Access Sensor Technologies has sold three different versions of our Ultrasonic Personal Air Sampler (UPAS) since 2017: the UPAS v2.0, UPAS v2.1, and UPAS v2.1 PLUS. Not sure which of these you have? The visual indicators that you can use to distinguish between these three models are noted in Figure 1. Keep reading to learn more about: (1) the differences between these three UPAS models as well as (2) where you can find the user guide and other documentation for each.

Figure 1. Key features that can be used to distinguish the UPAS v2.0 from the UPAS v2.1 and the UPAS v2.1 PLUS are indicated with red arrows and text.

UPAS v2.0

The UPAS v2.0 is a wearable particulate matter (PM) sampler that logs time-resolved data on temperature, relative humidity, atmospheric pressure, the sample flow rate, and the GPS location of the device. We sold the UPAS v2.0 from 2017 to 2022.

• There is no light sensor on the front and
• The serial ID on the back of the housing starts with "PS" followed by four numbers (see Figure 1). 

We no longer sell the UPAS v2.0, but we do still support and service these devices. You can find documentation for the UPAS v2.0 on the product webpage. Note that the user guide for the UPAS v2.0 differs from the user guide for the UPAS v2.1 and v2.1 PLUS. The UPAS v2.0 also requires different iOS and Android mobile applications than the UPAS v2.1 or v2.1 PLUS. Search for "CSU UPAS" in the Apple App store.

UPAS v2.1

We started selling the UPAS v2.1 in 2022. The UPAS v2.1 is the successor to the UPAS v2.0. The UPAS v2.1 includes two new features that were not included in the v2.0: (1) a light sensor and (2) an accelerometer.

• There is a light sensor on the front and
• The serial ID on the back housing starts with “PSP” followed by five numbers but
• There is no PM sensor housing on the front of the UPAS (see Figure 1).

We still sell the UPAS v2.1. You can find documentation for the UPAS v2.1 on the product webpage. Note that the user guide for the UPAS v2.1 differs from that for the UPAS v2.0. The UPAS v2.1 also requires different iOS and Android mobile applications than the UPAS v2.0. Search for "AST UPAS" in the Apple App Store or on Google Play.

Prior to May 2025, UPAS v2.1 were shipped with firmware version 157 installed; since May 2025, UPAS v2.1 have been shipped with firmware version ≥200 installed. We’ve released two different user guides for firmware versions ≤158 and ≥200. We recommend downloading the latest firmware from the UPAS v2.1 product webpage and following the instructions in the user guide to install the latest firmware on your UPAS v2.1.

UPAS v2.1 PLUS

We started selling the UPAS v2.1 PLUS in 2022. The UPAS v2.1 PLUS includes all of the same features as the UPAS v2.1, plus a time-resolved optical PM sensor (the Sensirion SPS30). The UPAS v2.1 PLUS can log time- and location-resolved data from the PM sensor while also collecting a filter sample of PM.

• There is a light sensor on the front,
• The serial ID on the back housing starts with “PSP” followed by five numbers, and
• There is a PM sensor housing on the front of the UPAS (see Figure 1).

We still sell the UPAS v2.1 PLUS. You can find documentation for the UPAS v2.1 PLUS on the product webpage. The user guide, mobile applications, and device firmware for the UPAS v2.1 PLUS are the same as for the UPAS v2.1.