds (type 2), heavy clouds (type 3), and rain (type 4). The correlation coefficients R between the measured and forecast values are also shown.
From He et al., JAMC, 2013
Brewers are used EC and
NOAA UV Index forecast
validation
The Brewer Triads and Calibrations
Toronto Brewers in March 2014
The triad update:
long-term record
Deviations of ozone values of
individual triad Brewers from the
mean of the three instruments. Each point on the graph represents a 3-month
average. Plots for ozone values from b-files
(top) and after re-processing (bottom) are
shown. The vertical line indicates the end of the
period used in the original triad paper.
Updated from Fioletov et al., GRL, 2005 (the triad paper)
Devia
tion
(%)
-8
-6
-4
-2
0
2
4
6
8
1985 1990 1995 2000 2005 2010 2015
Devia
tion
(%)
-8
-6
-4
-2
0
2
4
6
8
1985 1990 1995 2000 2005 2010 2015
Ozone from b-files
Reprocessed ozone with SL-corrections applied
Brewer 008
Brewer 014
Brewer 015
Brewers 008 and
014 were calibrated
in late 2008 σ = 0.5%
The main challenge in maintaining
the triad’s instruments is their
stability.
Calibrations and service every 2
years are necessary.
Toronto triad record vs. satellites Difference between triad data (available from the WOUDC) and various satellite instruments
-15
-10
-5
0
5
10
15
1978 1983 1988 1993 1998 2003 2008 2013
065 TORONTO, 44N, 79W, Brewer
Direct Sun Statistics 1978-1985 1986-1990 1991-1995 1996-2000 2001-2005 2006-2010 Mean Range
Number of days 368 1259 822 1217 1337 1437 1073.33 1069
Bias 0.16 0.05 -0.01 0.87 0.25 0.04 0.23 0.88
Daily sigma 2.33 2.4 2.4 2.16 2.03 1.73 2.17 0.67
Monthly sigma 1.13 1.03 1.05 0.9 0.75 0.69 0.92 0.44
Seasonal ampl. 0.56 0.15 0.33 0.24 0.32 0.32 0.32 0.41
Annual range 0.59 1.06 1.14 1.52 0.83 1.01 1.03 0.93
Seasonal mean differences between triad Brewer DS measurements and Nimbus 7 TOMS, Meteor 3 TOMS, EP TOMS, OMI, GOME, GOME-2, SCIAMACHY satellite total ozone data.
The whiskers represent 95% confidence limits for seasonal mean differences Table of the difference statistics. Note that the standard deviation of monthly mean differences is 0.7% in the most recent 5-year bin. updated from Fioletov et al., JGR, 2008.
Dif
fere
nce
in %
Pandora
Spectrometer
• Sun and sky spectrometer – measures solar spectra
• Can also work in ZS and MAX-DOAS modes
• Under development since 2006 (Jay Herman et al., NASA)
• Designed for satellite validation and pollution monitoring
• Operation and software design are similar to these for the
Brewer spectrophotometer (commands, schedules)
• Automated, established algorithms, data available in real
time
• Specifications:
– Czerny-Turner spectrometer with backthinned CCD detector
(Avantes)
– 270-530 nm at 0.6 nm spectral resolution, 4 pixels oversampling
– Wavelength independent FOV of 1.5 (FWHM)
– S/N of 400 at 400 nm
– T stabilized spectrometer ( enclose insulation under
improvement)
– High temporal resolution (<30 seconds per measurement)
– Simultaneous measurements of various trace gases incl. O3,
NO2, SO2, BrO, HCHO, water vapour
– Small size and portability (20 kg)
– Cost: ~$40k
• Two instruments were deployed in 2013 (McKay and
Toronto)
• Continue comparison with Triad instruments in Toronto.
The Pandora-Brewer difference
There is a 0% to 4% systematic difference between
Brewer and Pandora total ozone caused likely by the
difference in ozone absorption coefficients and their
temperature dependence.
Bre
wer
-Pan
dora
Diff
eren
cein
%
-2
-1
0
1
2
3
4
5
01OCT13 01NOV13 01DEC13 01JAN14 01FEB14 01MAR14 01APR14
5-day averages
Brewer 008 Brewer 014 Brewer 015 Brewer 145 Brewer 187 Brewer 191
The triad update - 2013
Tota
lO
zone
(DU
)
200
250
300
350
400
450
500
550
EST6:00:00 8:00:00 10:00:00 12:00:00 14:00:00 16:00:00 18:00:00
Brewer 008 Brewer 014 Brewer 015 Brewer 145Brewer 187 Brewer 191 Pandora 103 Pandora 104
An example: Feb 22, 2014
Diffe
rence
in%
-6
-5
-4
-3
-2
-1
0
1
2
Airmass value
1 2 3 4 5 6 7
Diffe
rence
in%
-4
-3
-2
-1
0
1
2
3
4
01OCT13 01NOV13 01DEC13 01JAN14 01FEB14 01MAR14 01APR14
5-day Statistics, mu<3
Brewer 008 Brewer 014 Brewer 015 Brewer 145 Brewer 187 Brewer 191
Brewers 014, 015, 191 returned from Mauna Loa
Old Triad
New Triad
Hg bulb was replaced in Brewer 008
Brewer and Pandora measurements at Toronto. Pandora measurements with 1.5 minute frequency were used to account for the difference in ozone due to difference in observation time between individual Brewer measurements.
