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Techniques for Estimating Generation and Non-ventilation Removal Rates of Volatile Organic Compound using the Near-field/far-field (NF/FF) model

Abstract No:

1682

Abstract Type:

Student Poster

Authors:

C Chen¹, P Tsai¹

Institutions:

¹National Cheng Kung University, Tainan, TWN

Presenter:

Chun-Yu Chen
National Cheng Kung University

Faculty Advisor:

Perng-Jy Tsai
National Cheng Kung University

Description:

In many real-world scenarios, direct measurement data are often limited by high costs. To address these challenges, mathematical exposure models serve as critical supplementary tools. the near-field/far-field (NF/FF) model was developed to partition indoor spaces into two zones: a near-field (NF) representing the immediate vicinity of the source and the worker's breathing zone, and a far-field (FF) representing the rest of the room. NF/FF models are widely used to estimate indoor exposure concentrations; however, their application has largely been restricted to known generation rates and neglected non-ventilation removal, limiting relevance to realistic workplaces.

Situation/Problem:

A significant limitation in the current application of the NF/FF model is the reliance on predefined or assumed pollutant generation rates (G) and the frequent neglect of non-ventilation removal rates (K). This study addresses these gaps by developing a technique to estimate both G and K from time-resolved concentration data.

Methods:

Controlled chamber experiments were conducted in a simulated classroom and the isopropyl alcohol (IPA) was selected as the target VOC. The consumption rates of IPA were regulated by a peristaltic pump, and the Photoionization detectors (PIDs) were placed in the near-field and far-field to measure concentrations under three air change rates (ACH = 1, 2, and 3).
The NF/FF model is founded on the principle of mass conservation. The indoor environment is conceptualized as two interconnected, well-mixed zones with a constant interzonal air exchange rate, denoted as β. To solve the NF/FF model equations for practical application, this study utilizes a numerical iteration method based on the first-order Runge–Kutta scheme to simulate concentration changes over discrete time intervals. This numerical approach allows for the dynamic fitting of the model to experimental data. G and K could be estimated by fitting discretized equations to measured concentrations using least-squares optimization.

Results / Conclusions:

The NF/FF model demonstrated exceptional accuracy in reconstructing the pollutant generation rate for single-source scenarios. Across the three ventilation conditions, the relative errors between the model and actual G ranged from -1.6% to -0.3%. These results confirm that the inverse estimation technique is highly stable and reproducible. The model successfully identified the source strength without requiring it to be predefined. The non-ventilation removal rates (K) were found to be negligible across all conditions. This finding validates the assumption that for highly volatile and low-adsorptive compounds like IPA, concentration decay is dominated by ventilation. Model performance was stable across ventilation rates, with near-field and far-field RMSE ~4–5 and ~2–3 ppm, respectively.

Core Competencies:

Exposure Assessment

Secondary Core Competencies:

Chemical Hazards

Keywords

Choose at least one (1), and up to five, (5) keywords from the following list. These selections will optimize your presentation's search results for attendees.

Exposure Assessment

Indoor air quality

Real-time detection services and direct reading instruments

Risk assessment and management

Targeted Audience (IH/OH Practice Level)

Based on the information that will be presented during your proposed session, please indicate the targeted audience practice level: (select one)

Professional: Professional is a job title given to persons who have obtained a baccalaureate or graduate degree in IH/OH, public health, safety, environmental sciences, biology, chemistry, physics, or engineering or who have a degree in another area that meets the standards set forth in the next section, Knowledge and Skill Sets of IH/OH Practice Levels, and has had 4 or more years of practice. One significant way of demonstrating professional competence is to achieve certification by a 3rd party whose certification scheme is recognized by the International Occupational Hygiene Association (IOHA) such as the Board of Global EHS Credentialing (BGC).

Volunteer Groups

Was this session organized by an AIHA Technical Committee, Special Interest Group, Working Group, Advisory Group or other AIHA project Team?

Worker Exposure Data and/ or Results

Are worker exposure data and/or results of worker exposure data analysis presented?

Practical Application

How will this help advance the science of IH/OH?

This study successfully established a modeling technique to estimate unknown generation and removal parameters using the NF/FF model. The inverse estimation method using least-squares optimization is a reliable way to accurately determine pollutant emission rates and non-ventilation removal rate. The model successfully identified the source strength and non-ventilation removal rate without requiring it to be predefined, which is a major advancement for assessing exposure in workplaces with the use of mathematical exposure models.