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Beltsville 0.68
Padonia 0.3
Fairhill 0.95
Aldino 0.7
Edgewood 0.77
Essex 0.79
HCHO Fairhill
Beltsville 1
Padonia 0.86
Fairhill 0.82
Aldino 0.51
Edgewood 0.42
Essex 0.48
HCHO Beltsville
Beltsville −0.42
Padonia −0.69
Fairhill 1
Aldino 0.75
Edgewood 0.82
Essex 0.85
HCHO Chesapeake Bay
How far away from the retrieved site can this layer average be used?The drop of HCHO spatial correlation is less significant than NO2; proximity tends to increase the correlation, but features like the Chesapeake-to-Fairhill correlation are
unexplained.
Blue-red scale runs from –1 to 1
Beltsville 0.68
Padonia 0.77
Fairhill 0.14
Aldino 0.71
Edgewood 0.22
Essex 0.62
NO2 Padonia
Beltsville 0.23
Padonia −0.15
Fairhill −0.06
Aldino −0.01
Edgewood −0.42
Essex 0.39
NO2 Chesapeake Bay
Beltsville 0
Padonia 0.26
Fairhill 0.86
Aldino 0.32
Edgewood −0.12
Essex −0.03
NO2 Fairhill
Beltsville 0.95
Padonia 0.19
Fairhill −0.12
Aldino 0.41
Edgewood 0.24
Essex 0.59
NO2 Beltsville
How far away from the retrieved site can this layer average be used?NO correlation drops rapidly with distance, although better correlations result if 0–1.2 km averages
may be used. The latter layer appears to be most significant for daily smog ozone production and loss, although ozone itself is correlated up to deeper layers, e.g. 3 km.
Notice: Chesapeake Bay samples show more isolation of lowest levels and lower correlation.
Blue-red scale runs from –1 to 1
Relevant horizontal resolution for O3 can be rather coarse in many (!) instances. Relevant horizontal resolution for NO2 and HCHO is finer.
2
3.
2
0.2-1.2 km average NO2
NO2
Color-codes are shown left on spirals map
Previous Motivating Results:Chatfield and EssweinAtmos. Environ, 2012, shows that 0-3 km layer-average ozone often provides excellent estimates of near-surface “relevant” O3 in a 0.1-0.5 layer. Correlation coefficients, r, shown below, range from ca. 0.79 to 0.94. Low r values occur in regions of known strong layering. Data came from O3-sondes launched by NASA (A. Thompson et al. ),
NOAA (S.Oltmans et al.), and Environment Canada (D. Tarasick et al.). However, many stations were rural and the variability of retrieval skill/relevance in a complex urbanized setting could not be explored.
3
2
1
0.2
0.5
0.2
0.50.5
z, km
What can be sensedremotely
What is relevantto air pollutionconcerns
Differentialadvectionmay changeair composition
Daytime convec-tive eddies
Nocturnal shear-driven eddies
Subsidence and calm may allow minimal change in air composition
timeNoon Noon NoonMN MN MN MN
Residual layer top
Mixed layer top
Relative calm and subsidence conditions
0 1 2 3 4 5
1000
800
600
400
200
Sensitivity: cumulative DoFS from surface
Pre
ssur
e, h
Pa
Ultraviolet+Infrared/Ultraviolet+Visbile/
UV,/Vis,/and/IR/°/°/°/
Infrared/
39.8
2011Ͳ07Ͳ02�RF02�Loop�2
39.6
Fairhill
39.4
Padonia
Aldino
39.2
Beltsville Edgewood
Essex
39.0
38.8
-77.0 -76.8 -76.6 -76.4 -76.2 -76.0 -75.8 -75.60 6 8 6 6 6 6 6 0 5 8 5 6
Washington*DC!
*Downwind*Suburb!
*Doubled**(Internal)*BL:*due*to*Bay*Breeze!
*Rural:*out*of*plumes!
Quick*characterizaDon*of*sites*relaDve*to*metropolitan*area.*ColorGcodes*are*used*below*to*idenDfy*local*influences*on*HCHO*and*NO2.**
Time%sequence+of+ver0cal+climbs+and+descents+…+all+day.+Color%coded.++
6:30+AM:+Scien0sts+going+on%board+P%3B+aircraD+for+the+day’s+measurements++take+dramamine+against+air%sickness.++
DISCOVER-AQ: Deriving Information on Surface Conditions from COlumn and VErtically Resolved Observations Relevant to Air Quality, Hundreds of aircraft profiles around an urbanized region area • reveal smog in detail and provide a testbed for retrieabality studies and relevance. Near-surface pollution is one of the most challenging problems for Earth
observations from space…
Investigation Rationale
Near-surface information must be inferred from column-integrated quantities obtained by passive remote sensing from downward-looking satellite instruments.
Some constituents have large relative concentrations in the stratosphere and/or free troposphere (e.g., O3 and NO2) making it difficult to distinguish the near-surface contribution to the total column.
22
Height of the box matters
It matters about how well the pollution is mixed
From space, the size of the measurement pixel matters
If we knew these well, ground concentrations would relate well to space measurements
The DISCOVER-AQ airborne study repeatedly made spirals over various urban,
industrial, transportation, and rural sites in detail around the Baltimore-Washington area
in July, 2011. We compare mixing ratios appropriately averaged for thin layers at the
bottom of the spirals, 0.2-0.5 km, the relevant, with those over a deeper layer, “the
retrievable,” which, for O3, was over a 0.2-3.0 altitude. For NO2 and HCHO, the region
0.2 – 1.2 km was found during the study to be more appropriate, based on observed
patterns rather than retrievability studies — these species were limited to lower
altidtudes.!
O3 (ppb) (Weinheimer) layer meanTime range: 4.0 to 18.0 hrs EST
Time bin (for each flight): 120 minutes
20 40 60 80 1000.0 to 3.0 km
20
40
60
80
100
0.2
to 0
.5 k
m
Corr 0.93
1 2 5 10
11 14 16
20 21 22
26 27 28 29
Ozone profiles DISCOVER-AQ 1-29 July 2011 0-3 km 20-120 ppbv Daily obs in yellow All profiles in gray
0 km
20 ppb 75 ppb 120 ppb
1 km
2 km
3 km1 2 5 10
11 14 16
20 21 22
26 27 28 29
Ozone profiles DISCOVER-AQ 1-29 July 2011 0-3 km 20-120 ppbv Daily obs in yellow All profiles in gray
0 km
20 ppb 75 ppb 120 ppb
1 km
2 km
3 km
0 2 4 6 8 10
02
46
810
0-3 km average HCHO
0.2-
0.5
km a
vera
ge H
CH
O overall: r = 0.79
HCHO deep-layer to near sfc conversions vary consistently by location
BeltsvillePadoniaFairhillAldinoEdgewoodEssexHighwayChesapeake BayUMBC
0 5 10 15 20 25
05
1015
2025
0-3 km average NO2
0.2-
1.2
km a
vera
ge N
O2 overall: r = 0.97
Good representation of PBL except near sources, with Bay Breeze
BeltsvillePadoniaFairhillAldinoEdgewoodEssexHighwayChesapeake BayUMBC
0 5 10 15 20 25
05
1015
2025
0-3 km average NO2
0.2-
0.5
km a
vera
ge N
O2 overall: r = 0.85
scattered NO2 deep-layer to 0.2-0.5 km relations despite good representation of PBL
BeltsvillePadoniaFairhillAldinoEdgewoodEssexHighwayChesapeake BayUMBC
Beltsville 0.68
Padonia 0.77
Fairhill 0.14
Aldino 0.71
Edgewood 0.22
Essex 0.62
NO2 Padonia
Beltsville 0.23
Padonia −0.15
Fairhill −0.06
Aldino −0.01
Edgewood −0.42
Essex 0.39
NO2 Chesapeake Bay
Beltsville 0
Padonia 0.26
Fairhill 0.86
Aldino 0.32
Edgewood −0.12
Essex −0.03
NO2 Fairhill
Beltsville 0.95
Padonia 0.19
Fairhill −0.12
Aldino 0.41
Edgewood 0.24
Essex 0.59
NO2 Beltsville
How far away from the retrieved site can this layer average be used? NO2 correlation drops rapidly with distance, although better correlations result if 0–1.2 km averages
may be used. The latter layer appears to be most significant for daily smog ozone production and loss,
although ozone itself is correlated up to deeper layers, e.g. 3 km.!
Notice: Chesapeake Bay samples show more
isolation of lowest levels and lower correlation.
Blue-red scale runs from –1 to 1
Beltsville 0.68
Padonia 0.3
Fairhill 0.95
Aldino 0.7
Edgewood 0.77
Essex 0.79
HCHO Fairhill
Beltsville 1
Padonia 0.86
Fairhill 0.82
Aldino 0.51
Edgewood 0.42
Essex 0.48
HCHO Beltsville
Beltsville −0.42
Padonia −0.69
Fairhill 1
Aldino 0.75
Edgewood 0.82
Essex 0.85
HCHO Chesapeake Bay
How far away from the retrieved site can this layer average be used? The drop of HCHO spatial correlation is less significant than NO2; proximity tends to increase the correlation, but features like the Chesapeake-to-Fairhill correlation are unexplained.!
