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Joint research activity 1:

Operational retrieval of vertical profiles of aerosol parameters from DOAS technique

Objectives and expected impact

Development of a novel method for the determination of the aerosol optical density and its vertical distribution using scattered sunlight. The method is based on the Differential Optical Absorption Spectroscopy (DOAS), which has been applied for three decades to measure a wide variety of gaseous species relevant to atmospheric chemistry. The advantages of the MAX-DOAS principle can be extended to the measurement of aerosol.

The most important impact from JRA1 is a new MAX-DOAS method consisting of a cost-effective, very simple and mobile instrumentation that can, in the future, be implemented at monitoring stations within EMEP. This activity also contributes to highly skilled employment in Europe.

Description of work

UHEI will develop, demonstrate and validate a fully automated MAX-DOAS instrument for measurements applying the described algorithm to derived aerosol properties. A network of three continuously operating MAX-DOAS devices will be installed. In addition, two instruments will operate on a campaign basis. The required hardware is simple, encompassing essentially a miniature spectrometer, a small telescope, a pointing mechanism, and a Personal Computer each. The aerosol determination using MAX-DOAS measurements will be divided in 4 tasks:

  • Software development for automatic application of the existing and extended aerosol algorithm. In particular automatic data quality assessment will be included. At the same time the aerosol retrieval algorithm will be optimised.

  • Validation of software and the optimised algorithm against data (Lidar, sun photometer, and in-situ measurements) from the network. Comparison of aerosol MAX-DOAS (AMD) with sun photometers poses no problem, as both types of instrument require sun-light for operation. Also, comparison of the AMD data with in-situ instrumentation (nephelometers, OPD’s, etc.), which operate independent of daylight, is no problem. However, the Raman LIDARs (RL), which derives range resolved aerosol extinction data, can only operate during periods of darkness. Thus comparison between RL and AMD can take place only in two ways: (i) During twilight hours, when both instruments can work. (ii) Interpolated data are actually compared, they can be augumented by sun photometer and Backscatter LIDAR (BL) data. In addition, comparison of AMD with BL data will be performed. Although BL only provides the backscatter ratio it can be operated during daylight hours. MAX-DOAS and aerosol optical instruments will be intercompared a t the following 3 sites: Melpitz (urban/background), Ispra (Continental southern Europe), Cabauw (Coastal/rural site).

  • Further develop the hardware of the MAX-DOAS instrument. In particular an existing prototype of the Mini-MAX-DOAS instrument is to be modified and extended in order to meet the following goals:
    - Stabilization of the function of an existing prototype for use in the open environment over longer periods (e.g. one year) without maintenance.
    - Hardening of the instrument casing according to the IP 64 concept, wide temperature range.
    - Automatic scanning in two orthogonal angle coordinates.
    - Optimization of the hard- and software interface between Laptop (or other small PC) and the MAX-DOAS instrument.
    This task will be performed by HMT (SME Hoffmann Messtechnik GmbH ).

  • Integration into the network. This task encompasses a test period to monitor the operation of the novel hardware (MAX-DOAS) within the existing network, and will also produce a demonstration data set.