## 1 Introduction  
The air quality of highly urbanized cities is a major environmental and health concern as large amounts of air pollutants are produced rapidly by various anthropogenic activities. Along with carbon dioxide, short-lived climate pollutants (SLCP) including black carbon, methane, tropospheric ozone, and sulfate are responsible for up to 45% of the current global warming [1]. In addition, particulate matter (PM) pollution, especially when the size of the particle is smaller than 2.5 um in diameter, is especially dangerous to human health as it can be inhaled into the deepest portions of the lungs. The main components of PM pollution are usually black carbon and sulfate. Non-volatile particulate matter such as sulfate, crustal material, and black carbon are already easily measured by a variety of techniques [2; 3]. However, semi-volatile particulate matter such as ammonium nitrate, some organic materials, and water is more difficult to monitor. This is mainly because semi-volatile matter can escape from the particle samples during and after sampling for chemical analysis [4; 5]. The scattering of light incident on the particles depends on the physical properties of these particles, such as their average size and composition [6; 7]. Particles whose sizes are much smaller than the wavelength of the incident light are described through Rayleigh scattering whereas MIe scattering is more appropriate for particles whose diameter is similar to or larger than the wavelength of the incident light [8; 9]. By evaluating the MIe scattering of light by the particles through the collection of scattered light from multiple angles, the physical properties of the particles can be deduced. The collection of scattered light can be accomplished by using a single detector that sweeps through an arc about the illuminated particles, a technique called differential light scattering [10]. Alternatively, instead of using a single detector, multiple detectors can be placed equidistantly around the scattering particles such that the scattered light can be collected simultaneously at multiple angles. This technique called multiangle light scattering is faster than differential light scattering and is, therefore, one of the most widely used techniques for collecting the scattered light [11; 12]. In both techniques, the physical properties of the scattering particles are deduced from the angular dependence of the average intensity of the scattered light. However, the dependence of the scattering cross section on the wavelength of the incident light, the complex refractive index of the scatterer, the absorption coefficient of the scatter, and size of the scatter has not been investigated yet, especially in the context of lidar monitoring of particulate matter in the atmosphere. In this work, we perform numerical simulations to determine the angular dependence of the MIe scattering cross-section of pure water droplets, contaminated water droplets and black carbon as a function of the wavelength of the incident laser light, complex refractive index of the scatterer, and size of the scatterer. Most atmospheric particles are not spherical. Thus, the prediction of their scattering properties using Mie theory is a crude approximation [13]. To account for the complexity of atmospheric particles, other groups have used more sophisticated light scattering models such as the T-Matrix method for aggregates and colloid particles [14; 15; 16; 17], the Discrete Dipole Approximation for irregularly shaped particles [18; 19] or Hybrid approaches for facet particles [20; 21]. Dynamic light scattering (DLS) can also analyze the size of particles and determine the size distribution profile of small particles in suspension, even though multiple measurements are needed to obtain a smooth correlation function and a reasonable average particle size [22]. DLS utilizes a continuous wave laser source to perform measurements with a duration of several tens of seconds, making it inappropriate for time-gated measurement techniques.