Facility Description

Sampling Tower

The collection of aerosols and gases representative of the MBL must be conducted at an elevation above the local terrain in order to avoid contamination from sea spray, and from soil dust and other emissions from the land surface and other local sources. For this purpose, the original 23-m high walk-up tower was erected at Tudor Hill (32°15.87’N, 64°52.74’W) for the AEROCE project. The tower is located approximately 40 meters from the shoreline and at an altitude of approximately 30 meters above sea level. Two outboard platforms are attached at the top of the tower and provide 11.5 m2 of working area, where the meteorological sensors and various sampling systems are located. Space is available on the top platform for short or long term installations of user-specific equipment and equipment can also be mounted inboard or outboard at any point on the tower structure.

Improvements to operational safety were made during 2016, whereby a fall arrest system has been installed on the tower and all users are now required to undergo instruction on the use of a full body harness and to use this equipment when ascending and descending the tower.

Laboratory and Habitation Containers

Two converted 20-ft cargo containers serve as the electronics/instrument and chemistry/sample processing laboratories at the tower site. The electronics laboratory container houses the electrical distribution system for the facility, the sample controller system and data logging computers, communications (telephone with 4Mb DSL internet connection), refrigerator/freezer, various tools and spare parts and bench/floor space for housing users’ equipment. The chemistry laboratory container houses a water purification system, two laminar flow clean-air benches for processing aerosol and rainwater samples, and various reagents, containers and supplies used for sample processing and storage. Regular maintenance in the laboratory containers includes replacement of fluorescent light tubes and ballasts, replacement of cartridges for the water purification system, and replacement of HEPA- and pre- filters for the clean-air benches.

A third converted container was added in 2015 during the repair work conducted under award OCE-1536501 following damage sustained during hurricane Gonzalo. This is a custom-built habitation unit, with kitchen and dining area, and sleeping accommodation for two people. This was donated by the Atlantis Project (University of Laval, Canada) and makes a significant improvement to the facility by providing living facilities for scientists undertaking intensive on-site operations.

Data Logging and Sample Controller

Data logging and aerosol sampling is achieved using a Campbell Scientific CR1000 data logger and software. This enables sectored-controlled sampling, whereby the high-volume sampling pumps are activated when the wind is in a sector of 210-315° (i.e. the sector lying over the open ocean) and wind speeds are > 1 m.sec-1, and thus samples representative of the atmospheric boundary layer over the open ocean (i.e. the MBL) are collected with negligible local terrestrial influence. If local sources of contamination are not of concern, individual sample lines can be operated on a continuous basis, regardless of wind direction. The data control system can also be used to control any other additional equipment in this manner (i.e. sectored or non-sectored), as required. Remote access of the system from BIOS is achieved using the internet connection, allowing for timely system monitoring and troubleshooting.

Meterological Data

Meteorological data are acquired via an RM Young Marine Wind Monitor, model 05106 (WD and WS), a Vaisala temperature and relative humidity probe, model 41382 (T and RH), and an RM Young tipping bucket rain gauge, model 52203 (rainfall rate). These are mounted on top of the tower, downwind (relative to prevailing wind) from the aerosol and rain samplers. Atmospheric pressure at ground level at the base of the tower is measured using a Vaisala barometer, model PTB110. In addition to the tipping bucket rain gauge, rainfall is also measured using a manual rain gauge on top of the tower and at two locations at ground level close to the base of the tower.

Aerosol Sampling System

Adjacent to the base of the tower are three small aluminum shelters, which house the high-volume aerosol sampling pumps, thus protecting the scientific instruments and site operators from the heat and noise of the sampling pumps. There is also space available in these shelters for additional pumps and instrumentation as needed.

High volume aerosol samples are acquired using three Fuji high-volume brushless vacuum pumps, with continuous measurement of flow rates to determine the air volume sampled. Flow rates through each of the three vacuum lines are measured using FastFlo 620S insertion mass flow meters (Sierra Instruments, Inc.) connected to the main data logger. The vacuum lines are coupled via aluminum tubing and rubber hose connectors to the filter heads on the top of the tower which house 0.04 m2 effective area filters (e.g. for deployment of 8”x12” Whatman 41 cellulose or acid-washed quartz filters). Filters are mounted in cassettes made of polycarbonate or polyethylene which are clamped on anodized aluminum filter heads. One of these is used to collect archived weekly bulk aerosol samples and two sampling lines are available for use by facility users for project-specific sampling. A fourth unconnected filter head is used for collecting field blank filter samples. Loading and unloading of filter cassettes takes place under a laminar- flow clean-air hood in the laboratory van using clean handling techniques.

Precipitation Sampling System

The original two automatic rain collectors on the tower were replaced in 2011 with N-CON Atmospheric Deposition Samplers. One of these is dedicated to the weekly bulk sample archive efforts and the other sampler is available for users’ applications.

Archiving of Data and Samples

Briefly, all meteorological data and aerosol sampling data are recorded and backed-up on multiple computer systems at BIOS and also archived with the Biological and Chemical Oceanography Data Management Office (BCO-DMO), from where they are publicly accessible. Weekly rainwater samples are handled using trace-metal clean protocols and stored frozen, and aerosol filters are stored double bagged in evacuated desiccators. These samples are not currently analyzed but are maintained as an archive and available for use by interested parties.

User Fees

Modest facility-user fees are charged for the collection of data and/or samples by BIOS that require technician time or resources beyond the core activities, or for the use of the facility by other researchers in person. In 2017 these fees were $55.71 per week for NSF-funded projects, and $258.92 per week for other projects. These fees include institutional overhead, but do not cover sample shipping costs or the costs of specialized materials or other resources associated with the sampling or data collection, all of which are the obligation of the user. As with the current award, these facility-user fees will be credited to a facility time-share account, to be used for expenses directly related to the operation of the facility. Although the number of external science users of the facility over the proposed project period is not known a-priori, maximum net revenues of approximately $10,000 per year are predicted at full user capacity. This is well below the level of funding required to support the continued operation of the facility, hence the request to NSF for direct financial support of the facility.

Any net revenue from facility-user fees will be used to support the following items that are not included in the proposed budget: (1) salary for facility technician time required in excess of 3 months per year; (2) annual preventative and routine maintenance of the tower structure (estimated at approximately $5,000 per year); and (3) maintenance of facility grounds and structures (approximately $2,000 per year). In this way, external facility users will support components of the operation that are expected to increase in proportion to the number of tower users.