Indoor air quality in new and renovated low‐income apartments with mechanical ventilation and natural gas cooking in California

This study presents pollutant concentrations and performance data for code-required mechanical ventilation equipment in 23 low-income apartments at 4 properties constructed or renovated 2013-2017. All apartments had natural gas cooking burners. Occupants pledged to not use windows for ventilation during the study but several did. Measured airflows of range hoods and bathroom exhaust fans were lower than product specifications. Only eight apartments operationally met all ventilation code requirements. Pollutants measured over one week in each apartment included time-resolved fine particulate matter (PM2.5), nitrogen dioxide (NO2), formaldehyde and carbon dioxide (CO2) and time-integrated formaldehyde, NO2 and nitrogen oxides (NOX). Compared to a recent study of California houses with code-compliant ventilation, apartments were smaller, had fewer occupants, higher densities, and higher mechanical ventilation rates. Mean PM2.5, formaldehyde, NO2, and CO2 were 7.7 µg/m3, 14.1 ppb, 18.8 ppb, and 741 ppm in apartments; these are 4% lower, 25% lower, 165% higher, and 18% higher compared to houses with similar cooking frequency. Four apartments had weekly PM2.5 above the California annual outdoor standard of 12 µg/m3 and also discrete days above the World Health Organization 24-h guideline of 25 µg/m3. Two apartments had weekly NO2 above the California annual outdoor standard of 30 ppb.

Methods
This study evaluated IAQ in 23 low-income apartments at 4 properties with natural gas cooking burners and mechanical ventilation equipment having specifications that met state building code requirements. The inclusion criteria were for apartment units to have (1) mechanical ventilation (MV) equipment that met the requirements of California’s Title 24 residential building code and (2) a natural gas cooking appliance. Required MV equipment were an exhaust fan in each bathroom, a kitchen exhaust fan or range hood, and equipment providing regular ventilation to the dwelling unit – each having specifications that met the code-minimum airflow requirements.

Each property was visited in advance of the week of monitoring to confirm the presence of compliant MV equipment; this was done by inspecting 2-4 unoccupied units per site. Recruitment commenced following this visit. During the first visit, teams provided the participant with a paper version of the survey to obtain information about satisfaction with air quality and thermal conditions in the home and routine activities that impact ventilation and IAQ. Characteristics of mechanical ventilation equipment, cooking appliances, and thermal conditioning systems were documented and unit airtightness and ventilation equipment airflows were measured. Temperature, humidity, carbon dioxide and air pollutant concentrations were measured inside each apartment and air pollutant concentrations were measured outdoors on site. Sensors were installed to monitor use of gas cooking burners, ventilation equipment, and natural ventilation. Participants were asked to record occupancy and activities during each day of monitoring. Surveys and activity logs were collected and equipment was removed after one week of monitoring in each apartment.

The study was led by Lawrence Berkeley National Laboratory (LBNL). Association for Energy Affordability recruited study buildings and completed a large portion of the field work. All study protocols involving interactions and collection of data from private individuals and monitoring in occupied homes were reviewed and approved by the LBNL Human Subjects Committee. Research Funding and technical contributions of collaborators are noted below in the acknowledgements.