Stray light causes an underestimation of ozone values by the single Brewer. Pandora measurements adjusted for the bias were used as a reference.
The whiskers represent 5st and 95st percentiles, the box
edges represent the 25th and 75th percentiles, the centre is
drawn at the median value
The old and new triads agree within 1%, but there are some systematic differences likely due to stray light. The long-term instrument stability is a challenge.
The biases between individual Brewer triad instruments and the “baseline.” The baseline was established using high-frequency Pandora measurements adjusted for the Pandora-Brewer bias:.The biases between Pandora and the new triad due to different ozone cross-sections were removed on a daily basis. The error bars represent 95% confidence limits for 5-day mean differences
New Triad Old Triad
Brewer UV measurements were normalized to modeled UV at 324 nm for sea level clear sky, no aerosol conditions. Noon values were
calculated as averages between 11:30 and 12:30. The whiskers represent 1st and 99st percentiles, the box edges represent the 25th and 75th
percentiles, the centre is drawn at the median value.
MLO Brewer observations: Based on cloud cover information, June and September are the best months for calibration, while March, April, and November are the worst ones
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Noon Values (11:30 - 12:30 LST)
Brewer 009 Brewer 119
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
7 8 9 10 11 12 13 14 15 16 17
Brewer 009 Brewer 119
Noon normalized UV at 324 nm values in different months Normalized UV at 324 nm values as a function of solar time
0
3
6
9
12
15
18
21
24
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Noon Values (11:30 - 12:30 LST)
Brewer 009 Brewer 119
Noon UV index values in different months
EC operates 2 Brewers at the NOAA Mauna Loa Observatory. Brewers 009 and 119 were installed in 1997. The most recent calibration of both instruments was in October 2013
Brewer 009 data for 1997-2012 and Brewer 119 data for 2003-2012 were used for this slide
Sun seen through fume
cloud Kilauea (photo by J.D. Griggs,
http://pubs.usgs.gov/of/2007/1114/)
MLO Brewer observations:
Volcanic SO2
The activity of Kilauea volcano near Mauna
Loa has increased after 2007
This may affect ozone calibration activities, particularly for Dobsons.
SO2 values as high as 50 DU under clear sky and as high as 400 DU
under cloudy conditions (with the multiple scattering effect) were seen.
Note that the Observatory (3400 m) is located above the volcano (1222
m) otherwise column SO2 would be even larger.
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 DU
OMI mean total column SO2 over Hawaii in 2005-2007 and 2008-2010 Mauna Loa UV spectra, April 26, 2008, 22:53 UTC (12:33 LST), Brewer #009, SO2=400 DU due to multiple scattering within the cloud.
290 300 310 320Wavelength (nm)
1.0E-6
1.0E-5
1.0E-4
1.0E-3
1.0E-2
1.0E-1
Irra
dia
nce (
W/m
2/n
m)
Statistical model estimation
3 std. deviations envelope
Measurement
290 295 300 305 310 315 320 325Wavelength (nm)
1
10
100
1000
10000
Ra
tio
(expe
cte
d/m
easure
d)
0
5
10
15
20
25
SO
2 a
bso
rption
(cm
-1 b
ase e
)
Global UV spectrum expected in absence of SO2
Measured spectrum
Ratio: expected/measured
MLO Brewer and Dobson observations Brewer ozone retrievals are not sensitive to SO2, while Dobson overestimates ozone in presence of SO2
Tota
lO
zone
(DU
)
220
230
240
250
260
270
280
16OCT13 01NOV13 16NOV13 01DEC13 16DEC13 01JAN14
Brewer 009 Brewer 014 Brewer 015 Brewer 017 Brewer 119 Brewer 191 Dobson
Large Dobson-Brewer differences
correspond to high SO2 values
The last
day of the
calibration
trip
The whiskers represent 10st and 90st percentiles, the box edges represent the 25th and 75th
percentiles, the centre is drawn at the median value. Dobson measurements (direct sun or blue
zenith) are taken once a day near local noon. Dobson data were provided by NOAA.
