Mercury Evaporation Rate Calculator

Mercury Evaporation Rate Calculator

Standard room temperature is usually 20°C – 25°C.

A single large drop of mercury (~1g) is roughly 0.5 – 1.0 cm².

Stagnant air: 0.05 m/s | HVAC airflow: 0.2 – 0.5 m/s.

Calculation Results

Rate (mg/hour) 0.00

Rate (μg/hour) 0.00

Vapor Pressure (Pa) 0.00

Daily Release (mg/day) 0.00

Note: This calculation provides an estimate based on mass transfer coefficients for elemental mercury at standard pressure. Actual concentrations depend on room volume and air exchange rates.

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Understanding Mercury Evaporation

Elemental mercury (Hg) is unique because it is a liquid at room temperature that readily transitions into a colorless, odorless vapor. While a mercury spill might look contained, the invisible evaporation process can lead to hazardous indoor air quality. This Mercury Evaporation Rate Calculator helps safety professionals and homeowners estimate the speed at which liquid mercury turns into gas.

The Physics of Mercury Vaporization

The rate at which mercury evaporates is determined by several physical variables. Unlike water, mercury has a high surface tension but a significant vapor pressure even at cool temperatures. The evaporation is primarily governed by the Antoine Equation for vapor pressure and mass transfer dynamics.

• Temperature: As temperature increases, the kinetic energy of mercury atoms rises, significantly increasing vapor pressure. A small increase in room temperature (from 20°C to 30°C) can nearly double the evaporation rate.
• Surface Area: Mercury often breaks into tiny "beads" when spilled. Because evaporation only occurs at the surface, many small beads create a much larger total surface area than one large pool, leading to faster vaporization.
• Airflow: Moving air carries mercury molecules away from the surface of the liquid, maintaining a steep concentration gradient and accelerating the process.

Calculating the Rate: The Math

The calculator uses an empirical mass transfer model. First, it determines the Vapor Pressure ($P$) of mercury in Pascals using the following formula:

log10(P_Pa) = 10.572 – (3236 / T_Kelvin)

The evaporation rate is then estimated considering the mass transfer coefficient ($K$), which is sensitive to air velocity ($v$). For typical indoor scenarios, the rate $E$ (mg/hr) is proportional to the surface area and the vapor pressure gradient.

Safety Guidelines for Mercury Spills

If you have used this calculator because of a spill, remember these critical safety steps:

1. Evacuate: Keep children and pets away from the area.
2. Isolate: Turn off central heating or air conditioning to prevent the spread of vapors through the building.
3. Ventilate: Open windows to the outside to dilute vapor concentrations.
4. No Vacuums: Never use a vacuum cleaner or broom, as this breaks mercury into smaller beads and increases the surface area, drastically increasing the evaporation rate.

Example Calculation

Imagine a broken thermometer results in 0.5 cm² of exposed mercury in a room at 22°C (295.15 K) with a slight breeze (0.2 m/s).

1. Vapor Pressure: At 22°C, the vapor pressure is approximately 0.19 Pascals.
2. Calculation: The resulting evaporation rate would be approximately 0.004 mg/hr.

While this number seems small, the EPA action level for mercury vapor is very low (0.001 mg/m³), meaning even slow evaporation can quickly contaminate the air in a confined space.

function calculateMercuryEvap() { // Get inputs var tempC = parseFloat(document.getElementById("tempCelsius").value); var area = parseFloat(document.getElementById("surfaceArea").value); var velocity = parseFloat(document.getElementById("airVelocity").value); // Validation if (isNaN(tempC) || isNaN(area) || isNaN(velocity) || area <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Constants var tempK = tempC + 273.15; // 1. Calculate Vapor Pressure of Mercury in Pascals // Formula: log10(P_Pa) = 10.572 – 3236 / T var logP = 10.572 – (3236 / tempK); var vPressPa = Math.pow(10, logP); // 2. Mass Transfer Coefficient (Empirical approximation for Hg) // K is often modeled as proportional to velocity^0.78 // We'll use a standard environmental engineering approximation: // Rate (mg/h) = (K * Area * P * M) / (R * T) // Simplified for mercury: Rate (mg/h) = Area(cm2) * P(Pa) * (0.015 * v^0.78) var vFactor = Math.pow(velocity + 0.05, 0.78); // 0.05 is base diffusion in still air var rateMgHr = area * vPressPa * (0.045 * vFactor); // Adjustments for temperature dependency of diffusion rateMgHr = rateMgHr * (tempK / 298.15); // Calculations for display var rateUgHr = rateMgHr * 1000; var rateMgDay = rateMgHr * 24; // Display results document.getElementById("mercury-result").style.display = "block"; document.getElementById("rateMgHr").innerText = rateMgHr.toFixed(4); document.getElementById("rateUgHr").innerText = rateUgHr.toFixed(2); document.getElementById("vaporPressure").innerText = vPressPa.toFixed(4); document.getElementById("rateMgDay").innerText = rateMgDay.toFixed(3); // Scroll to results document.getElementById("mercury-result").scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }