THE OPTICAL PROPERTIES OF ATMOSPHERE DURING NATURAL FIRE EXPERIMENT IN CENTRAL RUSSIA AND THEIR IMPACT ON UV IRRADIANCE Nataly Ye. Chubarova Moscow State University, Geographical Department, Meteorological Observatory, Alexei N. Rublev IMP, KURCHATOV Center, Moscow,Russia Allen R. Riebau USDA Forest Service Wildlife, Fisheries, Watershed and Air Research Washington, DC

Meteorological parameters in summer-fall 2002 and climatic values ( ):

Clear sky conditions Average Aerosol Optical Thickness for : AOT_500=1.6 MOSCOW Moscow river MO MSU

Average AOT_500=1.7  2

CLEAR SKY FIRE SMOKE ( ) TAGANSKAYA SQUARE, MOSCOW

CLEAR SKY FIRE SMOKE, (COURTESY OF ROBERT MUSSELMAN) RED SQUARE, MOSCOW

AEROSOL OPTICAL THICKNESS IN MOSCOW AND MOSCOW SUBURBS (Zvenigorod) FROM CIMEL AND HAND HELD HASEMETERS. MAY- SEPTEMBER 02.

Monthly mean aerosol optical thickness from Cimel in 2002 (in blue) and AOT retrieved from actinometer following the method Yarkho& Tarasova [1991]

Single scattering albedo (SSA) in conditions with forest fires and in typical optical conditions. Moscow,

Surface ozone concentration (active ozone monitor 2B Technologies, Inc) and aerosol optical thickness (CIMEL) changes in summer 2002

Gas concentration in low troposphere in summer 2002 and absorption coefficients for different gases Maximum allowable concentration (Russian standard) for NO2: 80 mg/m3 O3: 160 mg/m3 SO2: HCHO:

Concentration of several atmospheric gases in summer 2002.

Spectral dependence of optical thickness for the average concentrations of different gas species. Summer 2002.

Solar angle dependence of solar fluxes in different spectral ranges. Clear sky conditions, UV380Q_eryth SI PAR

Loss of solar irradiance in different spectral ranges. Clear sky conditions normalized at h o =30 degrees and X=300DU.

MODEL INPUT PARAMETERS: 1. Aerosol characteristics from Cimel sun photometer: AOT at nm, SSA at 441nm, asymmetry factor at 441nm. 2. NO2, SO2, O3, HCHO gaz concentration for the low 0-1 km layer from ground measurements. For surface ozone we take daily maximum concentration. TOMS data for total O3. 3.VERTICAL PROFILES: In Troposphere: HCHO - 0.2ppb, NO2 - 1ppb (aircraft measurements), SO ppb. In Stratosphere: -WCP 112, Ozone distribution: Subarctic summer model

Effect of different gases on attenuation of Q erythema (dQe = Qe_gaz/ Qe_clear_from_all_gases,%) observed in 2002 in clear sky conditions. Model simulations.

Relative difference between Q erythema calculations with gaseous absorption (red circles) and without it (black circles) and Qer measurements as a function of AOT. h o >25 degrees. The remaining dependence on AOT may be the indicator of 1. Less value of SSA? 2. Problems with non account of forward scattering at large AOT? 3. Larger gas concentration in upper troposphere or existence of other gas ?

Relative difference between Q less 380nm calculations with gaseous absorption (red circles) and without it (black circles) and Q less 380nm measurements as a function of AOT. h o >25 degrees.  10% of difference is in accordance with the difference in calibration factor CF utilized and CF obtained in Greece in 1999, which was not applied to these data. NOTE THAT: Brewer UV spectral measurements are lower than TOMS estimations [Fioletov et al., 2002]. Also there were different biases between TOMS and New Zealand (zero!) and European spectral measurements [MkKenzie et al., 2000]

Effect of diffuse irradiance to aerosol optical thickness underestimation Close AOT values for NIP and A-50 and their difference from CIMEL sunphotometer MEAN the presence of coarse aerosol particles responsible for scattering in the instrument FOV.

Single scattering account in the instrument FOV:

Aerosol size distribution according to Dubovik&King retrieval method [2000] during clear conditions (blue lines) and fires (red lines).

The effect that may present due to forward scattering into the FOV. Aerosol size distribution in aerosol continental model (WCP-112, 1986): Dust aerosol size distribution model as a part of continental model and when is cutted off at 15  m: This particle size, if exists in nature, may be responsible for large forward peak  r 4.

Illustration: The calculated difference between exact AOT and AOT’ measured in CIMEL FOV for continental type of aerosol at different airmass m.

Comparison with TOMS retrievals of erythemally weighted irradiance  15% of TOMS overestimation for August and September.

CONCLUSIONS: 1. The most severe natural fire event over Central Russia. AOT is more than times larger than the monthly mean aerosol optical thickness in summer-fall 2002, reaching AOT_500>3. 2. Flux validation approved that smoke aerosol has very slight absorption ( SSA  0.95 from CIMEL retrievals). 3. In UV spectrum we should take into account the effects of gaseous absorption (mainly by NO2) both in clear sky and fire conditions. But sometimes other gases (O3, SO2) also play significant role. 4. NO2 may be responsible for the difference in comparisons of ground UV measurements with TOMS estimates especially in the polluted regions. 5. It may be the effect of forward scattering into the CIMEL FOV due to the existence of large aerosol particles that is especially significant at high solar zenith angles. If they really present in nature? Need further studies..

Acknowledgements: We would like to thank: 1. AERONET team (Brent Holben, Alexander Smirnov, Oleg Dubovik, Ilya Slutsker, David Giles, etc.) for help in maintaining of measurements and providing a lot of consultations. 2. Moscow Ecological Monitoring Office for providing the data on concentration of some gas species and «PLANETA» Scientific Center for providing satellite images of fires around Moscow. 3. Dr. Wei Min Hao from USDA Forest Service for providing the Hasemeters for aerosol studies at Moscow suburbs. 4. NOAA for producing the backward trajectories over Moscow. 5. The staff of Meteorological observatory of MSU and, personally, V. Rozental’, N. Uliumdzhieva, A. Yurova, Ye. Stolyarova for technical help with instruments maintanence. This work was done partially under the support of the USDA Forest Service in the frame of the project ‘‘Solar Radiation and Weather Variability Influences on Russian Sub-Boreal Forest Phenology.’’