OBSERVATIONS OF NITRATE RADICAL

)NO3IN THE ISRAELI ( TROPOSPHERE

Daniel Pedersen Eran Tas Valeri Matveev Mordechai Peleg Menachem Luria

The Institute for Earth Sciences Hebrew University of Jerusalem Acknowledgements

• Support: Ulrich Platt and Jutta Zingler, University of Heidelberg • Indirect Funding: Ministry of Environment – Middle East Regional Cooperation Program, USAID • Student Workers – Yair Morag, Erez Sariel, Roi Tzidon – Ran Avni – David Asaf • Kibbutzim Neot Smadar, Yizrael, Netiv Halamed-Hei, • Nehusha

Institute of Earth Sciences, Hebrew University Outline

• Atmospheric Chemistry – Daytime & nighttime

–NO3 radical important at night • Methods – Measurements, Instruments – Spectral Analysis

• NO3 Measurements 2003 - 2005 – winter, summer, spring – background, rural • New Project – long Term URBAN (TURBAN) measurements

Institute of Earth Sciences, Hebrew University Atmospheric Chemistry of

Nitrate Radical (NO3) Atmospheric Free Radicals

• Compounds such as OH, HO2, ROx, NO3. – high reactivity; low concentrations (e.g. 10-13 for OH) • OH radical created by sunlight 1 O3 + hν Æ O( D) + O2 1 O( D) + H2O Æ 2OH

OH +VOC Æ… Æ CO2 +H2O

• usually the major cause of VOC scavenging, conversion of NOX to NOY, and ozone formation during daytime

Institute of Earth Sciences, Hebrew University Nighttime Chemistry

• In absence of sunlight, OH no longer generated directly.

• The important formation pathway for NO3

NO2 + O3 → NO3 + O2

• NO3 photolyzed effectively during daylight, and only accumulates in the dark – oxidizing agent for VOC

– sink for NOX; conversion to NOY – production of RO2 radicals, aerosols

NO3 + NO2 + M <→ N2O5 + M

N2O5 + H2O → 2HNO3

Institute of Earth Sciences, Hebrew University NO3 Tropospheric Chemistry

JGR, 2001

Institute of Earth Sciences, Hebrew University Detection of NO3 Radicals

• NO3 absorption measured – stratosphere (Noxon et al. [1978]) – troposphere (Platt et al. [1980], Noxon et al. [1980])

• Only a few long term measurements of NO3 – Marine Boundary Layer (e.g. Heintz,1996) – up to ~20 ppt – Continental Boundary Layer (Geyer, 2001; Platt,2002) Rural, semi-polluted site near Berlin; nearby forest – up to ~85 ppt

Institute of Earth Sciences, Hebrew University Measurement Methods

A number of different analytical techniques have been used in the laboratory and field to measure Radical species

• Differential Optical Absorption Spectroscopy (DOAS) • Laser Induced Fluorescence (LIF) • Matrix Isolation Electron Spin Resonance (MI-ESR) • Chemical Ionisation Mass Spectrometry (CIMS) • Peroxy Radical Chemical Amplification (PERCA) • Cavity Ring-Down Spectroscopy (CARDS)

Institute of Earth Sciences, Hebrew University The InstituteField for EarthMeasurements Sciences Hebrew University of Jerusalem Goals & Objectives

• Document NO3 levels in & Mediterranean environment (Israel)

• Estimate the importance of NO3 radical in scavenging organic compounds and as a sink for NOX (nitrogen oxides)

Institute of Earth Sciences, Hebrew University DOAS: Differential Optical Absorbance Spectrometer • Pioneered by Platt, et al. [1979] • Optical absorbance, 6 – 10 km path length NO2 • Xe lamp in a transmit/receive telescope NO3 • spectrometer: 1024 channels, 60nm window O3 • Spectra fit to standards; very labor intensive SO -9 -12 2 • order of sub-ppb to ppt detection limits (10 -10 ) BrO • important method to measure NO , NO XO directly 2 3 IO … spectrometer mirror

Xe lamp reflectors

Reflectors Beer - Lambert Law

1  I (λ )  c = ln  0  σ (λ ) ⋅ L  I (λ ) 

– c the concentration of radicals (molecule cm-3) – σ(λ) the absorption cross section of corresponding radicals at wavelength λ – L the length of the light path – I(λ) the light intensities with absorption by radicals