SO2=2 DU
SO2=8 DU
SO2=5 DU
Tota
lS
O2
(DU
)
-5
0
5
10
15
20
25
30
35
10:00:00 12:00:00 14:00:00 16:00:00 18:00:00
Brewer 009 Brewer 119
Total column SO2 measured by
Brewers 009 and 119 measured
on November 20, 2013.
Dobson and Brewer
ozone measurements
in October-December
2013.
Dobson measurement was at 13:00 HAST
New Brewer ZS algorithm: The same parameterization, but only 2 parameters instead of 9 are estimated from measurements Fioletov, V. E., C. A. McLinden, C. T. McElroy, and V. Savastiouk (2011), New method for deriving total ozone from Brewer zenith
sky observations, J. Geophys. Res., 116, D08301, doi:10.1029/2010JD015399.
The Brewer ZS algorithm does really not work when
μ>4 and ozone>300: the Brewer wavelengths and
weighting coefficients produce values that are not
sensitive to ozone.
The plot shows weighted sums of logarithms of zenith
irradiance intensities (G) as a function of total ozone for
various values of slant path (μ) for high latitudes. The
model calculations were done for albedo = 0.80. G shows
little sensitivity to total ozone when μ >4 and total
ozone is greater than 400.
The shape of the vertical ozone profile affect the ZS
retrievals when when μ>3.
Difference between DS ozone daily means and ZS ozone
means for different µ values for Churchill (59°N). ZS data were
processed using models based on midlatitudinal (black) and
high‐latitudinal (gray) ozone profiles. Calculations were done
using 0.8 albedo for December–April and 0.05 for the rest of
the year. The mean values (horizontal lines) with 2 standard
errors of the mean (vertical bars) are shown.
UV calibration: comparison between 40 and 50
cm calibration systems (4 identical UV lamps
and data logger on both systems)
The combined effect of polar ozone depletion and high tropopause is seen below for March 17, with
a large ozone anomaly (30-35% below normal) centered over the most populated areas of Europe.
Work with Kipp and Zonen to facilitate service
and maintenance and improve instrument
reliability • Replace NFS80 with NFS110 power supply -more current on 24V line for more reliable micrometer motor
movement
• Higher power level applied to standard lamp - improves stability of dead time and run stop test results
• Ball-end grating arm and micrometer points-eliminates potential source of hysteresis in micrometer movement
• Rotary connector installed in trackers along with heater system - cables do not rotate with tracker during day, eliminates data and power cable movement stress and breakage, internal shut off switch not required, no accidental breakage of shut-off string due to accidental over-rotation during drive plate cleaning, tracker heater helps to ensure better tracker movement in cold environments
• Use 296.728 nm hg single peak line for hg test instead of 302.1nm doublet peak line - reduce hg lamp warm-up to 2 minutes from 5 and reduce micrometer positioning changes since doublet line peak can change with lamp age, reduces hg lamp aging, saves time for more ds, uv, etc.
• Neutral density filters with tighter tolerances on specified attenuation values-prevents artificial spikes in ozone measurements when successive neutral density filters are introduced into the optical path
• Magnetic window in back tracker cover with chain link to tracker cover bolt - facilitates visual inspection and tool-free cleaning of the drive plate edge, eliminates tracker seal issues due to cover bolt spacer positioning errors
• 1/8” Hole in center of blocked filter - to determine and confirm the UV focusing of the Brewer
• Micrometer movement referenced to spectrometer LEDs - allows for reproducible micrometer reset even after reinstallation/replacement of the micrometer and/or pushrod replacement
• Power and data cables rated to -70 C - More reliable in colder environments
Brewer operational issues that still need to be
addressed
• Long-term stability for micrometer motor movement—mostly resolved by new NFS110 power supply but still have instances of poor micrometer movement and jamming
• Standard lamp power—needs to be adjustable as it was in single board Brewers so that standard lamp intensity can be optimized for each lamp as required in order for stable and acceptable diagnostic test results
• Sensitivity to power issues—single board Brewers appear to be sensitive to power failures or brownouts and sometimes require config and/or firmware to be re-installed
• PMT sensitivity decline over time-- Brewer PMT’s have been originally set with a relatively low high voltage setting and the NFS80 power supply may not have been providing the necessary current at 24V
• PMT acceptance testing prior to installation into Brewers--one of our PMTs recovers slowly after being exposed to light and residual signal can bleed over into the next measurement
• Noisy negative voltages—understand the cause of the variability to confirm no effect on the instrument
Strategy
• Maintain smaller network but with assured stream of high
quality data with 2+ Brewers at each site plus other
instruments
• Let the Brewer do what it can do best, i.e., to produce
high quality and stable over time total ozone and UV data
and use other instruments for other tasks
• Focus on implementing what has been developed by
other, rather than developing everything ourselves
• Strongly support unification and standardization of
measurements and data processing
• Open to suggestions