Blue-red scale runs from –1 to 1
NO2!
4ºx8º%
DISCOVER-AQ AIRBORNE MEASUREMENTS QUANTIFY HOW SATELLITE-RETRIEVABLE BECOMES HEALTH-RELEVANT
SMOG OZONE AND ITS FORMATION
HCHO !
Beltsville 0.33
Padonia 0.61
Fairhill 0.55
Aldino 0.47
Edgewood 0.41
Essex 0.54
O3 Chesapeake Bay
Beltsville 0.88
Padonia 0.83
Fairhill 0.87
Aldino 0.92
Edgewood 0.96
Essex 0.91
O3 Edgewood
Beltsville 0.84
Padonia 0.8
Fairhill 0.93
Aldino 0.89
Edgewood 0.83
Essex 0.75
O3 Fairhill
Blue%red(scale(runs(from(0(to(1.!
ude
(ft) 8000
10000
BeltsvillePadoniaFairhillAldinoEd d
DISCOVER-AQ 10July 2011
Pre
ssur
e A
ltitu
2000
4000
6000 EdgewoodEssex
CO2 (ppmv)370 380 390 400 410
0
2000
5
6 7
1 1 2
4
5 12 5
Red numeral shows the number of ground stations with excedances: July had the most: 12 of 15 stations
Symbol connects flight day with scatterplot values for O3 shown below left
Excedance days: thanks to J. Hains, MD Dept. of Environ.
The Challenge: remote sensing gives lower tropospheric information, but air pollution concerns emphasize near-surface concentrations. These can differ.
Is the “retrievable” (possible) actually relevant to air pollution/health concerns?
We find:Unusually informative maps showing health-relevant surface smog
pollution may be expected from developing multi-wavelength retrievals from space, e.g., in upcoming missions being planned by the United States “TEMPO” (launch 2018, and “GEO-CAPE”, implemented 2021) and by European and Asian agencies.
The key is that ozone and its precursors are vertically correlated in layers deep enough that to allow be, at least when appropriate situation-to-situation correlations are computed.
Also: concentrations in the lower troposphere tend to mirror 0.2 – 1 km concentrations. This may be due to lofting and dilution of fresh influences.
Use of simple meteorological understandings and site-knowledge improve the accuracy of the correlation analysis.
We also assert: Concentrations of O3 and NO2 at surface monitors may be
so influenced by local sources (e.g., a congested traffic intersection) that they are less relevant to ozone production and general ozone levels of a region than PBL averages.
Even with the development of sophisticated new algorithms combining UV and Visible wavelengths, TEMPO aspires to a precision of ±10 ppb in the region 0–2 km (K. Chance personal communication), and with fully resolved (integrated DoFS from surface up) layers closer to 3 km deep, as shown in Chafield and Esswein (Atmos. Environ., 2012) and Natraj et al. (Atmos. Environ., 2011). These estimates are useful for North American situations near sea level, excluding the Intermountain West and Front Range.
These are the encouraging results from the “DISCOVER- AQ” studies of July, 2012. They reinforce the conclusions of Chatfield and Esswein, 2012.
Relevant:We chose as relevant a region 200–500 m based on (a) the practical fact that this was the lowest region in which the DISCOVER-AQ made measurements (see the typical flight altitude graph) and (b) the that these pollutants decay significantly altitude above ~1.2 or 1.5 km. (c) The choice of the lower 200–500 m layer focuses on concentrations that • describe well a well-mixed region during high-PBL-top afternoon periods • describe the near-surface concentrations during lower-PBL-top periods• describe a region with sufficient mass to be relevant to transport-and-chemistry evaluations of PBL concentrations.
TEMPO is an exciting developmental stage that opens opportunites for theGEO-CAPE mission, Proposed NASA Geostationary satellite: C A P E : Coastal and Air Pollution EventsAir Pollution Instruments: UV-Vis Spectrometer: O3, NO2, HCHO, SO2, Aerosol
(PM2.5) Solar-IR: CO, CH4. Thermal IR: O3, NH3, …
Shown in the figure are estimates of resolution of successive independent layers starting at sea level. TEMPO will have capabilities that exceed those shown in the orange (Ultraviolet+Visible) line above. It exploits the uniquely large sensitivity of the visible due to Rayleigh scattering in regions very near sea level (note rapid increase of orange line). Are these layers informative for nose-level ozone?
In our comparisons, we will integrate the ozone in the aircraft soundings to give estimates of what the satellite can resolve (the retrievable layer, shown in yellow) and the layer or air pollution relevance (the relevant layer. shown in green). We then examine the correlations of these layer's averaged ozone amounts and find them useful and reasonable in light of simple meteorology.