– I0(λ) the light intensities without absorption by radicals

Institute of Earth Sciences, Hebrew University Differential Optical Absorbance

In the atmosphere, we cannot determine I0(λ) due to unknown extinction by broadband Rayleigh and Mie scattering. The basic idea of DOAS is to split the trace gas absorption cross section into two parts:

σ0(λ) that varies slowly with wavelength σ´(λ) that varies quickly with wavelength

I(λ, L) = I 0 (λ) ⋅exp[−(σ 0 (λ) ⋅ c ⋅ L + σ«(λ) ⋅ c ⋅ L)]

= I 0«(λ) ⋅exp[ − (σ«(λ) ⋅ c ⋅ L)] where

I 0«(λ) = I 0 (λ) ⋅exp[−(σ 0 (λ) ⋅ c ⋅ L)]

Introducing the differential optical density D´(λ) = ln((I0´(λ)/I(λ)), concentration can be written as: D«(λ) c = σ«(λ) ⋅ L

Institute of Earth Sciences, Hebrew University Differential Optical Absorbance

DOAS analyzes only the narrow absorption structures. This separation of the cross section can be performed by numerical filters [Platt, 1994], eliminating the broadband structures. Both reference and measurement spectra are treated with the same filters. Spectral matching procedures are used to fit the reference spectra to the measured spectra

The concentrations of the absorbing trace gases then are derived by correcting for background and lamp spectra • fitting and removing reference spectra of interfering species • fitting reference spectra of species of interest to remaining • spectra

Institute of Earth Sciences, Hebrew University Institute of Earth Sciences, Hebrew University

Nitrate Radical Concentrations Field Sites

• Neot Smadar • January 2003; July 2004; March-April 2005 • Background • Kibbutz Yizrael • June 2003 • rural, south of Afula • Kibbutz Netiv HaLamed-Hei • August-September 2003 • rural, major roadway • Moshav Nehusha • May-June 2004 • rural, remote • Kibbutz Ein Gedi • May-June 2004 • rural, remote

Institute of Earth Sciences, Hebrew University Neot Smadar, Winter 2003 Neot Smadar, Winter 2003 Neot Smadar, Winter 2003 Yizrael, Summer 2003 Yizrael, Summer 2003 Ein Gedi, Summer 2004 Ein Gedi, Summer 2004

Nehusha, Summer 2004 Nehusha, Summer 2004 Nehusha, Summer 2004

Nehusha, Summer 2004 Nehusha, Summer 2004

Institute of Earth Sciences, Hebrew University Nehusha, Summer 2004

After Geyer & Platt, JGR 2002

Institute of Earth Sciences, Hebrew University Neot Smadar, Spring 2005 Neot Smadar, Spring 2005 Neot Smadar, Spring 2005 Neot Smadar, Spring 2005 Neot Smadar, Spring 2005 Conclusions

• NO3 successfully measured at various seasons and locations • max levels exceeding 300 ppt • detectable concentrations limited to nighttime, peaking at 22:00 – 02:00 • sensitive to high relative humidity • related to emissions in Israel, less so for LRT

• Initial calculations for production and loss of NO3 accomplished

• Plans to model NO3 chemistry using detailed chemical mechanisms

Institute of Earth Sciences, Hebrew University TURBAN Project

• long Term URBAN measurements

of NO3 in Jerusalem

• Continuous monitoring of NO2 and NO3 by DOAS along 3.5 km light path • Older version of DOAS instrument with separate lamp located in Gilo neighborhood of Jerusalem

• Parallel monitoring of O3 at Hebrew University campus by analyzer co-located with receiving telescope • 2 years of measurements beginning summer 2005

Institute of Earth Sciences, Hebrew University TURBAN Project - Objectives

• First long term continuous monitoring of NO3 in an urban setting located in a semi arid region

• First such measurements of true NO2 in the Eastern Mediterranean

• Quantify NO3 concentrations, production, and oxidation potential

• Compare spatial distribution (different light paths) of NO3 and NO2 during joint measurement campaigns

• model NO3 chemistry using detailed chemical mechanisms

• Collaboration between Hebrew University and University of Heidelberg (Luria and Platt, PIs). • Supported by the German Israel Fund (GIF)

Institute of Earth Sciences, Hebrew University OBSERVATIONS OF NITRATE RADICAL

)NO3IN THE ISRAELI ( TROPOSPHERE

Daniel Pedersen Eran Tas Valeri Matveev Mordechai Peleg Menachem Luria

The Institute for Earth Sciences Hebrew University of Jerusalem