(3) Now correlate the deep-column averaged mixing ratio (retrievable) at one station (the circled one) to the shallow (relavant) correlation at all stations, including distant ones. Notice the large horizontal correlation scales of O3 (despite the many variations
seen in the profiles above). Note also the rapid fall-off of correlation for NO2. HCHO
shows similar but less dramatic fall-off of correlation, and also shows some weather response like O3.
Denver&...
most&of&conven.onally&polluted&USA
deeperlayer • P(O3)~ f ( jHCHO->rads x HCHO , NO ) !
• HCHO and jHCHO->rads are !measurable !
(j is ~ UV reflected radiation) "• NO derivable from NO2, O3, "• if O3 is known!"
Can we measure smog ozone production from space?
![NO] =
jNO2 / ( kN[O3] + kH[HO2] )
Most likely, satellite instruments provide checksums on models, showing that vertical integrals of key precursors are understood, … or not"
A caricature: how complex it can be "
How simple it can be "
small correction"
(1) Main variations in ozone correlations are due to weather, day to dayl Days alternate in mixing deeply and responding to subsidence. Match symbols on scatterplot and "swarm" profiles above to confirm the effects of weather.
(2) Main variations in NOx and HCHO correlations are due to geographical location, with regions experiencing Bay breezes and similar air-mass transitions showing lower, ... or different, correlations. This agrees with the findings in Chatfield and Esswein (2012) regarding a similar analysis of cities near the Great Lakes or the Western coastline, also with low correlation.
How far away from the retrieved site can this layer average be used? Maps below show the correlation coefficient between 0–3 km “retrievable” average at the circled location and the 0.2–0.5 km average at other spiral locations. While correlations over land are high, diminishing with distance, correlations with the 0.2–0.5 km average for samples over the Chesapeake Bay are small.
Conclusions:&
> Satellite retrieval methods are useful in determining ozone and ozone-producing chemicals for regions determining general surface-level conditions, even if they do not resolve very local variations due to surface-layer emissions. > Extended observations: Geostationary satellite sensing allows even better inference based on analysis of, e.g., time-of-day (mixed-layer growth) variations if the meteorology of mixing can be brought in. Characterizations of the lower 1–2 km are typical of the whole budget of a day’s pollutant loading, including significant material in the “residual layer” above early morning mixing tops. This large mass of pollutant is essentially unmeasured by surface monitors.
> Satellite missions such as the upcoming TEMPO EV-I mission and the proposed US mission GEO-CAPE can provide considerably more information useful for environmental analysis and indicate the most economic modes of amelioration of smog air pollution.> Correlations of layer-averages of O3 and HCHO in the horizontal provide significant information beyond the "footprint" sampling area of a satellite (up to 20 km for O3) in many situations, although land-water boundaries can interrupt this correlation. Results are consistent with the ozonesond studies, mostly non-urban, reported by Chatfield and Esswein (Atmospheric Environment, 2012)> However, the more reactive species nitrogen dioxide and formaldehyde tend always to require much more detailed geographical sampling.
> Useful quantitative estimates of the layer-mean ozone chemical production rate P0(O3) also appear possible, since organic reactivity and NO concentrations may be inferred from products measurable by remote sensing.
> Large areas of the United States suffering from ozone above 70–75 ppb, the high-altitude West, are not sampled well according to theory developed so far. They lack sufficient Rayleigh scattering for effective visible-band response due to their altitude.
> TEMPO should provide remarkable pollution data relevant to health, but the EV-I mission inherently cannot rise to answer the questions that they raise. Fortunately, these answers can now be more economically answered with modest added research and then added remote-sensing instrumentation.
Colored profiles show growth of PBL and pollution during one day.
Robert F. Esswein1,2, Robert B Chatfield2, James H Crawford3,
Andrew Weinheimer4, Alan Fried5, John D W Barrick3
1. Bay Area Environmental Reasearch Institute, Moffett Field , CA, United States.
2. Atmospheric Science, NASA (Ames), Moffett Field, CA, United States.3. NASA (Langley), Hampton, VA, VA, United States.4. National Center for Atmospheric Research, Boulder, CO, United States.
5. Arctic and Alpine Research, University of Colorado, Boulder, CO, United States.
This comparison shows that theaverage of detailed pollutant concentrations in the equations to the left is very close to the calculations made with column averages, for 3-km averages. Hence satellite retrievals may be used to estimate ozone chemical production.
Ozone chemical production rate calculated using organic reactivity and NO concentrations following Chatfield et al, Atmos. Environ. 2010, and 2013 (submitted this month).
P3-B spirals (helices) shown right and sample ozone profiles left.
